[PATCH 01/16] fs: add an iopoll method to struct file_operations

[PATCH 01/16] fs: add an iopoll method to struct file_operations

[Jens Axboe]

From: Christoph Hellwig <hch@lst.de>

This new methods is used to explicitly poll for I/O completion for an
iocb.  It must be called for any iocb submitted asynchronously (that
is with a non-null ki_complete) which has the IOCB_HIPRI flag set.

The method is assisted by a new ki_cookie field in struct iocb to store
the polling cookie.

TODO: we can probably union ki_cookie with the existing hint and I/O
priority fields to avoid struct kiocb growth.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 Documentation/filesystems/vfs.txt | 3 +++
 include/linux/fs.h                | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 8dc8e9c2913f..761c6fd24a53 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -857,6 +857,7 @@ struct file_operations {
 	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
 	ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
 	ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
+	int (*iopoll)(struct kiocb *kiocb, bool spin);
 	int (*iterate) (struct file *, struct dir_context *);
 	int (*iterate_shared) (struct file *, struct dir_context *);
 	__poll_t (*poll) (struct file *, struct poll_table_struct *);
@@ -902,6 +903,8 @@ otherwise noted.
 
   write_iter: possibly asynchronous write with iov_iter as source
 
+  iopoll: called when aio wants to poll for completions on HIPRI iocbs
+
   iterate: called when the VFS needs to read the directory contents
 
   iterate_shared: called when the VFS needs to read the directory contents
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 811c77743dad..ccb0b7a63aa5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -310,6 +310,7 @@ struct kiocb {
 	int			ki_flags;
 	u16			ki_hint;
 	u16			ki_ioprio; /* See linux/ioprio.h */
+	unsigned int		ki_cookie; /* for ->iopoll */
 } __randomize_layout;
 
 static inline bool is_sync_kiocb(struct kiocb *kiocb)
@@ -1786,6 +1787,7 @@ struct file_operations {
 	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
 	ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
 	ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
+	int (*iopoll)(struct kiocb *kiocb, bool spin);
 	int (*iterate) (struct file *, struct dir_context *);
 	int (*iterate_shared) (struct file *, struct dir_context *);
 	__poll_t (*poll) (struct file *, struct poll_table_struct *);
-- 
2.17.1

[PATCH 02/16] block: wire up block device iopoll method

[Jens Axboe]

From: Christoph Hellwig <hch@lst.de>

Just call blk_poll on the iocb cookie, we can derive the block device
from the inode trivially.

Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/block_dev.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index c546cdce77e6..5415579f3e14 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -279,6 +279,14 @@ struct blkdev_dio {
 
 static struct bio_set blkdev_dio_pool;
 
+static int blkdev_iopoll(struct kiocb *kiocb, bool wait)
+{
+	struct block_device *bdev = I_BDEV(kiocb->ki_filp->f_mapping->host);
+	struct request_queue *q = bdev_get_queue(bdev);
+
+	return blk_poll(q, READ_ONCE(kiocb->ki_cookie), wait);
+}
+
 static void blkdev_bio_end_io(struct bio *bio)
 {
 	struct blkdev_dio *dio = bio->bi_private;
@@ -396,6 +404,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
 				bio->bi_opf |= REQ_HIPRI;
 
 			qc = submit_bio(bio);
+			WRITE_ONCE(iocb->ki_cookie, qc);
 			break;
 		}
 
@@ -2068,6 +2077,7 @@ const struct file_operations def_blk_fops = {
 	.llseek		= block_llseek,
 	.read_iter	= blkdev_read_iter,
 	.write_iter	= blkdev_write_iter,
+	.iopoll		= blkdev_iopoll,
 	.mmap		= generic_file_mmap,
 	.fsync		= blkdev_fsync,
 	.unlocked_ioctl	= block_ioctl,
-- 
2.17.1

[PATCH 03/16] block: add bio_set_polled() helper

[Jens Axboe]

For the upcoming async polled IO, we can't sleep allocating requests.
If we do, then we introduce a deadlock where the submitter already
has async polled IO in-flight, but can't wait for them to complete
since polled requests must be active found and reaped.

Utilize the helper in the blockdev DIRECT_IO code.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/block_dev.c      |  4 ++--
 include/linux/bio.h | 14 ++++++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 5415579f3e14..2ebd2a0d7789 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -233,7 +233,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
 		task_io_account_write(ret);
 	}
 	if (iocb->ki_flags & IOCB_HIPRI)
-		bio.bi_opf |= REQ_HIPRI;
+		bio_set_polled(&bio, iocb);
 
 	qc = submit_bio(&bio);
 	for (;;) {
@@ -401,7 +401,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
 		nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES);
 		if (!nr_pages) {
 			if (iocb->ki_flags & IOCB_HIPRI)
-				bio->bi_opf |= REQ_HIPRI;
+				bio_set_polled(bio, iocb);
 
 			qc = submit_bio(bio);
 			WRITE_ONCE(iocb->ki_cookie, qc);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 7380b094dcca..f6f0a2b3cbc8 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -823,5 +823,19 @@ static inline int bio_integrity_add_page(struct bio *bio, struct page *page,
 
 #endif /* CONFIG_BLK_DEV_INTEGRITY */
 
+/*
+ * Mark a bio as polled. Note that for async polled IO, the caller must
+ * expect -EWOULDBLOCK if we cannot allocate a request (or other resources).
+ * We cannot block waiting for requests on polled IO, as those completions
+ * must be found by the caller. This is different than IRQ driven IO, where
+ * it's safe to wait for IO to complete.
+ */
+static inline void bio_set_polled(struct bio *bio, struct kiocb *kiocb)
+{
+	bio->bi_opf |= REQ_HIPRI;
+	if (!is_sync_kiocb(kiocb))
+		bio->bi_opf |= REQ_NOWAIT;
+}
+
 #endif /* CONFIG_BLOCK */
 #endif /* __LINUX_BIO_H */
-- 
2.17.1

[PATCH 04/16] iomap: wire up the iopoll method

[Jens Axboe]

From: Christoph Hellwig <hch@lst.de>

Store the request queue the last bio was submitted to in the iocb
private data in addition to the cookie so that we find the right block
device.  Also refactor the common direct I/O bio submission code into a
nice little helper.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Modified to use bio_set_polled().

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/gfs2/file.c        |  2 ++
 fs/iomap.c            | 43 ++++++++++++++++++++++++++++---------------
 fs/xfs/xfs_file.c     |  1 +
 include/linux/iomap.h |  1 +
 4 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index a2dea5bc0427..58a768e59712 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -1280,6 +1280,7 @@ const struct file_operations gfs2_file_fops = {
 	.llseek		= gfs2_llseek,
 	.read_iter	= gfs2_file_read_iter,
 	.write_iter	= gfs2_file_write_iter,
+	.iopoll		= iomap_dio_iopoll,
 	.unlocked_ioctl	= gfs2_ioctl,
 	.mmap		= gfs2_mmap,
 	.open		= gfs2_open,
@@ -1310,6 +1311,7 @@ const struct file_operations gfs2_file_fops_nolock = {
 	.llseek		= gfs2_llseek,
 	.read_iter	= gfs2_file_read_iter,
 	.write_iter	= gfs2_file_write_iter,
+	.iopoll		= iomap_dio_iopoll,
 	.unlocked_ioctl	= gfs2_ioctl,
 	.mmap		= gfs2_mmap,
 	.open		= gfs2_open,
diff --git a/fs/iomap.c b/fs/iomap.c
index a3088fae567b..4ee50b76b4a1 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -1454,6 +1454,28 @@ struct iomap_dio {
 	};
 };
 
+int iomap_dio_iopoll(struct kiocb *kiocb, bool spin)
+{
+	struct request_queue *q = READ_ONCE(kiocb->private);
+
+	if (!q)
+		return 0;
+	return blk_poll(q, READ_ONCE(kiocb->ki_cookie), spin);
+}
+EXPORT_SYMBOL_GPL(iomap_dio_iopoll);
+
+static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
+		struct bio *bio)
+{
+	atomic_inc(&dio->ref);
+
+	if (dio->iocb->ki_flags & IOCB_HIPRI)
+		bio_set_polled(bio, dio->iocb);
+
+	dio->submit.last_queue = bdev_get_queue(iomap->bdev);
+	dio->submit.cookie = submit_bio(bio);
+}
+
 static ssize_t iomap_dio_complete(struct iomap_dio *dio)
 {
 	struct kiocb *iocb = dio->iocb;
@@ -1566,7 +1588,7 @@ static void iomap_dio_bio_end_io(struct bio *bio)
 	}
 }
 
-static blk_qc_t
+static void
 iomap_dio_zero(struct iomap_dio *dio, struct iomap *iomap, loff_t pos,
 		unsigned len)
 {
@@ -1580,15 +1602,10 @@ iomap_dio_zero(struct iomap_dio *dio, struct iomap *iomap, loff_t pos,
 	bio->bi_private = dio;
 	bio->bi_end_io = iomap_dio_bio_end_io;
 
-	if (dio->iocb->ki_flags & IOCB_HIPRI)
-		flags |= REQ_HIPRI;
-
 	get_page(page);
 	__bio_add_page(bio, page, len, 0);
 	bio_set_op_attrs(bio, REQ_OP_WRITE, flags);
-
-	atomic_inc(&dio->ref);
-	return submit_bio(bio);
+	iomap_dio_submit_bio(dio, iomap, bio);
 }
 
 static loff_t
@@ -1691,9 +1708,6 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
 				bio_set_pages_dirty(bio);
 		}
 
-		if (dio->iocb->ki_flags & IOCB_HIPRI)
-			bio->bi_opf |= REQ_HIPRI;
-
 		iov_iter_advance(dio->submit.iter, n);
 
 		dio->size += n;
@@ -1701,11 +1715,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
 		copied += n;
 
 		nr_pages = iov_iter_npages(&iter, BIO_MAX_PAGES);
-
-		atomic_inc(&dio->ref);
-
-		dio->submit.last_queue = bdev_get_queue(iomap->bdev);
-		dio->submit.cookie = submit_bio(bio);
+		iomap_dio_submit_bio(dio, iomap, bio);
 	} while (nr_pages);
 
 	/*
@@ -1916,6 +1926,9 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 	if (dio->flags & IOMAP_DIO_WRITE_FUA)
 		dio->flags &= ~IOMAP_DIO_NEED_SYNC;
 
+	WRITE_ONCE(iocb->ki_cookie, dio->submit.cookie);
+	WRITE_ONCE(iocb->private, dio->submit.last_queue);
+
 	if (!atomic_dec_and_test(&dio->ref)) {
 		if (!dio->wait_for_completion)
 			return -EIOCBQUEUED;
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index e47425071e65..60c2da41f0fc 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1203,6 +1203,7 @@ const struct file_operations xfs_file_operations = {
 	.write_iter	= xfs_file_write_iter,
 	.splice_read	= generic_file_splice_read,
 	.splice_write	= iter_file_splice_write,
+	.iopoll		= iomap_dio_iopoll,
 	.unlocked_ioctl	= xfs_file_ioctl,
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= xfs_file_compat_ioctl,
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 9a4258154b25..0fefb5455bda 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -162,6 +162,7 @@ typedef int (iomap_dio_end_io_t)(struct kiocb *iocb, ssize_t ret,
 		unsigned flags);
 ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 		const struct iomap_ops *ops, iomap_dio_end_io_t end_io);
+int iomap_dio_iopoll(struct kiocb *kiocb, bool spin);
 
 #ifdef CONFIG_SWAP
 struct file;
-- 
2.17.1

[PATCH 05/16] Add io_uring IO interface

[Jens Axboe]

The submission queue (SQ) and completion queue (CQ) rings are shared
between the application and the kernel. This eliminates the need to
copy data back and forth to submit and complete IO.

IO submissions use the io_uring_sqe data structure, and completions
are generated in the form of io_uring_sqe data structures. The SQ
ring is an index into the io_uring_sqe array, which makes it possible
to submit a batch of IOs without them being contiguous in the ring.
The CQ ring is always contiguous, as completion events are inherently
unordered and can point to any io_uring_iocb.

Two new system calls are added for this:

io_uring_setup(entries, iovecs, params)
	Sets up a context for doing async IO. On success, returns a file
	descriptor that the application can mmap to gain access to the
	SQ ring, CQ ring, and io_uring_iocbs.

io_uring_enter(fd, to_submit, min_complete, flags)
	Initiates IO against the rings mapped to this fd, or waits for
	them to complete, or both The behavior is controlled by the
	parameters passed in. If 'min_complete' is non-zero, then we'll
	try and submit new IO. If IORING_ENTER_GETEVENTS is set, the
	kernel will wait for 'min_complete' events, if they aren't
	already available.

With this setup, it's possible to do async IO with a single system
call. Future developments will enable polled IO with this interface,
and polled submission as well. The latter will enable an application
to do IO without doing ANY system calls at all.

For IRQ driven IO, an application only needs to enter the kernel for
completions if it wants to wait for them to occur.

Each io_uring is backed by a workqueue, to support buffered async IO
as well. We will only punt to an async context if the command would
need to wait for IO on the device side. Any data that can be accessed
directly in the page cache is done inline. This avoids the slowness
issue of usual threadpools, since cached data is accessed as quickly
as a sync interface.

Sample application: http://git.kernel.dk/cgit/fio/plain/t/io_uring.c

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 arch/x86/entry/syscalls/syscall_32.tbl |   2 +
 arch/x86/entry/syscalls/syscall_64.tbl |   2 +
 fs/Makefile                            |   1 +
 fs/io_uring.c                          | 977 +++++++++++++++++++++++++
 include/linux/syscalls.h               |   5 +
 include/uapi/linux/io_uring.h          |  97 +++
 init/Kconfig                           |   9 +
 kernel/sys_ni.c                        |   2 +
 8 files changed, 1095 insertions(+)
 create mode 100644 fs/io_uring.c
 create mode 100644 include/uapi/linux/io_uring.h

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 3cf7b533b3d1..194e79c0032e 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -398,3 +398,5 @@
 384	i386	arch_prctl		sys_arch_prctl			__ia32_compat_sys_arch_prctl
 385	i386	io_pgetevents		sys_io_pgetevents		__ia32_compat_sys_io_pgetevents
 386	i386	rseq			sys_rseq			__ia32_sys_rseq
+387	i386	io_uring_setup		sys_io_uring_setup		__ia32_compat_sys_io_uring_setup
+388	i386	io_uring_enter		sys_io_uring_enter		__ia32_sys_io_uring_enter
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index f0b1709a5ffb..453ff7a79002 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -343,6 +343,8 @@
 332	common	statx			__x64_sys_statx
 333	common	io_pgetevents		__x64_sys_io_pgetevents
 334	common	rseq			__x64_sys_rseq
+335	common	io_uring_setup		__x64_sys_io_uring_setup
+336	common	io_uring_enter		__x64_sys_io_uring_enter
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/fs/Makefile b/fs/Makefile
index 293733f61594..8e15d6fc4340 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -30,6 +30,7 @@ obj-$(CONFIG_TIMERFD)		+= timerfd.o
 obj-$(CONFIG_EVENTFD)		+= eventfd.o
 obj-$(CONFIG_USERFAULTFD)	+= userfaultfd.o
 obj-$(CONFIG_AIO)               += aio.o
+obj-$(CONFIG_IO_URING)		+= io_uring.o
 obj-$(CONFIG_FS_DAX)		+= dax.o
 obj-$(CONFIG_FS_ENCRYPTION)	+= crypto/
 obj-$(CONFIG_FILE_LOCKING)      += locks.o
diff --git a/fs/io_uring.c b/fs/io_uring.c
new file mode 100644
index 000000000000..148eb3af7dc4
--- /dev/null
+++ b/fs/io_uring.c
@@ -0,0 +1,977 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Shared application/kernel submission and completion ring pairs, for
+ * supporting fast/efficient IO.
+ *
+ * Copyright (C) 2019 Jens Axboe
+ */
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/errno.h>
+#include <linux/syscalls.h>
+#include <linux/compat.h>
+#include <linux/refcount.h>
+#include <linux/uio.h>
+
+#include <linux/sched/signal.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/fdtable.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/mmu_context.h>
+#include <linux/percpu.h>
+#include <linux/slab.h>
+#include <linux/workqueue.h>
+#include <linux/blkdev.h>
+#include <linux/anon_inodes.h>
+#include <linux/sched/mm.h>
+
+#include <linux/uaccess.h>
+#include <linux/nospec.h>
+
+#include <uapi/linux/io_uring.h>
+
+#include "internal.h"
+
+struct io_uring {
+	u32 head ____cacheline_aligned_in_smp;
+	u32 tail ____cacheline_aligned_in_smp;
+};
+
+struct io_sq_ring {
+	struct io_uring		r;
+	u32			ring_mask;
+	u32			ring_entries;
+	u32			dropped;
+	u32			flags;
+	u32			array[];
+};
+
+struct io_cq_ring {
+	struct io_uring		r;
+	u32			ring_mask;
+	u32			ring_entries;
+	u32			overflow;
+	struct io_uring_cqe	cqes[];
+};
+
+struct io_ring_ctx {
+	struct percpu_ref	refs;
+
+	unsigned int		flags;
+	bool			compat;
+
+	/* SQ ring */
+	struct io_sq_ring	*sq_ring;
+	unsigned		sq_entries;
+	unsigned		sq_mask;
+	unsigned		sq_thread_cpu;
+	struct io_uring_sqe	*sq_sqes;
+
+	/* CQ ring */
+	struct io_cq_ring	*cq_ring;
+	unsigned		cq_entries;
+	unsigned		cq_mask;
+
+	/* IO offload */
+	struct workqueue_struct	*sqo_wq;
+	struct mm_struct	*sqo_mm;
+	struct files_struct	*sqo_files;
+
+	struct completion	ctx_done;
+
+	struct {
+		struct mutex		uring_lock;
+		wait_queue_head_t	wait;
+	} ____cacheline_aligned_in_smp;
+
+	struct {
+		spinlock_t		completion_lock;
+	} ____cacheline_aligned_in_smp;
+};
+
+struct sqe_submit {
+	const struct io_uring_sqe *sqe;
+	unsigned index;
+};
+
+struct io_work {
+	struct work_struct work;
+	struct sqe_submit submit;
+};
+
+struct io_kiocb {
+	union {
+		struct kiocb		rw;
+		struct io_work		work;
+	};
+
+	struct io_ring_ctx	*ctx;
+	struct list_head	list;
+	unsigned long		flags;
+#define REQ_F_FORCE_NONBLOCK	1	/* inline submission attempt */
+	u64			user_data;
+};
+
+#define IO_PLUG_THRESHOLD		2
+
+static struct kmem_cache *req_cachep;
+
+static const struct file_operations io_uring_fops;
+
+static void io_ring_ctx_ref_free(struct percpu_ref *ref)
+{
+	struct io_ring_ctx *ctx = container_of(ref, struct io_ring_ctx, refs);
+
+	complete(&ctx->ctx_done);
+}
+
+static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
+{
+	struct io_ring_ctx *ctx;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return NULL;
+
+	if (percpu_ref_init(&ctx->refs, io_ring_ctx_ref_free, 0, GFP_KERNEL)) {
+		kfree(ctx);
+		return NULL;
+	}
+
+	ctx->flags = p->flags;
+	init_completion(&ctx->ctx_done);
+	spin_lock_init(&ctx->completion_lock);
+	init_waitqueue_head(&ctx->wait);
+	mutex_init(&ctx->uring_lock);
+	return ctx;
+}
+
+static void io_inc_cqring(struct io_ring_ctx *ctx)
+{
+	struct io_cq_ring *ring = ctx->cq_ring;
+
+	ring->r.tail++;
+	smp_wmb();
+}
+
+static struct io_uring_cqe *io_peek_cqring(struct io_ring_ctx *ctx)
+{
+	struct io_cq_ring *ring = ctx->cq_ring;
+	unsigned tail;
+
+	smp_rmb();
+	tail = READ_ONCE(ring->r.tail);
+	if (tail + 1 == READ_ONCE(ring->r.head))
+		return NULL;
+
+	return &ring->cqes[tail & ctx->cq_mask];
+}
+
+static void __io_cqring_fill_event(struct io_ring_ctx *ctx, u64 ki_user_data,
+				   long res, unsigned ev_flags)
+{
+	struct io_uring_cqe *cqe;
+
+	/*
+	 * If we can't get a cq entry, userspace overflowed the
+	 * submission (by quite a lot). Increment the overflow count in
+	 * the ring.
+	 */
+	cqe = io_peek_cqring(ctx);
+	if (cqe) {
+		cqe->user_data = ki_user_data;
+		cqe->res = res;
+		cqe->flags = ev_flags;
+		smp_wmb();
+		io_inc_cqring(ctx);
+	} else
+		ctx->cq_ring->overflow++;
+}
+
+static void io_cqring_fill_event(struct io_ring_ctx *ctx, u64 ki_user_data,
+				 long res, unsigned ev_flags)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&ctx->completion_lock, flags);
+	__io_cqring_fill_event(ctx, ki_user_data, res, ev_flags);
+	spin_unlock_irqrestore(&ctx->completion_lock, flags);
+}
+
+static void io_fill_cq_error(struct io_ring_ctx *ctx, struct sqe_submit *s,
+			     long error)
+{
+	io_cqring_fill_event(ctx, s->index, error, 0);
+
+	if (waitqueue_active(&ctx->wait))
+		wake_up(&ctx->wait);
+}
+
+static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx)
+{
+	struct io_kiocb *req;
+
+	if (!percpu_ref_tryget(&ctx->refs))
+		return NULL;
+
+	req = kmem_cache_alloc(req_cachep, GFP_ATOMIC | __GFP_NOWARN);
+	if (!req)
+		return NULL;
+
+	req->ctx = ctx;
+	INIT_LIST_HEAD(&req->list);
+	req->flags = 0;
+	return req;
+}
+
+static void io_ring_drop_ctx_refs(struct io_ring_ctx *ctx, unsigned refs)
+{
+	percpu_ref_put_many(&ctx->refs, refs);
+
+	if (waitqueue_active(&ctx->wait))
+		wake_up(&ctx->wait);
+}
+
+static void io_free_req(struct io_kiocb *req)
+{
+	kmem_cache_free(req_cachep, req);
+	io_ring_drop_ctx_refs(req->ctx, 1);
+}
+
+static void kiocb_end_write(struct kiocb *kiocb)
+{
+	if (kiocb->ki_flags & IOCB_WRITE) {
+		struct inode *inode = file_inode(kiocb->ki_filp);
+
+		/*
+		 * Tell lockdep we inherited freeze protection from submission
+		 * thread.
+		 */
+		if (S_ISREG(inode->i_mode))
+			__sb_writers_acquired(inode->i_sb, SB_FREEZE_WRITE);
+		file_end_write(kiocb->ki_filp);
+	}
+}
+
+static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
+{
+	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
+
+	kiocb_end_write(kiocb);
+
+	fput(kiocb->ki_filp);
+	io_cqring_fill_event(req->ctx, req->user_data, res, 0);
+	io_free_req(req);
+}
+
+static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+		      bool force_nonblock)
+{
+	struct kiocb *kiocb = &req->rw;
+	int ret;
+
+	kiocb->ki_filp = fget(sqe->fd);
+	if (unlikely(!kiocb->ki_filp))
+		return -EBADF;
+	kiocb->ki_pos = sqe->off;
+	kiocb->ki_flags = iocb_flags(kiocb->ki_filp);
+	kiocb->ki_hint = ki_hint_validate(file_write_hint(kiocb->ki_filp));
+	if (sqe->ioprio) {
+		ret = ioprio_check_cap(sqe->ioprio);
+		if (ret)
+			goto out_fput;
+
+		kiocb->ki_ioprio = sqe->ioprio;
+	} else
+		kiocb->ki_ioprio = get_current_ioprio();
+
+	ret = kiocb_set_rw_flags(kiocb, sqe->rw_flags);
+	if (unlikely(ret))
+		goto out_fput;
+	if (force_nonblock) {
+		kiocb->ki_flags |= IOCB_NOWAIT;
+		req->flags |= REQ_F_FORCE_NONBLOCK;
+	}
+	if (kiocb->ki_flags & IOCB_HIPRI) {
+		ret = -EINVAL;
+		goto out_fput;
+	}
+
+	kiocb->ki_complete = io_complete_rw;
+	return 0;
+out_fput:
+	fput(kiocb->ki_filp);
+	return ret;
+}
+
+static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
+{
+	switch (ret) {
+	case -EIOCBQUEUED:
+		break;
+	case -ERESTARTSYS:
+	case -ERESTARTNOINTR:
+	case -ERESTARTNOHAND:
+	case -ERESTART_RESTARTBLOCK:
+		/*
+		 * There's no easy way to restart the syscall since other AIO's
+		 * may be already running. Just fail this IO with EINTR.
+		 */
+		ret = -EINTR;
+		/*FALLTHRU*/
+	default:
+		kiocb->ki_complete(kiocb, ret, 0);
+	}
+}
+
+static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
+			   const struct io_uring_sqe *sqe,
+			   struct iovec **iovec, struct iov_iter *iter)
+{
+	void __user *buf = (void __user *) (uintptr_t) sqe->addr;
+
+#ifdef CONFIG_COMPAT
+	if (ctx->compat)
+		return compat_import_iovec(rw, buf, sqe->len, UIO_FASTIOV,
+						iovec, iter);
+#endif
+	return import_iovec(rw, buf, sqe->len, UIO_FASTIOV, iovec, iter);
+}
+
+static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+		       bool force_nonblock)
+{
+	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
+	struct kiocb *kiocb = &req->rw;
+	struct iov_iter iter;
+	struct file *file;
+	ssize_t ret;
+
+	ret = io_prep_rw(req, sqe, force_nonblock);
+	if (ret)
+		return ret;
+	file = kiocb->ki_filp;
+
+	ret = -EBADF;
+	if (unlikely(!(file->f_mode & FMODE_READ)))
+		goto out_fput;
+	ret = -EINVAL;
+	if (unlikely(!file->f_op->read_iter))
+		goto out_fput;
+
+	ret = io_import_iovec(req->ctx, READ, sqe, &iovec, &iter);
+	if (ret)
+		goto out_fput;
+
+	ret = rw_verify_area(READ, file, &kiocb->ki_pos, iov_iter_count(&iter));
+	if (!ret) {
+		ssize_t ret2;
+
+		/* Catch -EAGAIN return for forced non-blocking submission */
+		ret2 = call_read_iter(file, kiocb, &iter);
+		if (!force_nonblock || ret2 != -EAGAIN)
+			io_rw_done(kiocb, ret2);
+		else
+			ret = -EAGAIN;
+	}
+	kfree(iovec);
+out_fput:
+	if (unlikely(ret))
+		fput(file);
+	return ret;
+}
+
+static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+			bool force_nonblock)
+{
+	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
+	struct kiocb *kiocb = &req->rw;
+	struct iov_iter iter;
+	struct file *file;
+	ssize_t ret;
+
+	ret = io_prep_rw(req, sqe, force_nonblock);
+	if (ret)
+		return ret;
+	file = kiocb->ki_filp;
+
+	ret = -EAGAIN;
+	if (force_nonblock && !(kiocb->ki_flags & IOCB_DIRECT))
+		goto out_fput;
+
+	ret = -EBADF;
+	if (unlikely(!(file->f_mode & FMODE_WRITE)))
+		goto out_fput;
+	ret = -EINVAL;
+	if (unlikely(!file->f_op->write_iter))
+		goto out_fput;
+
+	ret = io_import_iovec(req->ctx, WRITE, sqe, &iovec, &iter);
+	if (ret)
+		goto out_fput;
+
+	ret = rw_verify_area(WRITE, file, &kiocb->ki_pos,
+				iov_iter_count(&iter));
+	if (!ret) {
+		/*
+		 * Open-code file_start_write here to grab freeze protection,
+		 * which will be released by another thread in
+		 * io_complete_rw().  Fool lockdep by telling it the lock got
+		 * released so that it doesn't complain about the held lock when
+		 * we return to userspace.
+		 */
+		if (S_ISREG(file_inode(file)->i_mode)) {
+			__sb_start_write(file_inode(file)->i_sb,
+						SB_FREEZE_WRITE, true);
+			__sb_writers_release(file_inode(file)->i_sb,
+						SB_FREEZE_WRITE);
+		}
+		kiocb->ki_flags |= IOCB_WRITE;
+		io_rw_done(kiocb, call_write_iter(file, kiocb, &iter));
+	}
+out_fput:
+	if (unlikely(ret))
+		fput(file);
+	return ret;
+}
+
+/*
+ * IORING_OP_NOP just posts a completion event, nothing else.
+ */
+static int io_nop(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+
+	__io_cqring_fill_event(ctx, sqe->user_data, 0, 0);
+	io_free_req(req);
+	return 0;
+}
+
+static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
+			   struct sqe_submit *s, bool force_nonblock)
+{
+	const struct io_uring_sqe *sqe = s->sqe;
+	ssize_t ret;
+
+	/* enforce forwards compatibility on users */
+	if (unlikely(sqe->flags))
+		return -EINVAL;
+
+	if (unlikely(s->index >= ctx->sq_entries))
+		return -EINVAL;
+	req->user_data = sqe->user_data;
+
+	ret = -EINVAL;
+	switch (sqe->opcode) {
+	case IORING_OP_NOP:
+		ret = io_nop(req, sqe);
+		break;
+	case IORING_OP_READV:
+		ret = io_read(req, sqe, force_nonblock);
+		break;
+	case IORING_OP_WRITEV:
+		ret = io_write(req, sqe, force_nonblock);
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	return ret;
+}
+
+static void io_sq_wq_submit_work(struct work_struct *work)
+{
+	struct io_kiocb *req = container_of(work, struct io_kiocb, work.work);
+	struct io_ring_ctx *ctx = req->ctx;
+	mm_segment_t old_fs = get_fs();
+	struct files_struct *old_files;
+	int ret;
+
+	/*
+	 * Ensure we clear previously set flags. even it NOWAIT was originally
+	 * set, it's pointless now that we're in an async context.
+	 */
+	req->rw.ki_flags &= ~IOCB_NOWAIT;
+	req->flags &= ~REQ_F_FORCE_NONBLOCK;
+
+	old_files = current->files;
+	current->files = ctx->sqo_files;
+
+	if (!mmget_not_zero(ctx->sqo_mm)) {
+		ret = -EFAULT;
+		goto err;
+	}
+
+	use_mm(ctx->sqo_mm);
+	set_fs(USER_DS);
+
+	ret = __io_submit_sqe(ctx, req, &req->work.submit, false);
+
+	set_fs(old_fs);
+	unuse_mm(ctx->sqo_mm);
+	mmput(ctx->sqo_mm);
+err:
+	if (ret) {
+		io_fill_cq_error(ctx, &req->work.submit, ret);
+		io_free_req(req);
+	}
+	current->files = old_files;
+}
+
+static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s)
+{
+	struct io_kiocb *req;
+	ssize_t ret;
+
+	req = io_get_req(ctx);
+	if (unlikely(!req))
+		return -EAGAIN;
+
+	ret = __io_submit_sqe(ctx, req, s, true);
+	if (ret == -EAGAIN) {
+		memcpy(&req->work.submit, s, sizeof(*s));
+		INIT_WORK(&req->work.work, io_sq_wq_submit_work);
+		queue_work(ctx->sqo_wq, &req->work.work);
+		ret = 0;
+	}
+	if (ret)
+		io_free_req(req);
+
+	return ret;
+}
+
+static void io_inc_sqring(struct io_ring_ctx *ctx)
+{
+	struct io_sq_ring *ring = ctx->sq_ring;
+
+	ring->r.head++;
+	smp_wmb();
+}
+
+static bool io_peek_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
+{
+	struct io_sq_ring *ring = ctx->sq_ring;
+	unsigned head;
+
+	smp_rmb();
+	head = READ_ONCE(ring->r.head);
+	if (head == READ_ONCE(ring->r.tail))
+		return false;
+
+	head = ring->array[head & ctx->sq_mask];
+	if (head < ctx->sq_entries) {
+		s->index = head;
+		s->sqe = &ctx->sq_sqes[head];
+		return true;
+	}
+
+	/* drop invalid entries */
+	ring->r.head++;
+	ring->dropped++;
+	smp_wmb();
+	return false;
+}
+
+static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
+{
+	int i, ret = 0, submit = 0;
+	struct blk_plug plug;
+
+	if (to_submit > IO_PLUG_THRESHOLD)
+		blk_start_plug(&plug);
+
+	for (i = 0; i < to_submit; i++) {
+		struct sqe_submit s;
+
+		if (!io_peek_sqring(ctx, &s))
+			break;
+
+		ret = io_submit_sqe(ctx, &s);
+		if (ret)
+			break;
+
+		submit++;
+		io_inc_sqring(ctx);
+	}
+
+	if (to_submit > IO_PLUG_THRESHOLD)
+		blk_finish_plug(&plug);
+
+	return submit ? submit : ret;
+}
+
+/*
+ * Wait until events become available, if we don't already have some. The
+ * application must reap them itself, as they reside on the shared cq ring.
+ */
+static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events)
+{
+	struct io_cq_ring *ring = ctx->cq_ring;
+	DEFINE_WAIT(wait);
+	int ret = 0;
+
+	smp_rmb();
+	if (ring->r.head != ring->r.tail)
+		return 0;
+	if (!min_events)
+		return 0;
+
+	do {
+		prepare_to_wait(&ctx->wait, &wait, TASK_INTERRUPTIBLE);
+
+		ret = 0;
+		smp_rmb();
+		if (ring->r.head != ring->r.tail)
+			break;
+
+		schedule();
+
+		ret = -EINTR;
+		if (signal_pending(current))
+			break;
+	} while (1);
+
+	finish_wait(&ctx->wait, &wait);
+	return ring->r.head == ring->r.tail ? ret : 0;
+}
+
+static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
+			    unsigned min_complete, unsigned flags)
+{
+	int ret = 0;
+
+	if (to_submit) {
+		ret = io_ring_submit(ctx, to_submit);
+		if (ret < 0)
+			return ret;
+	}
+	if (flags & IORING_ENTER_GETEVENTS) {
+		int get_ret;
+
+		if (!ret && to_submit)
+			min_complete = 0;
+
+		get_ret = io_cqring_wait(ctx, min_complete);
+		if (get_ret < 0 && !ret)
+			ret = get_ret;
+	}
+
+	return ret;
+}
+
+static int io_sq_offload_start(struct io_ring_ctx *ctx)
+{
+	int ret;
+
+	ctx->sqo_mm = current->mm;
+
+	/*
+	 * This is safe since 'current' has the fd installed, and if that
+	 * gets closed on exit, then fops->release() is invoked which
+	 * waits for the sq thread and sq workqueue to flush and exit
+	 * before exiting.
+	 */
+	ret = -EBADF;
+	ctx->sqo_files = current->files;
+	if (!ctx->sqo_files)
+		goto err;
+
+	/* Do QD, or 2 * CPUS, whatever is smallest */
+	ctx->sqo_wq = alloc_workqueue("io_ring-wq", WQ_UNBOUND | WQ_FREEZABLE,
+			min(ctx->sq_entries - 1, 2 * num_online_cpus()));
+	if (!ctx->sqo_wq) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
+	return 0;
+err:
+	if (ctx->sqo_files)
+		ctx->sqo_files = NULL;
+	ctx->sqo_mm = NULL;
+	return ret;
+}
+
+static void io_sq_offload_stop(struct io_ring_ctx *ctx)
+{
+	if (ctx->sqo_wq) {
+		destroy_workqueue(ctx->sqo_wq);
+		ctx->sqo_wq = NULL;
+	}
+}
+
+static void io_free_scq_urings(struct io_ring_ctx *ctx)
+{
+	if (ctx->sq_ring) {
+		page_frag_free(ctx->sq_ring);
+		ctx->sq_ring = NULL;
+	}
+	if (ctx->sq_sqes) {
+		page_frag_free(ctx->sq_sqes);
+		ctx->sq_sqes = NULL;
+	}
+	if (ctx->cq_ring) {
+		page_frag_free(ctx->cq_ring);
+		ctx->cq_ring = NULL;
+	}
+}
+
+static void io_ring_ctx_free(struct io_ring_ctx *ctx)
+{
+	io_sq_offload_stop(ctx);
+	io_free_scq_urings(ctx);
+	percpu_ref_exit(&ctx->refs);
+	kfree(ctx);
+}
+
+static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
+{
+	mutex_lock(&ctx->uring_lock);
+	percpu_ref_kill(&ctx->refs);
+	mutex_unlock(&ctx->uring_lock);
+
+	wait_for_completion(&ctx->ctx_done);
+	io_ring_ctx_free(ctx);
+}
+
+static int io_uring_release(struct inode *inode, struct file *file)
+{
+	struct io_ring_ctx *ctx = file->private_data;
+
+	file->private_data = NULL;
+	io_ring_ctx_wait_and_kill(ctx);
+	return 0;
+}
+
+static int io_uring_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	loff_t offset = (loff_t) vma->vm_pgoff << PAGE_SHIFT;
+	unsigned long sz = vma->vm_end - vma->vm_start;
+	struct io_ring_ctx *ctx = file->private_data;
+	unsigned long pfn;
+	struct page *page;
+	void *ptr;
+
+	switch (offset) {
+	case IORING_OFF_SQ_RING:
+		ptr = ctx->sq_ring;
+		break;
+	case IORING_OFF_SQES:
+		ptr = ctx->sq_sqes;
+		break;
+	case IORING_OFF_CQ_RING:
+		ptr = ctx->cq_ring;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	page = virt_to_head_page(ptr);
+	if (sz > (PAGE_SIZE << compound_order(page)))
+		return -EINVAL;
+
+	pfn = virt_to_phys(ptr) >> PAGE_SHIFT;
+	return remap_pfn_range(vma, vma->vm_start, pfn, sz, vma->vm_page_prot);
+}
+
+SYSCALL_DEFINE4(io_uring_enter, unsigned int, fd, u32, to_submit,
+		u32, min_complete, u32, flags)
+{
+	struct io_ring_ctx *ctx;
+	long ret = -EBADF;
+	struct fd f;
+
+	f = fdget(fd);
+	if (!f.file)
+		return -EBADF;
+
+	ret = -EOPNOTSUPP;
+	if (f.file->f_op != &io_uring_fops)
+		goto out_fput;
+
+	ret = -EINVAL;
+	ctx = f.file->private_data;
+	if (!percpu_ref_tryget(&ctx->refs))
+		goto out_fput;
+
+	ret = -EBUSY;
+	if (mutex_trylock(&ctx->uring_lock)) {
+		ret = __io_uring_enter(ctx, to_submit, min_complete, flags);
+		mutex_unlock(&ctx->uring_lock);
+	}
+	io_ring_drop_ctx_refs(ctx, 1);
+out_fput:
+	fdput(f);
+	return ret;
+}
+
+static const struct file_operations io_uring_fops = {
+	.release	= io_uring_release,
+	.mmap		= io_uring_mmap,
+};
+
+static void *io_mem_alloc(size_t size)
+{
+	gfp_t gfp_flags = GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN | __GFP_COMP |
+				__GFP_NORETRY;
+
+	return (void *) __get_free_pages(gfp_flags, get_order(size));
+}
+
+static int io_allocate_scq_urings(struct io_ring_ctx *ctx,
+				  struct io_uring_params *p)
+{
+	struct io_sq_ring *sq_ring;
+	struct io_cq_ring *cq_ring;
+	size_t size;
+	int ret;
+
+	sq_ring = io_mem_alloc(struct_size(sq_ring, array, p->sq_entries));
+	if (!sq_ring)
+		return -ENOMEM;
+
+	ctx->sq_ring = sq_ring;
+	sq_ring->ring_mask = p->sq_entries - 1;
+	sq_ring->ring_entries = p->sq_entries;
+	ctx->sq_mask = sq_ring->ring_mask;
+	ctx->sq_entries = sq_ring->ring_entries;
+
+	ret = -EOVERFLOW;
+	size = array_size(sizeof(struct io_uring_sqe), p->sq_entries);
+	if (size == SIZE_MAX)
+		goto err;
+	ret = -ENOMEM;
+	ctx->sq_sqes = io_mem_alloc(size);
+	if (!ctx->sq_sqes)
+		goto err;
+
+	cq_ring = io_mem_alloc(struct_size(cq_ring, cqes, p->cq_entries));
+	if (!cq_ring)
+		goto err;
+
+	ctx->cq_ring = cq_ring;
+	cq_ring->ring_mask = p->cq_entries - 1;
+	cq_ring->ring_entries = p->cq_entries;
+	ctx->cq_mask = cq_ring->ring_mask;
+	ctx->cq_entries = cq_ring->ring_entries;
+	return 0;
+err:
+	io_free_scq_urings(ctx);
+	return ret;
+}
+
+static void io_fill_offsets(struct io_uring_params *p)
+{
+	memset(&p->sq_off, 0, sizeof(p->sq_off));
+	p->sq_off.head = offsetof(struct io_sq_ring, r.head);
+	p->sq_off.tail = offsetof(struct io_sq_ring, r.tail);
+	p->sq_off.ring_mask = offsetof(struct io_sq_ring, ring_mask);
+	p->sq_off.ring_entries = offsetof(struct io_sq_ring, ring_entries);
+	p->sq_off.flags = offsetof(struct io_sq_ring, flags);
+	p->sq_off.dropped = offsetof(struct io_sq_ring, dropped);
+	p->sq_off.array = offsetof(struct io_sq_ring, array);
+
+	memset(&p->cq_off, 0, sizeof(p->cq_off));
+	p->cq_off.head = offsetof(struct io_cq_ring, r.head);
+	p->cq_off.tail = offsetof(struct io_cq_ring, r.tail);
+	p->cq_off.ring_mask = offsetof(struct io_cq_ring, ring_mask);
+	p->cq_off.ring_entries = offsetof(struct io_cq_ring, ring_entries);
+	p->cq_off.overflow = offsetof(struct io_cq_ring, overflow);
+	p->cq_off.cqes = offsetof(struct io_cq_ring, cqes);
+}
+
+static int io_uring_create(unsigned entries, struct io_uring_params *p,
+			   bool compat)
+{
+	struct io_ring_ctx *ctx;
+	int ret;
+
+	/*
+	 * Use twice as many entries for the CQ ring. It's possible for the
+	 * application to drive a higher depth than the size of the SQ ring,
+	 * since the sqes are only used at submission time. This allows for
+	 * some flexibility in overcommitting a bit.
+	 */
+	p->sq_entries = roundup_pow_of_two(entries);
+	p->cq_entries = 2 * p->sq_entries;
+
+	ctx = io_ring_ctx_alloc(p);
+	if (!ctx)
+		return -ENOMEM;
+	ctx->compat = compat;
+
+	ret = io_allocate_scq_urings(ctx, p);
+	if (ret)
+		goto err;
+
+	ret = io_sq_offload_start(ctx);
+	if (ret)
+		goto err;
+
+	ret = anon_inode_getfd("[io_uring]", &io_uring_fops, ctx,
+				O_RDWR | O_CLOEXEC);
+	if (ret < 0)
+		goto err;
+
+	io_fill_offsets(p);
+	return ret;
+err:
+	io_ring_ctx_wait_and_kill(ctx);
+	return ret;
+}
+
+/*
+ * Sets up an aio uring context, and returns the fd. Applications asks for a
+ * ring size, we return the actual sq/cq ring sizes (among other things) in the
+ * params structure passed in.
+ */
+static long io_uring_setup(u32 entries, struct io_uring_params __user *params,
+			   bool compat)
+{
+	struct io_uring_params p;
+	long ret;
+	int i;
+
+	if (copy_from_user(&p, params, sizeof(p)))
+		return -EFAULT;
+	for (i = 0; i < ARRAY_SIZE(p.resv); i++) {
+		if (p.resv[i])
+			return -EINVAL;
+	}
+
+	if (p.flags)
+		return -EINVAL;
+
+	ret = io_uring_create(entries, &p, compat);
+	if (ret < 0)
+		return ret;
+
+	if (copy_to_user(params, &p, sizeof(p)))
+		return -EFAULT;
+
+	return ret;
+}
+
+SYSCALL_DEFINE2(io_uring_setup, u32, entries,
+		struct io_uring_params __user *, params)
+{
+	return io_uring_setup(entries, params, false);
+}
+
+#ifdef CONFIG_COMPAT
+COMPAT_SYSCALL_DEFINE2(io_uring_setup, u32, entries,
+		       struct io_uring_params __user *, params)
+{
+	return io_uring_setup(entries, params, true);
+}
+#endif
+
+static int __init io_uring_init(void)
+{
+	req_cachep = KMEM_CACHE(io_kiocb, SLAB_HWCACHE_ALIGN | SLAB_PANIC);
+	return 0;
+};
+__initcall(io_uring_init);
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 257cccba3062..542757a4c898 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -69,6 +69,7 @@ struct file_handle;
 struct sigaltstack;
 struct rseq;
 union bpf_attr;
+struct io_uring_params;
 
 #include <linux/types.h>
 #include <linux/aio_abi.h>
@@ -309,6 +310,10 @@ asmlinkage long sys_io_pgetevents_time32(aio_context_t ctx_id,
 				struct io_event __user *events,
 				struct old_timespec32 __user *timeout,
 				const struct __aio_sigset *sig);
+asmlinkage long sys_io_uring_setup(u32 entries,
+				struct io_uring_params __user *p);
+asmlinkage long sys_io_uring_enter(unsigned int fd, u32 to_submit,
+				u32 min_complete, u32 flags);
 
 /* fs/xattr.c */
 asmlinkage long sys_setxattr(const char __user *path, const char __user *name,
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
new file mode 100644
index 000000000000..a1ebaa09e1b8
--- /dev/null
+++ b/include/uapi/linux/io_uring.h
@@ -0,0 +1,97 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Header file for the io_uring interface.
+ *
+ * Copyright (C) 2019 Jens Axboe
+ * Copyright (C) 2019 Christoph Hellwig
+ */
+#ifndef LINUX_IO_URING_H
+#define LINUX_IO_URING_H
+
+#include <linux/fs.h>
+#include <linux/types.h>
+
+/*
+ * IO submission data structure (Submission Queue Entry)
+ */
+struct io_uring_sqe {
+	__u8	opcode;		/* type of operation for this sqe */
+	__u8	flags;		/* as of now unused */
+	__u16	ioprio;		/* ioprio for the request */
+	__s32	fd;		/* file descriptor to do IO on */
+	__u64	off;		/* offset into file */
+	union {
+		void	*addr;	/* buffer or iovecs */
+		__u64	__pad;
+	};
+	__u32	len;		/* buffer size or number of iovecs */
+	union {
+		__kernel_rwf_t	rw_flags;
+		__u32		__resv;
+	};
+	__u64	user_data;	/* data to be passed back at completion time */
+	__u64	__pad2[3];
+};
+
+#define IORING_OP_NOP		0
+#define IORING_OP_READV		1
+#define IORING_OP_WRITEV	2
+
+/*
+ * IO completion data structure (Completion Queue Entry)
+ */
+struct io_uring_cqe {
+	__u64	user_data;	/* sqe->data submission passed back */
+	__s32	res;		/* result code for this event */
+	__u32	flags;
+};
+
+/*
+ * Magic offsets for the application to mmap the data it needs
+ */
+#define IORING_OFF_SQ_RING		0ULL
+#define IORING_OFF_CQ_RING		0x8000000ULL
+#define IORING_OFF_SQES			0x10000000ULL
+
+/*
+ * Filled with the offset for mmap(2)
+ */
+struct io_sqring_offsets {
+	__u32 head;
+	__u32 tail;
+	__u32 ring_mask;
+	__u32 ring_entries;
+	__u32 flags;
+	__u32 dropped;
+	__u32 array;
+	__u32 resv[3];
+};
+
+struct io_cqring_offsets {
+	__u32 head;
+	__u32 tail;
+	__u32 ring_mask;
+	__u32 ring_entries;
+	__u32 overflow;
+	__u32 cqes;
+	__u32 resv[4];
+};
+
+/*
+ * io_uring_enter(2) flags
+ */
+#define IORING_ENTER_GETEVENTS	(1 << 0)
+
+/*
+ * Passed in for io_uring_setup(2). Copied back with updated info on success
+ */
+struct io_uring_params {
+	__u32 sq_entries;
+	__u32 cq_entries;
+	__u32 flags;
+	__u16 resv[10];
+	struct io_sqring_offsets sq_off;
+	struct io_cqring_offsets cq_off;
+};
+
+#endif
diff --git a/init/Kconfig b/init/Kconfig
index d47cb77a220e..ce7bd7af9312 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1402,6 +1402,15 @@ config AIO
 	  by some high performance threaded applications. Disabling
 	  this option saves about 7k.
 
+config IO_URING
+	bool "Enable IO uring support" if EXPERT
+	select ANON_INODES
+	default y
+	help
+	  This option enables support for the io_uring interface, enabling
+	  applications to submit and completion IO through submission and
+	  completion rings that are shared between the kernel and application.
+
 config ADVISE_SYSCALLS
 	bool "Enable madvise/fadvise syscalls" if EXPERT
 	default y
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index ab9d0e3c6d50..ee5e523564bb 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -46,6 +46,8 @@ COND_SYSCALL(io_getevents);
 COND_SYSCALL(io_pgetevents);
 COND_SYSCALL_COMPAT(io_getevents);
 COND_SYSCALL_COMPAT(io_pgetevents);
+COND_SYSCALL(io_uring_setup);
+COND_SYSCALL(io_uring_enter);
 
 /* fs/xattr.c */
 
-- 
2.17.1

[PATCH 06/16] io_uring: add fsync support

[Jens Axboe]

From: Christoph Hellwig <hch@lst.de>

Add a new fsync opcode, which either syncs a range if one is passed,
or the whole file if the offset and length fields are both cleared
to zero.  A flag is provided to use fdatasync semantics, that is only
force out metadata which is required to retrieve the file data, but
not others like metadata.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 33 +++++++++++++++++++++++++++++++++
 include/uapi/linux/io_uring.h |  8 +++++++-
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 148eb3af7dc4..7d74463217a6 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -449,6 +449,36 @@ static int io_nop(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	return 0;
 }
 
+static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+		    bool force_nonblock)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	loff_t end = sqe->off + sqe->len;
+	struct file *file;
+	int ret;
+
+	/* fsync always requires a blocking context */
+	if (force_nonblock)
+		return -EAGAIN;
+
+	if (unlikely(sqe->addr))
+		return -EINVAL;
+	if (unlikely(sqe->fsync_flags & ~IORING_FSYNC_DATASYNC))
+		return -EINVAL;
+
+	file = fget(sqe->fd);
+	if (unlikely(!file))
+		return -EBADF;
+
+	ret = vfs_fsync_range(file, sqe->off, end > 0 ? end : LLONG_MAX,
+			sqe->fsync_flags & IORING_FSYNC_DATASYNC);
+
+	fput(file);
+	io_cqring_fill_event(ctx, sqe->user_data, ret, 0);
+	io_free_req(req);
+	return 0;
+}
+
 static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 			   struct sqe_submit *s, bool force_nonblock)
 {
@@ -474,6 +504,9 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	case IORING_OP_WRITEV:
 		ret = io_write(req, sqe, force_nonblock);
 		break;
+	case IORING_OP_FSYNC:
+		ret = io_fsync(req, sqe, force_nonblock);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index a1ebaa09e1b8..ac49bd179ed9 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -27,7 +27,7 @@ struct io_uring_sqe {
 	__u32	len;		/* buffer size or number of iovecs */
 	union {
 		__kernel_rwf_t	rw_flags;
-		__u32		__resv;
+		__u32		fsync_flags;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
 	__u64	__pad2[3];
@@ -36,6 +36,12 @@ struct io_uring_sqe {
 #define IORING_OP_NOP		0
 #define IORING_OP_READV		1
 #define IORING_OP_WRITEV	2
+#define IORING_OP_FSYNC		3
+
+/*
+ * sqe->fsync_flags
+ */
+#define IORING_FSYNC_DATASYNC	(1 << 0)
 
 /*
  * IO completion data structure (Completion Queue Entry)
-- 
2.17.1

[PATCH 07/16] io_uring: support for IO polling

[Jens Axboe]

Add support for a polled io_uring context. When a read or write is
submitted to a polled context, the application must poll for completions
on the CQ ring through io_uring_enter(2). Polled IO may not generate
IRQ completions, hence they need to be actively found by the application
itself.

To use polling, io_uring_setup() must be used with the
IORING_SETUP_IOPOLL flag being set. It is illegal to mix and match
polled and non-polled IO on an io_uring.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 253 ++++++++++++++++++++++++++++++++--
 include/uapi/linux/io_uring.h |   5 +
 2 files changed, 250 insertions(+), 8 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 7d74463217a6..fb1b04ccc12a 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -56,6 +56,11 @@ struct io_cq_ring {
 	struct io_uring_cqe	cqes[];
 };
 
+struct list_multi {
+	struct list_head list;
+	unsigned multi;
+};
+
 struct io_ring_ctx {
 	struct percpu_ref	refs;
 
@@ -88,6 +93,7 @@ struct io_ring_ctx {
 
 	struct {
 		spinlock_t		completion_lock;
+		struct list_multi	poll_list;
 	} ____cacheline_aligned_in_smp;
 };
 
@@ -111,10 +117,14 @@ struct io_kiocb {
 	struct list_head	list;
 	unsigned long		flags;
 #define REQ_F_FORCE_NONBLOCK	1	/* inline submission attempt */
+#define REQ_F_IOPOLL_COMPLETED	2	/* polled IO has completed */
+#define REQ_F_IOPOLL_EAGAIN	4	/* submission got EAGAIN */
 	u64			user_data;
+	u64			res;
 };
 
 #define IO_PLUG_THRESHOLD		2
+#define IO_IOPOLL_BATCH			8
 
 static struct kmem_cache *req_cachep;
 
@@ -144,6 +154,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	init_completion(&ctx->ctx_done);
 	spin_lock_init(&ctx->completion_lock);
 	init_waitqueue_head(&ctx->wait);
+	INIT_LIST_HEAD(&ctx->poll_list.list);
 	mutex_init(&ctx->uring_lock);
 	return ctx;
 }
@@ -234,12 +245,180 @@ static void io_ring_drop_ctx_refs(struct io_ring_ctx *ctx, unsigned refs)
 		wake_up(&ctx->wait);
 }
 
+static void io_free_req_many(struct io_ring_ctx *ctx, void **reqs, int *nr)
+{
+	if (*nr) {
+		kmem_cache_free_bulk(req_cachep, *nr, reqs);
+		io_ring_drop_ctx_refs(ctx, *nr);
+		*nr = 0;
+	}
+}
+
 static void io_free_req(struct io_kiocb *req)
 {
 	kmem_cache_free(req_cachep, req);
 	io_ring_drop_ctx_refs(req->ctx, 1);
 }
 
+/*
+ * Track whether we have multiple files in our lists. This will impact how
+ * we do polling eventually, not spinning if we're on potentially on different
+ * devices.
+ */
+static void io_multi_list_add(struct io_kiocb *req, struct list_multi *list)
+{
+	if (list_empty(&list->list)) {
+		list->multi = 0;
+	} else if (!list->multi) {
+		struct io_kiocb *list_req;
+
+		list_req = list_first_entry(&list->list, struct io_kiocb, list);
+		if (list_req->rw.ki_filp != req->rw.ki_filp)
+			list->multi = 1;
+	}
+
+	/*
+	 * For fast devices, IO may have already completed. If it has, add
+	 * it to the front so we find it first. We can't add to the poll_done
+	 * list as that's unlocked from the completion side.
+	 */
+	if (req->flags & REQ_F_IOPOLL_COMPLETED)
+		list_add(&req->list, &list->list);
+	else
+		list_add_tail(&req->list, &list->list);
+}
+
+/*
+ * Find and free completed poll iocbs
+ */
+static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
+			       struct list_head *done)
+{
+	void *reqs[IO_IOPOLL_BATCH];
+	struct io_kiocb *req;
+	int to_free = 0;
+
+	while (!list_empty(done)) {
+		req = list_first_entry(done, struct io_kiocb, list);
+		list_del(&req->list);
+
+		__io_cqring_fill_event(ctx, req->user_data, req->res, 0);
+
+		reqs[to_free++] = req;
+		(*nr_events)++;
+
+		fput(req->rw.ki_filp);
+		if (to_free == ARRAY_SIZE(reqs))
+			io_free_req_many(ctx, reqs, &to_free);
+	}
+
+	if (to_free)
+		io_free_req_many(ctx, reqs, &to_free);
+}
+
+static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
+			long min)
+{
+	struct io_kiocb *req, *tmp;
+	int polled, found, ret;
+	LIST_HEAD(done);
+	bool spin;
+
+	/*
+	 * Only spin for completions if we don't have multiple devices hanging
+	 * off our complete list, and we're under the requested amount.
+	 */
+	spin = !ctx->poll_list.multi && (*nr_events < min);
+
+	ret = polled = found = 0;
+	list_for_each_entry_safe(req, tmp, &ctx->poll_list.list, list) {
+		struct kiocb *kiocb = &req->rw;
+
+		if (req->flags & REQ_F_IOPOLL_COMPLETED) {
+			list_move_tail(&req->list, &done);
+			spin = false;
+			continue;
+		}
+
+		ret = kiocb->ki_filp->f_op->iopoll(kiocb, spin);
+		if (ret < 0)
+			break;
+
+		polled += ret;
+		if (polled && spin)
+			spin = false;
+		ret = 0;
+	}
+
+	if (!list_empty(&done))
+		io_iopoll_complete(ctx, nr_events, &done);
+
+	return ret;
+}
+
+/*
+ * Poll for a mininum of 'min' events, and a maximum of 'max'. Note that if
+ * min == 0 we consider that a non-spinning poll check - we'll still enter
+ * the driver poll loop, but only as a non-spinning completion check.
+ */
+static int io_iopoll_getevents(struct io_ring_ctx *ctx, unsigned int *nr_events,
+				long min)
+{
+	int ret;
+
+	do {
+		if (list_empty(&ctx->poll_list.list))
+			return 0;
+
+		ret = io_do_iopoll(ctx, nr_events, min);
+		if (ret < 0)
+			break;
+	} while (min && *nr_events < min);
+
+	if (ret < 0)
+		return ret;
+
+	return *nr_events < min;
+}
+
+/*
+ * We can't just wait for polled events to come to us, we have to actively
+ * find and complete them.
+ */
+static void io_iopoll_reap_events(struct io_ring_ctx *ctx)
+{
+	if (!(ctx->flags & IORING_SETUP_IOPOLL))
+		return;
+
+	mutex_lock(&ctx->uring_lock);
+	while (!list_empty(&ctx->poll_list.list)) {
+		unsigned int nr_events = 0;
+
+		io_iopoll_getevents(ctx, &nr_events, 1);
+	}
+	mutex_unlock(&ctx->uring_lock);
+}
+
+static int io_iopoll_check(struct io_ring_ctx *ctx, unsigned *nr_events,
+			   long min)
+{
+	int ret = 0;
+
+	while (!*nr_events || !need_resched()) {
+		int tmin = 0;
+
+		if (*nr_events < min)
+			tmin = min - *nr_events;
+
+		ret = io_iopoll_getevents(ctx, nr_events, tmin);
+		if (ret <= 0)
+			break;
+		ret = 0;
+	}
+
+	return ret;
+}
+
 static void kiocb_end_write(struct kiocb *kiocb)
 {
 	if (kiocb->ki_flags & IOCB_WRITE) {
@@ -266,9 +445,37 @@ static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
 	io_free_req(req);
 }
 
+static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
+{
+	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
+
+	kiocb_end_write(kiocb);
+
+	if (unlikely(res == -EAGAIN)) {
+		req->flags |= REQ_F_IOPOLL_EAGAIN;
+	} else {
+		req->flags |= REQ_F_IOPOLL_COMPLETED;
+		req->res = res;
+	}
+}
+
+/*
+ * After the iocb has been issued, it's safe to be found on the poll list.
+ * Adding the kiocb to the list AFTER submission ensures that we don't
+ * find it from a io_getevents() thread before the issuer is done accessing
+ * the kiocb cookie.
+ */
+static void io_iopoll_req_issued(struct io_kiocb *req)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+
+	io_multi_list_add(req, &ctx->poll_list);
+}
+
 static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		      bool force_nonblock)
 {
+	struct io_ring_ctx *ctx = req->ctx;
 	struct kiocb *kiocb = &req->rw;
 	int ret;
 
@@ -294,12 +501,21 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		kiocb->ki_flags |= IOCB_NOWAIT;
 		req->flags |= REQ_F_FORCE_NONBLOCK;
 	}
-	if (kiocb->ki_flags & IOCB_HIPRI) {
-		ret = -EINVAL;
-		goto out_fput;
-	}
+	if (ctx->flags & IORING_SETUP_IOPOLL) {
+		ret = -EOPNOTSUPP;
+		if (!(kiocb->ki_flags & IOCB_DIRECT) ||
+		    !kiocb->ki_filp->f_op->iopoll)
+			goto out_fput;
 
-	kiocb->ki_complete = io_complete_rw;
+		kiocb->ki_flags |= IOCB_HIPRI;
+		kiocb->ki_complete = io_complete_rw_iopoll;
+	} else {
+		if (kiocb->ki_flags & IOCB_HIPRI) {
+			ret = -EINVAL;
+			goto out_fput;
+		}
+		kiocb->ki_complete = io_complete_rw;
+	}
 	return 0;
 out_fput:
 	fput(kiocb->ki_filp);
@@ -444,6 +660,9 @@ static int io_nop(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
 	struct io_ring_ctx *ctx = req->ctx;
 
+	if (unlikely(ctx->flags & IORING_SETUP_IOPOLL))
+		return -EINVAL;
+
 	__io_cqring_fill_event(ctx, sqe->user_data, 0, 0);
 	io_free_req(req);
 	return 0;
@@ -461,6 +680,8 @@ static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	if (force_nonblock)
 		return -EAGAIN;
 
+	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
+		return -EINVAL;
 	if (unlikely(sqe->addr))
 		return -EINVAL;
 	if (unlikely(sqe->fsync_flags & ~IORING_FSYNC_DATASYNC))
@@ -512,7 +733,16 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 		break;
 	}
 
-	return ret;
+	if (ret)
+		return ret;
+
+	if (ctx->flags & IORING_SETUP_IOPOLL) {
+		if (req->flags & REQ_F_IOPOLL_EAGAIN)
+			return -EAGAIN;
+		io_iopoll_req_issued(req);
+	}
+
+	return 0;
 }
 
 static void io_sq_wq_submit_work(struct work_struct *work)
@@ -682,12 +912,17 @@ static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
 			return ret;
 	}
 	if (flags & IORING_ENTER_GETEVENTS) {
+		unsigned nr_events = 0;
 		int get_ret;
 
 		if (!ret && to_submit)
 			min_complete = 0;
 
-		get_ret = io_cqring_wait(ctx, min_complete);
+		if (ctx->flags & IORING_SETUP_IOPOLL)
+			get_ret = io_iopoll_check(ctx, &nr_events,
+							min_complete);
+		else
+			get_ret = io_cqring_wait(ctx, min_complete);
 		if (get_ret < 0 && !ret)
 			ret = get_ret;
 	}
@@ -755,6 +990,7 @@ static void io_free_scq_urings(struct io_ring_ctx *ctx)
 static void io_ring_ctx_free(struct io_ring_ctx *ctx)
 {
 	io_sq_offload_stop(ctx);
+	io_iopoll_reap_events(ctx);
 	io_free_scq_urings(ctx);
 	percpu_ref_exit(&ctx->refs);
 	kfree(ctx);
@@ -766,6 +1002,7 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
 	percpu_ref_kill(&ctx->refs);
 	mutex_unlock(&ctx->uring_lock);
 
+	io_iopoll_reap_events(ctx);
 	wait_for_completion(&ctx->ctx_done);
 	io_ring_ctx_free(ctx);
 }
@@ -975,7 +1212,7 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params,
 			return -EINVAL;
 	}
 
-	if (p.flags)
+	if (p.flags & ~IORING_SETUP_IOPOLL)
 		return -EINVAL;
 
 	ret = io_uring_create(entries, &p, compat);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index ac49bd179ed9..d31ae2f767d1 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -33,6 +33,11 @@ struct io_uring_sqe {
 	__u64	__pad2[3];
 };
 
+/*
+ * io_uring_setup() flags
+ */
+#define IORING_SETUP_IOPOLL	(1 << 0)	/* io_context is polled */
+
 #define IORING_OP_NOP		0
 #define IORING_OP_READV		1
 #define IORING_OP_WRITEV	2
-- 
2.17.1

[PATCH 08/16] io_uring: add submission side request cache

[Jens Axboe]

We have to add each submitted polled request to the io_ring_ctx
poll_submitted list, which means we have to grab the poll_lock. We
already use the block plug to batch submissions if we're doing a batch
of IO submissions, extend that to cover the poll requests internally as
well.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 121 +++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 106 insertions(+), 15 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index fb1b04ccc12a..62f31f20f3d5 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -126,6 +126,21 @@ struct io_kiocb {
 #define IO_PLUG_THRESHOLD		2
 #define IO_IOPOLL_BATCH			8
 
+struct io_submit_state {
+	struct io_ring_ctx *ctx;
+
+	struct blk_plug plug;
+#ifdef CONFIG_BLOCK
+	struct blk_plug_cb plug_cb;
+#endif
+
+	/*
+	 * Polled iocbs that have been submitted, but not added to the ctx yet
+	 */
+	struct list_multi req_list;
+	unsigned int req_count;
+};
+
 static struct kmem_cache *req_cachep;
 
 static const struct file_operations io_uring_fops;
@@ -288,6 +303,12 @@ static void io_multi_list_add(struct io_kiocb *req, struct list_multi *list)
 		list_add_tail(&req->list, &list->list);
 }
 
+static void io_multi_list_splice(struct list_multi *src, struct list_multi *dst)
+{
+	list_splice_tail_init(&src->list, &dst->list);
+	dst->multi |= src->multi;
+}
+
 /*
  * Find and free completed poll iocbs
  */
@@ -459,17 +480,46 @@ static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
 	}
 }
 
+/*
+ * Called either at the end of IO submission, or through a plug callback
+ * because we're going to schedule. Moves out local batch of requests to
+ * the ctx poll list, so they can be found for polling + reaping.
+ */
+static void io_flush_state_reqs(struct io_ring_ctx *ctx,
+				 struct io_submit_state *state)
+{
+	io_multi_list_splice(&state->req_list, &ctx->poll_list);
+	state->req_count = 0;
+}
+
+static void io_iopoll_req_add_list(struct io_kiocb *req)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+
+	io_multi_list_add(req, &ctx->poll_list);
+}
+
+static void io_iopoll_req_add_state(struct io_submit_state *state,
+				     struct io_kiocb *req)
+{
+	io_multi_list_add(req, &state->req_list);
+	if (++state->req_count >= IO_IOPOLL_BATCH)
+		io_flush_state_reqs(state->ctx, state);
+}
+
 /*
  * After the iocb has been issued, it's safe to be found on the poll list.
  * Adding the kiocb to the list AFTER submission ensures that we don't
  * find it from a io_getevents() thread before the issuer is done accessing
  * the kiocb cookie.
  */
-static void io_iopoll_req_issued(struct io_kiocb *req)
+static void io_iopoll_req_issued(struct io_submit_state *state,
+				 struct io_kiocb *req)
 {
-	struct io_ring_ctx *ctx = req->ctx;
-
-	io_multi_list_add(req, &ctx->poll_list);
+	if (!state || !IS_ENABLED(CONFIG_BLOCK))
+		io_iopoll_req_add_list(req);
+	else
+		io_iopoll_req_add_state(state, req);
 }
 
 static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
@@ -701,7 +751,8 @@ static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 }
 
 static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
-			   struct sqe_submit *s, bool force_nonblock)
+			   struct sqe_submit *s, bool force_nonblock,
+			   struct io_submit_state *state)
 {
 	const struct io_uring_sqe *sqe = s->sqe;
 	ssize_t ret;
@@ -739,7 +790,7 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	if (ctx->flags & IORING_SETUP_IOPOLL) {
 		if (req->flags & REQ_F_IOPOLL_EAGAIN)
 			return -EAGAIN;
-		io_iopoll_req_issued(req);
+		io_iopoll_req_issued(state, req);
 	}
 
 	return 0;
@@ -771,7 +822,7 @@ static void io_sq_wq_submit_work(struct work_struct *work)
 	use_mm(ctx->sqo_mm);
 	set_fs(USER_DS);
 
-	ret = __io_submit_sqe(ctx, req, &req->work.submit, false);
+	ret = __io_submit_sqe(ctx, req, &req->work.submit, false, NULL);
 
 	set_fs(old_fs);
 	unuse_mm(ctx->sqo_mm);
@@ -784,7 +835,8 @@ static void io_sq_wq_submit_work(struct work_struct *work)
 	current->files = old_files;
 }
 
-static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s)
+static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
+			 struct io_submit_state *state)
 {
 	struct io_kiocb *req;
 	ssize_t ret;
@@ -793,7 +845,7 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s)
 	if (unlikely(!req))
 		return -EAGAIN;
 
-	ret = __io_submit_sqe(ctx, req, s, true);
+	ret = __io_submit_sqe(ctx, req, s, true, state);
 	if (ret == -EAGAIN) {
 		memcpy(&req->work.submit, s, sizeof(*s));
 		INIT_WORK(&req->work.work, io_sq_wq_submit_work);
@@ -806,6 +858,43 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s)
 	return ret;
 }
 
+#ifdef CONFIG_BLOCK
+static void io_state_unplug(struct blk_plug_cb *cb, bool from_schedule)
+{
+	struct io_submit_state *state;
+
+	state = container_of(cb, struct io_submit_state, plug_cb);
+	if (!list_empty(&state->req_list.list))
+		io_flush_state_reqs(state->ctx, state);
+}
+#endif
+
+/*
+ * Batched submission is done, ensure local IO is flushed out.
+ */
+static void io_submit_state_end(struct io_submit_state *state)
+{
+	blk_finish_plug(&state->plug);
+	if (!list_empty(&state->req_list.list))
+		io_flush_state_reqs(state->ctx, state);
+}
+
+/*
+ * Start submission side cache.
+ */
+static void io_submit_state_start(struct io_submit_state *state,
+				  struct io_ring_ctx *ctx)
+{
+	state->ctx = ctx;
+	INIT_LIST_HEAD(&state->req_list.list);
+	state->req_count = 0;
+#ifdef CONFIG_BLOCK
+	state->plug_cb.callback = io_state_unplug;
+	blk_start_plug(&state->plug);
+	list_add(&state->plug_cb.list, &state->plug.cb_list);
+#endif
+}
+
 static void io_inc_sqring(struct io_ring_ctx *ctx)
 {
 	struct io_sq_ring *ring = ctx->sq_ring;
@@ -840,11 +929,13 @@ static bool io_peek_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
 
 static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 {
+	struct io_submit_state state, *statep = NULL;
 	int i, ret = 0, submit = 0;
-	struct blk_plug plug;
 
-	if (to_submit > IO_PLUG_THRESHOLD)
-		blk_start_plug(&plug);
+	if (to_submit > IO_PLUG_THRESHOLD) {
+		io_submit_state_start(&state, ctx);
+		statep = &state;
+	}
 
 	for (i = 0; i < to_submit; i++) {
 		struct sqe_submit s;
@@ -852,7 +943,7 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 		if (!io_peek_sqring(ctx, &s))
 			break;
 
-		ret = io_submit_sqe(ctx, &s);
+		ret = io_submit_sqe(ctx, &s, statep);
 		if (ret)
 			break;
 
@@ -860,8 +951,8 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 		io_inc_sqring(ctx);
 	}
 
-	if (to_submit > IO_PLUG_THRESHOLD)
-		blk_finish_plug(&plug);
+	if (statep)
+		io_submit_state_end(statep);
 
 	return submit ? submit : ret;
 }
-- 
2.17.1

[PATCH 09/16] fs: add fget_many() and fput_many()

[Jens Axboe]

Some uses cases repeatedly get and put references to the same file, but
the only exposed interface is doing these one at the time. As each of
these entail an atomic inc or dec on a shared structure, that cost can
add up.

Add fget_many(), which works just like fget(), except it takes an
argument for how many references to get on the file. Ditto fput_many(),
which can drop an arbitrary number of references to a file.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/file.c            | 15 ++++++++++-----
 fs/file_table.c      |  9 +++++++--
 include/linux/file.h |  2 ++
 include/linux/fs.h   |  4 +++-
 4 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/fs/file.c b/fs/file.c
index 3209ee271c41..e0d7ce70e860 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -705,7 +705,7 @@ void do_close_on_exec(struct files_struct *files)
 	spin_unlock(&files->file_lock);
 }
 
-static struct file *__fget(unsigned int fd, fmode_t mask)
+static struct file *__fget(unsigned int fd, fmode_t mask, unsigned int refs)
 {
 	struct files_struct *files = current->files;
 	struct file *file;
@@ -720,7 +720,7 @@ static struct file *__fget(unsigned int fd, fmode_t mask)
 		 */
 		if (file->f_mode & mask)
 			file = NULL;
-		else if (!get_file_rcu(file))
+		else if (!get_file_rcu_many(file, refs))
 			goto loop;
 	}
 	rcu_read_unlock();
@@ -728,15 +728,20 @@ static struct file *__fget(unsigned int fd, fmode_t mask)
 	return file;
 }
 
+struct file *fget_many(unsigned int fd, unsigned int refs)
+{
+	return __fget(fd, FMODE_PATH, refs);
+}
+
 struct file *fget(unsigned int fd)
 {
-	return __fget(fd, FMODE_PATH);
+	return fget_many(fd, 1);
 }
 EXPORT_SYMBOL(fget);
 
 struct file *fget_raw(unsigned int fd)
 {
-	return __fget(fd, 0);
+	return __fget(fd, 0, 1);
 }
 EXPORT_SYMBOL(fget_raw);
 
@@ -767,7 +772,7 @@ static unsigned long __fget_light(unsigned int fd, fmode_t mask)
 			return 0;
 		return (unsigned long)file;
 	} else {
-		file = __fget(fd, mask);
+		file = __fget(fd, mask, 1);
 		if (!file)
 			return 0;
 		return FDPUT_FPUT | (unsigned long)file;
diff --git a/fs/file_table.c b/fs/file_table.c
index 5679e7fcb6b0..155d7514a094 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -326,9 +326,9 @@ void flush_delayed_fput(void)
 
 static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
 
-void fput(struct file *file)
+void fput_many(struct file *file, unsigned int refs)
 {
-	if (atomic_long_dec_and_test(&file->f_count)) {
+	if (atomic_long_sub_and_test(refs, &file->f_count)) {
 		struct task_struct *task = current;
 
 		if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
@@ -347,6 +347,11 @@ void fput(struct file *file)
 	}
 }
 
+void fput(struct file *file)
+{
+	fput_many(file, 1);
+}
+
 /*
  * synchronous analog of fput(); for kernel threads that might be needed
  * in some umount() (and thus can't use flush_delayed_fput() without
diff --git a/include/linux/file.h b/include/linux/file.h
index 6b2fb032416c..3fcddff56bc4 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -13,6 +13,7 @@
 struct file;
 
 extern void fput(struct file *);
+extern void fput_many(struct file *, unsigned int);
 
 struct file_operations;
 struct vfsmount;
@@ -44,6 +45,7 @@ static inline void fdput(struct fd fd)
 }
 
 extern struct file *fget(unsigned int fd);
+extern struct file *fget_many(unsigned int fd, unsigned int refs);
 extern struct file *fget_raw(unsigned int fd);
 extern unsigned long __fdget(unsigned int fd);
 extern unsigned long __fdget_raw(unsigned int fd);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ccb0b7a63aa5..acaad78b6781 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -952,7 +952,9 @@ static inline struct file *get_file(struct file *f)
 	atomic_long_inc(&f->f_count);
 	return f;
 }
-#define get_file_rcu(x) atomic_long_inc_not_zero(&(x)->f_count)
+#define get_file_rcu_many(x, cnt)	\
+	atomic_long_add_unless(&(x)->f_count, (cnt), 0)
+#define get_file_rcu(x) get_file_rcu_many((x), 1)
 #define fput_atomic(x)	atomic_long_add_unless(&(x)->f_count, -1, 1)
 #define file_count(x)	atomic_long_read(&(x)->f_count)
 
-- 
2.17.1

[PATCH 10/16] io_uring: use fget/fput_many() for file references

[Jens Axboe]

On the submission side, add file reference batching to the
io_submit_state. We get as many references as the number of iocbs we
are submitting, and drop unused ones if we end up switching files. The
assumption here is that we're usually only dealing with one fd, and if
there are multiple, hopefuly they are at least somewhat ordered. Could
trivially be extended to cover multiple fds, if needed.

On the completion side we do the same thing, except this is trivially
done just locally in io_iopoll_reap().

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 98 ++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 85 insertions(+), 13 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 62f31f20f3d5..0d7c44a2d424 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -139,6 +139,15 @@ struct io_submit_state {
 	 */
 	struct list_multi req_list;
 	unsigned int req_count;
+
+	/*
+	 * File reference cache
+	 */
+	struct file *file;
+	unsigned int fd;
+	unsigned int has_refs;
+	unsigned int used_refs;
+	unsigned int ios_left;
 };
 
 static struct kmem_cache *req_cachep;
@@ -316,9 +325,11 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 			       struct list_head *done)
 {
 	void *reqs[IO_IOPOLL_BATCH];
+	int file_count, to_free;
+	struct file *file = NULL;
 	struct io_kiocb *req;
-	int to_free = 0;
 
+	file_count = to_free = 0;
 	while (!list_empty(done)) {
 		req = list_first_entry(done, struct io_kiocb, list);
 		list_del(&req->list);
@@ -328,11 +339,27 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 		reqs[to_free++] = req;
 		(*nr_events)++;
 
-		fput(req->rw.ki_filp);
+		/*
+		 * Batched puts of the same file, to avoid dirtying the
+		 * file usage count multiple times, if avoidable.
+		 */
+		if (!file) {
+			file = req->rw.ki_filp;
+			file_count = 1;
+		} else if (file == req->rw.ki_filp) {
+			file_count++;
+		} else {
+			fput_many(file, file_count);
+			file = req->rw.ki_filp;
+			file_count = 1;
+		}
+
 		if (to_free == ARRAY_SIZE(reqs))
 			io_free_req_many(ctx, reqs, &to_free);
 	}
 
+	if (file)
+		fput_many(file, file_count);
 	if (to_free)
 		io_free_req_many(ctx, reqs, &to_free);
 }
@@ -522,14 +549,56 @@ static void io_iopoll_req_issued(struct io_submit_state *state,
 		io_iopoll_req_add_state(state, req);
 }
 
+static void io_file_put(struct io_submit_state *state, struct file *file)
+{
+	if (!state) {
+		fput(file);
+	} else if (state->file) {
+		int diff = state->has_refs - state->used_refs;
+
+		if (diff)
+			fput_many(state->file, diff);
+		state->file = NULL;
+	}
+}
+
+/*
+ * Get as many references to a file as we have IOs left in this submission,
+ * assuming most submissions are for one file, or at least that each file
+ * has more than one submission.
+ */
+static struct file *io_file_get(struct io_submit_state *state, int fd)
+{
+	if (!state)
+		return fget(fd);
+
+	if (state->file) {
+		if (state->fd == fd) {
+			state->used_refs++;
+			state->ios_left--;
+			return state->file;
+		}
+		io_file_put(state, NULL);
+	}
+	state->file = fget_many(fd, state->ios_left);
+	if (!state->file)
+		return NULL;
+
+	state->fd = fd;
+	state->has_refs = state->ios_left;
+	state->used_refs = 1;
+	state->ios_left--;
+	return state->file;
+}
+
 static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
-		      bool force_nonblock)
+		      bool force_nonblock, struct io_submit_state *state)
 {
 	struct io_ring_ctx *ctx = req->ctx;
 	struct kiocb *kiocb = &req->rw;
 	int ret;
 
-	kiocb->ki_filp = fget(sqe->fd);
+	kiocb->ki_filp = io_file_get(state, sqe->fd);
 	if (unlikely(!kiocb->ki_filp))
 		return -EBADF;
 	kiocb->ki_pos = sqe->off;
@@ -568,7 +637,7 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	}
 	return 0;
 out_fput:
-	fput(kiocb->ki_filp);
+	io_file_put(state, kiocb->ki_filp);
 	return ret;
 }
 
@@ -607,7 +676,7 @@ static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
 }
 
 static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
-		       bool force_nonblock)
+		       bool force_nonblock, struct io_submit_state *state)
 {
 	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
 	struct kiocb *kiocb = &req->rw;
@@ -615,7 +684,7 @@ static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	struct file *file;
 	ssize_t ret;
 
-	ret = io_prep_rw(req, sqe, force_nonblock);
+	ret = io_prep_rw(req, sqe, force_nonblock, state);
 	if (ret)
 		return ret;
 	file = kiocb->ki_filp;
@@ -650,7 +719,7 @@ static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 }
 
 static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
-			bool force_nonblock)
+			bool force_nonblock, struct io_submit_state *state)
 {
 	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
 	struct kiocb *kiocb = &req->rw;
@@ -658,7 +727,7 @@ static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	struct file *file;
 	ssize_t ret;
 
-	ret = io_prep_rw(req, sqe, force_nonblock);
+	ret = io_prep_rw(req, sqe, force_nonblock, state);
 	if (ret)
 		return ret;
 	file = kiocb->ki_filp;
@@ -771,10 +840,10 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 		ret = io_nop(req, sqe);
 		break;
 	case IORING_OP_READV:
-		ret = io_read(req, sqe, force_nonblock);
+		ret = io_read(req, sqe, force_nonblock, state);
 		break;
 	case IORING_OP_WRITEV:
-		ret = io_write(req, sqe, force_nonblock);
+		ret = io_write(req, sqe, force_nonblock, state);
 		break;
 	case IORING_OP_FSYNC:
 		ret = io_fsync(req, sqe, force_nonblock);
@@ -877,17 +946,20 @@ static void io_submit_state_end(struct io_submit_state *state)
 	blk_finish_plug(&state->plug);
 	if (!list_empty(&state->req_list.list))
 		io_flush_state_reqs(state->ctx, state);
+	io_file_put(state, NULL);
 }
 
 /*
  * Start submission side cache.
  */
 static void io_submit_state_start(struct io_submit_state *state,
-				  struct io_ring_ctx *ctx)
+				  struct io_ring_ctx *ctx, unsigned max_ios)
 {
 	state->ctx = ctx;
 	INIT_LIST_HEAD(&state->req_list.list);
 	state->req_count = 0;
+	state->file = NULL;
+	state->ios_left = max_ios;
 #ifdef CONFIG_BLOCK
 	state->plug_cb.callback = io_state_unplug;
 	blk_start_plug(&state->plug);
@@ -933,7 +1005,7 @@ static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 	int i, ret = 0, submit = 0;
 
 	if (to_submit > IO_PLUG_THRESHOLD) {
-		io_submit_state_start(&state, ctx);
+		io_submit_state_start(&state, ctx, to_submit);
 		statep = &state;
 	}
 
-- 
2.17.1

[PATCH 11/16] io_uring: batch io_kiocb allocation

[Jens Axboe]

Similarly to how we use the state->ios_left to know how many references
to get to a file, we can use it to allocate the io_kiocb's we need in
bulk.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 66 ++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 50 insertions(+), 16 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 0d7c44a2d424..d0e4e37592fe 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -140,6 +140,13 @@ struct io_submit_state {
 	struct list_multi req_list;
 	unsigned int req_count;
 
+	/*
+	 * io_kiocb alloc cache
+	 */
+	void *reqs[IO_IOPOLL_BATCH];
+	unsigned int free_reqs;
+	unsigned int cur_req;
+
 	/*
 	 * File reference cache
 	 */
@@ -244,29 +251,52 @@ static void io_fill_cq_error(struct io_ring_ctx *ctx, struct sqe_submit *s,
 		wake_up(&ctx->wait);
 }
 
-static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx)
+static void io_ring_drop_ctx_refs(struct io_ring_ctx *ctx, unsigned refs)
 {
+	percpu_ref_put_many(&ctx->refs, refs);
+
+	if (waitqueue_active(&ctx->wait))
+		wake_up(&ctx->wait);
+}
+
+static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx,
+				   struct io_submit_state *state)
+{
+	gfp_t gfp = GFP_ATOMIC | __GFP_NOWARN;
 	struct io_kiocb *req;
 
 	if (!percpu_ref_tryget(&ctx->refs))
 		return NULL;
 
-	req = kmem_cache_alloc(req_cachep, GFP_ATOMIC | __GFP_NOWARN);
-	if (!req)
-		return NULL;
-
-	req->ctx = ctx;
-	INIT_LIST_HEAD(&req->list);
-	req->flags = 0;
-	return req;
-}
+	if (!state)
+		req = kmem_cache_alloc(req_cachep, gfp);
+	else if (!state->free_reqs) {
+		size_t sz;
+		int ret;
+
+		sz = min_t(size_t, state->ios_left, ARRAY_SIZE(state->reqs));
+		ret = kmem_cache_alloc_bulk(req_cachep, gfp, sz,
+						state->reqs);
+		if (ret <= 0)
+			goto out;
+		state->free_reqs = ret - 1;
+		state->cur_req = 1;
+		req = state->reqs[0];
+	} else {
+		req = state->reqs[state->cur_req];
+		state->free_reqs--;
+		state->cur_req++;
+	}
 
-static void io_ring_drop_ctx_refs(struct io_ring_ctx *ctx, unsigned refs)
-{
-	percpu_ref_put_many(&ctx->refs, refs);
+	if (req) {
+		req->ctx = ctx;
+		req->flags = 0;
+		return req;
+	}
 
-	if (waitqueue_active(&ctx->wait))
-		wake_up(&ctx->wait);
+out:
+	io_ring_drop_ctx_refs(ctx, 1);
+	return NULL;
 }
 
 static void io_free_req_many(struct io_ring_ctx *ctx, void **reqs, int *nr)
@@ -910,7 +940,7 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
 	struct io_kiocb *req;
 	ssize_t ret;
 
-	req = io_get_req(ctx);
+	req = io_get_req(ctx, state);
 	if (unlikely(!req))
 		return -EAGAIN;
 
@@ -947,6 +977,9 @@ static void io_submit_state_end(struct io_submit_state *state)
 	if (!list_empty(&state->req_list.list))
 		io_flush_state_reqs(state->ctx, state);
 	io_file_put(state, NULL);
+	if (state->free_reqs)
+		kmem_cache_free_bulk(req_cachep, state->free_reqs,
+					&state->reqs[state->cur_req]);
 }
 
 /*
@@ -958,6 +991,7 @@ static void io_submit_state_start(struct io_submit_state *state,
 	state->ctx = ctx;
 	INIT_LIST_HEAD(&state->req_list.list);
 	state->req_count = 0;
+	state->free_reqs = 0;
 	state->file = NULL;
 	state->ios_left = max_ios;
 #ifdef CONFIG_BLOCK
-- 
2.17.1

[PATCH 12/16] block: implement bio helper to add iter bvec pages to bio

[Jens Axboe]

For an ITER_BVEC, we can just iterate the iov and add the pages
to the bio directly. This requires that the caller doesn't releases
the pages on IO completion, we add a BIO_HOLD_PAGES flag for that.

The current two callers of bio_iov_iter_get_pages() are updated to
check if they need to release pages on completion. This makes them
work with bvecs that contain kernel mapped pages already.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 block/bio.c               | 59 ++++++++++++++++++++++++++++++++-------
 fs/block_dev.c            |  5 ++--
 fs/iomap.c                |  5 ++--
 include/linux/blk_types.h |  1 +
 4 files changed, 56 insertions(+), 14 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 4db1008309ed..7af4f45d2ed6 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -828,6 +828,23 @@ int bio_add_page(struct bio *bio, struct page *page,
 }
 EXPORT_SYMBOL(bio_add_page);
 
+static int __bio_iov_bvec_add_pages(struct bio *bio, struct iov_iter *iter)
+{
+	const struct bio_vec *bv = iter->bvec;
+	unsigned int len;
+	size_t size;
+
+	len = min_t(size_t, bv->bv_len, iter->count);
+	size = bio_add_page(bio, bv->bv_page, len,
+				bv->bv_offset + iter->iov_offset);
+	if (size == len) {
+		iov_iter_advance(iter, size);
+		return 0;
+	}
+
+	return -EINVAL;
+}
+
 #define PAGE_PTRS_PER_BVEC     (sizeof(struct bio_vec) / sizeof(struct page *))
 
 /**
@@ -876,23 +893,43 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 }
 
 /**
- * bio_iov_iter_get_pages - pin user or kernel pages and add them to a bio
+ * bio_iov_iter_get_pages - add user or kernel pages to a bio
  * @bio: bio to add pages to
- * @iter: iov iterator describing the region to be mapped
+ * @iter: iov iterator describing the region to be added
+ *
+ * This takes either an iterator pointing to user memory, or one pointing to
+ * kernel pages (BVEC iterator). If we're adding user pages, we pin them and
+ * map them into the kernel. On IO completion, the caller should put those
+ * pages. If we're adding kernel pages, we just have to add the pages to the
+ * bio directly. We don't grab an extra reference to those pages (the user
+ * should already have that), and we don't put the page on IO completion.
+ * The caller needs to check if the bio is flagged BIO_HOLD_PAGES on IO
+ * completion. If it isn't, then pages should be released.
  *
- * Pins pages from *iter and appends them to @bio's bvec array. The
- * pages will have to be released using put_page() when done.
  * The function tries, but does not guarantee, to pin as many pages as
- * fit into the bio, or are requested in *iter, whatever is smaller.
- * If MM encounters an error pinning the requested pages, it stops.
- * Error is returned only if 0 pages could be pinned.
+ * fit into the bio, or are requested in *iter, whatever is smaller. If
+ * MM encounters an error pinning the requested pages, it stops. Error
+ * is returned only if 0 pages could be pinned.
  */
 int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 {
+	const bool is_bvec = iov_iter_is_bvec(iter);
 	unsigned short orig_vcnt = bio->bi_vcnt;
 
+	/*
+	 * If this is a BVEC iter, then the pages are kernel pages. Don't
+	 * release them on IO completion.
+	 */
+	if (is_bvec)
+		bio_set_flag(bio, BIO_HOLD_PAGES);
+
 	do {
-		int ret = __bio_iov_iter_get_pages(bio, iter);
+		int ret;
+
+		if (is_bvec)
+			ret = __bio_iov_bvec_add_pages(bio, iter);
+		else
+			ret = __bio_iov_iter_get_pages(bio, iter);
 
 		if (unlikely(ret))
 			return bio->bi_vcnt > orig_vcnt ? 0 : ret;
@@ -1634,7 +1671,8 @@ static void bio_dirty_fn(struct work_struct *work)
 		next = bio->bi_private;
 
 		bio_set_pages_dirty(bio);
-		bio_release_pages(bio);
+		if (!bio_flagged(bio, BIO_HOLD_PAGES))
+			bio_release_pages(bio);
 		bio_put(bio);
 	}
 }
@@ -1650,7 +1688,8 @@ void bio_check_pages_dirty(struct bio *bio)
 			goto defer;
 	}
 
-	bio_release_pages(bio);
+	if (!bio_flagged(bio, BIO_HOLD_PAGES))
+		bio_release_pages(bio);
 	bio_put(bio);
 	return;
 defer:
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 2ebd2a0d7789..b7742014c9de 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -324,8 +324,9 @@ static void blkdev_bio_end_io(struct bio *bio)
 		struct bio_vec *bvec;
 		int i;
 
-		bio_for_each_segment_all(bvec, bio, i)
-			put_page(bvec->bv_page);
+		if (!bio_flagged(bio, BIO_HOLD_PAGES))
+			bio_for_each_segment_all(bvec, bio, i)
+				put_page(bvec->bv_page);
 		bio_put(bio);
 	}
 }
diff --git a/fs/iomap.c b/fs/iomap.c
index 4ee50b76b4a1..0a64c9c51203 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -1582,8 +1582,9 @@ static void iomap_dio_bio_end_io(struct bio *bio)
 		struct bio_vec *bvec;
 		int i;
 
-		bio_for_each_segment_all(bvec, bio, i)
-			put_page(bvec->bv_page);
+		if (!bio_flagged(bio, BIO_HOLD_PAGES))
+			bio_for_each_segment_all(bvec, bio, i)
+				put_page(bvec->bv_page);
 		bio_put(bio);
 	}
 }
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 5c7e7f859a24..97e206855cd3 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -215,6 +215,7 @@ struct bio {
 /*
  * bio flags
  */
+#define BIO_HOLD_PAGES	0	/* don't put O_DIRECT pages */
 #define BIO_SEG_VALID	1	/* bi_phys_segments valid */
 #define BIO_CLONED	2	/* doesn't own data */
 #define BIO_BOUNCED	3	/* bio is a bounce bio */
-- 
2.17.1

[PATCH 13/16] io_uring: add support for pre-mapped user IO buffers

[Jens Axboe]

If we have fixed user buffers, we can map them into the kernel when we
setup the io_context. That avoids the need to do get_user_pages() for
each and every IO.

To utilize this feature, the application must call io_uring_register()
after having setup an io_uring context, passing in
IORING_REGISTER_BUFFERS as the opcode, and the following struct as the
argument:

struct io_uring_register_buffers {
	struct iovec *iovecs;
	__u32 nr_iovecs;
};

If successful, these buffers are now mapped into the kernel, eligible
for IO. To use these fixed buffers, the application must use the
IORING_OP_READ_FIXED and IORING_OP_WRITE_FIXED opcodes, and then
set sqe->index to the desired buffer index. sqe->addr..sqe->addr+seq->len
must point to somewhere inside the indexed buffer.

The application may register buffers throughout the lifetime of the
io_uring context. It can call io_uring_register() with
IORING_UNREGISTER_BUFFERS as the opcode to unregister the current set of
buffers, and then register a new set. The application need not
unregister buffers explicitly before shutting down the io_uring context.

It's perfectly valid to setup a larger buffer, and then sometimes only
use parts of it for an IO. As long as the range is within the originally
mapped region, it will work just fine.

RLIMIT_MEMLOCK is used to check how much memory we can pin. A somewhat
arbitrary 1G per buffer size is also imposed.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 arch/x86/entry/syscalls/syscall_32.tbl |   1 +
 arch/x86/entry/syscalls/syscall_64.tbl |   1 +
 fs/io_uring.c                          | 345 ++++++++++++++++++++++++-
 include/linux/sched/user.h             |   2 +-
 include/linux/syscalls.h               |   2 +
 include/uapi/linux/io_uring.h          |  21 +-
 kernel/sys_ni.c                        |   1 +
 7 files changed, 361 insertions(+), 12 deletions(-)

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 194e79c0032e..7e89016f8118 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -400,3 +400,4 @@
 386	i386	rseq			sys_rseq			__ia32_sys_rseq
 387	i386	io_uring_setup		sys_io_uring_setup		__ia32_compat_sys_io_uring_setup
 388	i386	io_uring_enter		sys_io_uring_enter		__ia32_sys_io_uring_enter
+389	i386	io_uring_register	sys_io_uring_register		__ia32_sys_io_uring_register
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 453ff7a79002..8e05d4f05d88 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -345,6 +345,7 @@
 334	common	rseq			__x64_sys_rseq
 335	common	io_uring_setup		__x64_sys_io_uring_setup
 336	common	io_uring_enter		__x64_sys_io_uring_enter
+337	common	io_uring_register	__x64_sys_io_uring_register
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/fs/io_uring.c b/fs/io_uring.c
index d0e4e37592fe..00743a5a6fac 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -24,8 +24,11 @@
 #include <linux/slab.h>
 #include <linux/workqueue.h>
 #include <linux/blkdev.h>
+#include <linux/bvec.h>
 #include <linux/anon_inodes.h>
 #include <linux/sched/mm.h>
+#include <linux/sizes.h>
+#include <linux/nospec.h>
 
 #include <linux/uaccess.h>
 #include <linux/nospec.h>
@@ -61,6 +64,13 @@ struct list_multi {
 	unsigned multi;
 };
 
+struct io_mapped_ubuf {
+	u64		ubuf;
+	size_t		len;
+	struct		bio_vec *bvec;
+	unsigned int	nr_bvecs;
+};
+
 struct io_ring_ctx {
 	struct percpu_ref	refs;
 
@@ -84,6 +94,11 @@ struct io_ring_ctx {
 	struct mm_struct	*sqo_mm;
 	struct files_struct	*sqo_files;
 
+	/* if used, fixed mapped user buffers */
+	unsigned		nr_user_bufs;
+	struct io_mapped_ubuf	*user_bufs;
+	struct user_struct	*user;
+
 	struct completion	ctx_done;
 
 	struct {
@@ -691,12 +706,51 @@ static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
 	}
 }
 
+static int io_import_fixed(struct io_ring_ctx *ctx, int rw,
+			   const struct io_uring_sqe *sqe,
+			   struct iov_iter *iter)
+{
+	struct io_mapped_ubuf *imu;
+	size_t len = sqe->len;
+	size_t offset;
+	int index;
+
+	/* attempt to use fixed buffers without having provided iovecs */
+	if (unlikely(!ctx->user_bufs))
+		return -EFAULT;
+	if (unlikely(sqe->buf_index >= ctx->nr_user_bufs))
+		return -EFAULT;
+
+	index = array_index_nospec(sqe->buf_index, ctx->sq_entries);
+	imu = &ctx->user_bufs[index];
+	if ((unsigned long) sqe->addr < imu->ubuf ||
+	    (unsigned long) sqe->addr + len > imu->ubuf + imu->len)
+		return -EFAULT;
+
+	/*
+	 * May not be a start of buffer, set size appropriately
+	 * and advance us to the beginning.
+	 */
+	offset = (unsigned long) sqe->addr - imu->ubuf;
+	iov_iter_bvec(iter, rw, imu->bvec, imu->nr_bvecs, offset + len);
+	if (offset)
+		iov_iter_advance(iter, offset);
+	return 0;
+}
+
 static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
 			   const struct io_uring_sqe *sqe,
 			   struct iovec **iovec, struct iov_iter *iter)
 {
 	void __user *buf = (void __user *) (uintptr_t) sqe->addr;
 
+	if (sqe->opcode == IORING_OP_READ_FIXED ||
+	    sqe->opcode == IORING_OP_WRITE_FIXED) {
+		ssize_t ret = io_import_fixed(ctx, rw, sqe, iter);
+		*iovec = NULL;
+		return ret;
+	}
+
 #ifdef CONFIG_COMPAT
 	if (ctx->compat)
 		return compat_import_iovec(rw, buf, sqe->len, UIO_FASTIOV,
@@ -870,9 +924,19 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 		ret = io_nop(req, sqe);
 		break;
 	case IORING_OP_READV:
+		if (unlikely(sqe->buf_index))
+			return -EINVAL;
 		ret = io_read(req, sqe, force_nonblock, state);
 		break;
 	case IORING_OP_WRITEV:
+		if (unlikely(sqe->buf_index))
+			return -EINVAL;
+		ret = io_write(req, sqe, force_nonblock, state);
+		break;
+	case IORING_OP_READ_FIXED:
+		ret = io_read(req, sqe, force_nonblock, state);
+		break;
+	case IORING_OP_WRITE_FIXED:
 		ret = io_write(req, sqe, force_nonblock, state);
 		break;
 	case IORING_OP_FSYNC:
@@ -898,9 +962,11 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 static void io_sq_wq_submit_work(struct work_struct *work)
 {
 	struct io_kiocb *req = container_of(work, struct io_kiocb, work.work);
+	struct sqe_submit *s = &req->work.submit;
 	struct io_ring_ctx *ctx = req->ctx;
-	mm_segment_t old_fs = get_fs();
 	struct files_struct *old_files;
+	mm_segment_t old_fs;
+	bool needs_user;
 	int ret;
 
 	/*
@@ -913,19 +979,32 @@ static void io_sq_wq_submit_work(struct work_struct *work)
 	old_files = current->files;
 	current->files = ctx->sqo_files;
 
-	if (!mmget_not_zero(ctx->sqo_mm)) {
-		ret = -EFAULT;
-		goto err;
+	/*
+	 * If we're doing IO to fixed buffers, we don't need to get/set
+	 * user context
+	 */
+	needs_user = true;
+	if (s->sqe->opcode == IORING_OP_READ_FIXED ||
+	    s->sqe->opcode == IORING_OP_WRITE_FIXED)
+		needs_user = false;
+
+	if (needs_user) {
+		if (!mmget_not_zero(ctx->sqo_mm)) {
+			ret = -EFAULT;
+			goto err;
+		}
+		use_mm(ctx->sqo_mm);
+		old_fs = get_fs();
+		set_fs(USER_DS);
 	}
 
-	use_mm(ctx->sqo_mm);
-	set_fs(USER_DS);
-
 	ret = __io_submit_sqe(ctx, req, &req->work.submit, false, NULL);
 
-	set_fs(old_fs);
-	unuse_mm(ctx->sqo_mm);
-	mmput(ctx->sqo_mm);
+	if (needs_user) {
+		set_fs(old_fs);
+		unuse_mm(ctx->sqo_mm);
+		mmput(ctx->sqo_mm);
+	}
 err:
 	if (ret) {
 		io_fill_cq_error(ctx, &req->work.submit, ret);
@@ -1168,6 +1247,183 @@ static void io_sq_offload_stop(struct io_ring_ctx *ctx)
 	}
 }
 
+static int io_sqe_user_account_mem(struct io_ring_ctx *ctx,
+				   unsigned long nr_pages)
+{
+	unsigned long page_limit, cur_pages, new_pages;
+
+	if (!ctx->user)
+		return 0;
+
+	/* Don't allow more pages than we can safely lock */
+	page_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+
+	do {
+		cur_pages = atomic_long_read(&ctx->user->locked_vm);
+		new_pages = cur_pages + nr_pages;
+		if (new_pages > page_limit)
+			return -ENOMEM;
+	} while (atomic_long_cmpxchg(&ctx->user->locked_vm, cur_pages,
+					new_pages) != cur_pages);
+
+	return 0;
+}
+
+static int io_sqe_buffer_unregister(struct io_ring_ctx *ctx)
+{
+	int i, j;
+
+	if (!ctx->user_bufs)
+		return -EINVAL;
+
+	for (i = 0; i < ctx->sq_entries; i++) {
+		struct io_mapped_ubuf *imu = &ctx->user_bufs[i];
+
+		for (j = 0; j < imu->nr_bvecs; j++) {
+			set_page_dirty_lock(imu->bvec[j].bv_page);
+			put_page(imu->bvec[j].bv_page);
+		}
+
+		if (ctx->user)
+			atomic_long_sub(imu->nr_bvecs, &ctx->user->locked_vm);
+		kfree(imu->bvec);
+		imu->nr_bvecs = 0;
+	}
+
+	kfree(ctx->user_bufs);
+	ctx->user_bufs = NULL;
+	free_uid(ctx->user);
+	ctx->user = NULL;
+	return 0;
+}
+
+static int io_copy_iov(struct io_ring_ctx *ctx, struct iovec *dst,
+		       struct io_uring_register_buffers *reg, unsigned index)
+{
+	struct iovec __user *src;
+
+#ifdef CONFIG_COMPAT
+	if (ctx->compat) {
+		struct compat_iovec __user *ciovs;
+		struct compat_iovec ciov;
+
+		ciovs = (struct compat_iovec __user *) reg->iovecs;
+		if (copy_from_user(&ciov, &ciovs[index], sizeof(ciov)))
+			return -EFAULT;
+
+		dst->iov_base = (void __user *) (unsigned long) ciov.iov_base;
+		dst->iov_len = ciov.iov_len;
+		return 0;
+	}
+#endif
+	src = (struct iovec __user *) &reg->iovecs[index];
+	if (copy_from_user(dst, src, sizeof(*dst)))
+		return -EFAULT;
+	return 0;
+}
+
+static int io_sqe_buffer_register(struct io_ring_ctx *ctx,
+				  struct io_uring_register_buffers *reg)
+{
+	struct page **pages = NULL;
+	int i, j, got_pages = 0;
+	int ret = -EINVAL;
+
+	if (reg->nr_iovecs > USHRT_MAX)
+		return -EINVAL;
+
+	ctx->user_bufs = kcalloc(reg->nr_iovecs, sizeof(struct io_mapped_ubuf),
+					GFP_KERNEL);
+	if (!ctx->user_bufs)
+		return -ENOMEM;
+
+	if (!capable(CAP_IPC_LOCK))
+		ctx->user = get_uid(current_user());
+
+	for (i = 0; i < reg->nr_iovecs; i++) {
+		struct io_mapped_ubuf *imu = &ctx->user_bufs[i];
+		unsigned long off, start, end, ubuf;
+		int pret, nr_pages;
+		struct iovec iov;
+		size_t size;
+
+		ret = io_copy_iov(ctx, &iov, reg, i);
+		if (ret)
+			break;
+
+		/*
+		 * Don't impose further limits on the size and buffer
+		 * constraints here, we'll -EINVAL later when IO is
+		 * submitted if they are wrong.
+		 */
+		ret = -EFAULT;
+		if (!iov.iov_base)
+			goto err;
+
+		/* arbitrary limit, but we need something */
+		if (iov.iov_len > SZ_1G)
+			goto err;
+
+		ubuf = (unsigned long) iov.iov_base;
+		end = (ubuf + iov.iov_len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+		start = ubuf >> PAGE_SHIFT;
+		nr_pages = end - start;
+
+		ret = io_sqe_user_account_mem(ctx, nr_pages);
+		if (ret)
+			goto err;
+
+		if (!pages || nr_pages > got_pages) {
+			kfree(pages);
+			pages = kmalloc_array(nr_pages, sizeof(struct page *),
+						GFP_KERNEL);
+			if (!pages)
+				goto err;
+			got_pages = nr_pages;
+		}
+
+		imu->bvec = kmalloc_array(nr_pages, sizeof(struct bio_vec),
+						GFP_KERNEL);
+		if (!imu->bvec)
+			goto err;
+
+		down_write(&current->mm->mmap_sem);
+		pret = get_user_pages_longterm(ubuf, nr_pages, FOLL_WRITE,
+						pages, NULL);
+		up_write(&current->mm->mmap_sem);
+
+		if (pret < nr_pages) {
+			if (pret < 0)
+				ret = pret;
+			goto err;
+		}
+
+		off = ubuf & ~PAGE_MASK;
+		size = iov.iov_len;
+		for (j = 0; j < nr_pages; j++) {
+			size_t vec_len;
+
+			vec_len = min_t(size_t, size, PAGE_SIZE - off);
+			imu->bvec[j].bv_page = pages[j];
+			imu->bvec[j].bv_len = vec_len;
+			imu->bvec[j].bv_offset = off;
+			off = 0;
+			size -= vec_len;
+		}
+		/* store original address for later verification */
+		imu->ubuf = ubuf;
+		imu->len = iov.iov_len;
+		imu->nr_bvecs = nr_pages;
+	}
+	kfree(pages);
+	ctx->nr_user_bufs = reg->nr_iovecs;
+	return 0;
+err:
+	kfree(pages);
+	io_sqe_buffer_unregister(ctx);
+	return ret;
+}
+
 static void io_free_scq_urings(struct io_ring_ctx *ctx)
 {
 	if (ctx->sq_ring) {
@@ -1189,6 +1445,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
 	io_sq_offload_stop(ctx);
 	io_iopoll_reap_events(ctx);
 	io_free_scq_urings(ctx);
+	io_sqe_buffer_unregister(ctx);
 	percpu_ref_exit(&ctx->refs);
 	kfree(ctx);
 }
@@ -1436,6 +1693,74 @@ COMPAT_SYSCALL_DEFINE2(io_uring_setup, u32, entries,
 }
 #endif
 
+static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
+			       void __user *arg)
+{
+	int ret;
+
+	/* Drop our initial ref and wait for the ctx to be fully idle */
+	percpu_ref_put(&ctx->refs);
+	percpu_ref_kill(&ctx->refs);
+	wait_for_completion(&ctx->ctx_done);
+
+	switch (opcode) {
+	case IORING_REGISTER_BUFFERS: {
+		struct io_uring_register_buffers reg;
+
+		ret = -EFAULT;
+		if (copy_from_user(&reg, arg, sizeof(reg)))
+			break;
+		ret = io_sqe_buffer_register(ctx, &reg);
+		break;
+		}
+	case IORING_UNREGISTER_BUFFERS:
+		ret = -EINVAL;
+		if (arg)
+			break;
+		ret = io_sqe_buffer_unregister(ctx);
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+
+	/* bring the ctx back to life */
+	percpu_ref_resurrect(&ctx->refs);
+	percpu_ref_get(&ctx->refs);
+	return ret;
+}
+
+SYSCALL_DEFINE3(io_uring_register, unsigned int, fd, unsigned int, opcode,
+		void __user *, arg)
+{
+	struct io_ring_ctx *ctx;
+	long ret = -EBADF;
+	struct fd f;
+
+	f = fdget(fd);
+	if (!f.file)
+		return -EBADF;
+
+	ret = -EOPNOTSUPP;
+	if (f.file->f_op != &io_uring_fops)
+		goto out_fput;
+
+	ret = -EINVAL;
+	ctx = f.file->private_data;
+	if (!percpu_ref_tryget(&ctx->refs))
+		goto out_fput;
+
+	ret = -EBUSY;
+	if (mutex_trylock(&ctx->uring_lock)) {
+		ret = __io_uring_register(ctx, opcode, arg);
+		mutex_unlock(&ctx->uring_lock);
+	}
+	io_ring_drop_ctx_refs(ctx, 1);
+out_fput:
+	fdput(f);
+	return ret;
+}
+
 static int __init io_uring_init(void)
 {
 	req_cachep = KMEM_CACHE(io_kiocb, SLAB_HWCACHE_ALIGN | SLAB_PANIC);
diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index 39ad98c09c58..c7b5f86b91a1 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -40,7 +40,7 @@ struct user_struct {
 	kuid_t uid;
 
 #if defined(CONFIG_PERF_EVENTS) || defined(CONFIG_BPF_SYSCALL) || \
-    defined(CONFIG_NET)
+    defined(CONFIG_NET) || defined(CONFIG_IO_URING)
 	atomic_long_t locked_vm;
 #endif
 
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 542757a4c898..e36c264d74e8 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -314,6 +314,8 @@ asmlinkage long sys_io_uring_setup(u32 entries,
 				struct io_uring_params __user *p);
 asmlinkage long sys_io_uring_enter(unsigned int fd, u32 to_submit,
 				u32 min_complete, u32 flags);
+asmlinkage long sys_io_uring_register(unsigned int fd, unsigned op,
+				void __user *arg);
 
 /* fs/xattr.c */
 asmlinkage long sys_setxattr(const char __user *path, const char __user *name,
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index d31ae2f767d1..fda25d09c8a1 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -30,7 +30,10 @@ struct io_uring_sqe {
 		__u32		fsync_flags;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
-	__u64	__pad2[3];
+	union {
+		__u16	buf_index;	/* index into fixed buffers, if used */
+		__u64	__pad2[3];
+	};
 };
 
 /*
@@ -42,6 +45,8 @@ struct io_uring_sqe {
 #define IORING_OP_READV		1
 #define IORING_OP_WRITEV	2
 #define IORING_OP_FSYNC		3
+#define IORING_OP_READ_FIXED	4
+#define IORING_OP_WRITE_FIXED	5
 
 /*
  * sqe->fsync_flags
@@ -105,4 +110,18 @@ struct io_uring_params {
 	struct io_cqring_offsets cq_off;
 };
 
+/*
+ * io_uring_register(2) opcodes and arguments
+ */
+#define IORING_REGISTER_BUFFERS		0
+#define IORING_UNREGISTER_BUFFERS	1
+
+struct io_uring_register_buffers {
+	union {
+		struct iovec *iovecs;
+		__u64 pad;
+	};
+	__u32 nr_iovecs;
+};
+
 #endif
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index ee5e523564bb..1bb6604dc19f 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -48,6 +48,7 @@ COND_SYSCALL_COMPAT(io_getevents);
 COND_SYSCALL_COMPAT(io_pgetevents);
 COND_SYSCALL(io_uring_setup);
 COND_SYSCALL(io_uring_enter);
+COND_SYSCALL(io_uring_register);
 
 /* fs/xattr.c */
 
-- 
2.17.1

[PATCH 14/16] io_uring: add submission polling

[Jens Axboe]

This enables an application to do IO, without ever entering the kernel.
By using the SQ ring to fill in new sqes and watching for completions
on the CQ ring, we can submit and reap IOs without doing a single system
call. The kernel side thread will poll for new submissions, and in case
of HIPRI/polled IO, it'll also poll for completions.

Proof of concept. If the thread has been idle for 1 second, it will set
sq_ring->flags |= IORING_SQ_NEED_WAKEUP. The application will have to
call io_uring_enter() to start things back up again. If IO is kept busy,
that will never be needed. Basically an application that has this
feature enabled will guard it's io_uring_enter(2) call with:

read_barrier();
if (*sq_ring->flags & IORING_SQ_NEED_WAKEUP)
	io_uring_enter(fd, to_submit, 0, 0);

instead of calling it unconditionally.

Improvements:

1) Maybe have smarter backoff. Busy loop for X time, then go to
   monitor/mwait, finally the schedule we have now after an idle
   second. Might not be worth the complexity.

2) Probably want the application to pass in the appropriate grace
   period, not hard code it at 1 second.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 215 +++++++++++++++++++++++++++++++++-
 include/uapi/linux/io_uring.h |  10 +-
 2 files changed, 218 insertions(+), 7 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 00743a5a6fac..6df5da8b5259 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -23,6 +23,7 @@
 #include <linux/percpu.h>
 #include <linux/slab.h>
 #include <linux/workqueue.h>
+#include <linux/kthread.h>
 #include <linux/blkdev.h>
 #include <linux/bvec.h>
 #include <linux/anon_inodes.h>
@@ -91,8 +92,10 @@ struct io_ring_ctx {
 
 	/* IO offload */
 	struct workqueue_struct	*sqo_wq;
+	struct task_struct	*sqo_thread;	/* if using sq thread polling */
 	struct mm_struct	*sqo_mm;
 	struct files_struct	*sqo_files;
+	wait_queue_head_t	sqo_wait;
 
 	/* if used, fixed mapped user buffers */
 	unsigned		nr_user_bufs;
@@ -1112,6 +1115,167 @@ static bool io_peek_sqring(struct io_ring_ctx *ctx, struct sqe_submit *s)
 	return false;
 }
 
+static int io_submit_sqes(struct io_ring_ctx *ctx, struct sqe_submit *sqes,
+			  unsigned int nr, bool mm_fault)
+{
+	struct io_submit_state state, *statep = NULL;
+	int ret, i, submitted = 0;
+
+	if (nr > IO_PLUG_THRESHOLD) {
+		io_submit_state_start(&state, ctx, nr);
+		statep = &state;
+	}
+
+	for (i = 0; i < nr; i++) {
+		if (unlikely(mm_fault))
+			ret = -EFAULT;
+		else
+			ret = io_submit_sqe(ctx, &sqes[i], statep);
+		if (!ret) {
+			submitted++;
+			continue;
+		}
+
+		io_fill_cq_error(ctx, &sqes[i], ret);
+	}
+
+	if (statep)
+		io_submit_state_end(&state);
+
+	return submitted;
+}
+
+static int io_sq_thread(void *data)
+{
+	struct sqe_submit sqes[IO_IOPOLL_BATCH];
+	struct io_ring_ctx *ctx = data;
+	struct mm_struct *cur_mm = NULL;
+	struct files_struct *old_files;
+	mm_segment_t old_fs;
+	DEFINE_WAIT(wait);
+	unsigned inflight;
+	unsigned long timeout;
+
+	old_files = current->files;
+	current->files = ctx->sqo_files;
+
+	old_fs = get_fs();
+	set_fs(USER_DS);
+
+	timeout = inflight = 0;
+	while (!kthread_should_stop()) {
+		bool all_fixed, mm_fault = false;
+		int i;
+
+		if (inflight) {
+			unsigned int nr_events = 0;
+
+			/*
+			 * Normal IO, just pretend everything completed.
+			 * We don't have to poll completions for that.
+			 */
+			if (ctx->flags & IORING_SETUP_IOPOLL) {
+				/*
+				 * App should not use IORING_ENTER_GETEVENTS
+				 * with thread polling, but if it does, then
+				 * ensure we are mutually exclusive.
+				 */
+				if (mutex_trylock(&ctx->uring_lock)) {
+					io_iopoll_check(ctx, &nr_events, 0);
+					mutex_unlock(&ctx->uring_lock);
+				}
+			} else {
+				nr_events = inflight;
+			}
+
+			inflight -= nr_events;
+			if (!inflight)
+				timeout = jiffies + HZ;
+		}
+
+		if (!io_peek_sqring(ctx, &sqes[0])) {
+			/*
+			 * We're polling, let us spin for a second without
+			 * work before going to sleep.
+			 */
+			if (inflight || !time_after(jiffies, timeout)) {
+				cpu_relax();
+				continue;
+			}
+
+			/*
+			 * Drop cur_mm before scheduling, we can't hold it for
+			 * long periods (or over schedule()). Do this before
+			 * adding ourselves to the waitqueue, as the unuse/drop
+			 * may sleep.
+			 */
+			if (cur_mm) {
+				unuse_mm(cur_mm);
+				mmput(cur_mm);
+				cur_mm = NULL;
+			}
+
+			prepare_to_wait(&ctx->sqo_wait, &wait,
+						TASK_INTERRUPTIBLE);
+
+			/* Tell userspace we may need a wakeup call */
+			ctx->sq_ring->flags |= IORING_SQ_NEED_WAKEUP;
+			smp_wmb();
+
+			if (!io_peek_sqring(ctx, &sqes[0])) {
+				if (kthread_should_park())
+					kthread_parkme();
+				if (kthread_should_stop()) {
+					finish_wait(&ctx->sqo_wait, &wait);
+					break;
+				}
+				if (signal_pending(current))
+					flush_signals(current);
+				schedule();
+				finish_wait(&ctx->sqo_wait, &wait);
+
+				ctx->sq_ring->flags &= ~IORING_SQ_NEED_WAKEUP;
+				smp_wmb();
+				continue;
+			}
+			finish_wait(&ctx->sqo_wait, &wait);
+
+			ctx->sq_ring->flags &= ~IORING_SQ_NEED_WAKEUP;
+			smp_wmb();
+		}
+
+		i = 0;
+		all_fixed = true;
+		do {
+			if (sqes[i].sqe->opcode != IORING_OP_READ_FIXED &&
+			    sqes[i].sqe->opcode != IORING_OP_WRITE_FIXED)
+				all_fixed = false;
+			if (i + 1 == ARRAY_SIZE(sqes))
+				break;
+			i++;
+			io_inc_sqring(ctx);
+		} while (io_peek_sqring(ctx, &sqes[i]));
+
+		/* Unless all new commands are FIXED regions, grab mm */
+		if (!all_fixed && !cur_mm) {
+			mm_fault = !mmget_not_zero(ctx->sqo_mm);
+			if (!mm_fault) {
+				use_mm(ctx->sqo_mm);
+				cur_mm = ctx->sqo_mm;
+			}
+		}
+
+		inflight += io_submit_sqes(ctx, sqes, i, mm_fault);
+	}
+	current->files = old_files;
+	set_fs(old_fs);
+	if (cur_mm) {
+		unuse_mm(cur_mm);
+		mmput(cur_mm);
+	}
+	return 0;
+}
+
 static int io_ring_submit(struct io_ring_ctx *ctx, unsigned int to_submit)
 {
 	struct io_submit_state state, *statep = NULL;
@@ -1183,9 +1347,14 @@ static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
 	int ret = 0;
 
 	if (to_submit) {
-		ret = io_ring_submit(ctx, to_submit);
-		if (ret < 0)
-			return ret;
+		if (ctx->flags & IORING_SETUP_SQPOLL) {
+			wake_up(&ctx->sqo_wait);
+			ret = to_submit;
+		} else {
+			ret = io_ring_submit(ctx, to_submit);
+			if (ret < 0)
+				return ret;
+		}
 	}
 	if (flags & IORING_ENTER_GETEVENTS) {
 		unsigned nr_events = 0;
@@ -1206,10 +1375,12 @@ static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
 	return ret;
 }
 
-static int io_sq_offload_start(struct io_ring_ctx *ctx)
+static int io_sq_offload_start(struct io_ring_ctx *ctx,
+			       struct io_uring_params *p)
 {
 	int ret;
 
+	init_waitqueue_head(&ctx->sqo_wait);
 	ctx->sqo_mm = current->mm;
 
 	/*
@@ -1223,6 +1394,27 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx)
 	if (!ctx->sqo_files)
 		goto err;
 
+	if (ctx->flags & IORING_SETUP_SQPOLL) {
+		if (p->flags & IORING_SETUP_SQ_AFF) {
+			ctx->sqo_thread = kthread_create_on_cpu(io_sq_thread,
+							ctx, p->sq_thread_cpu,
+							"io_uring-sq");
+		} else {
+			ctx->sqo_thread = kthread_create(io_sq_thread, ctx,
+							"io_uring-sq");
+		}
+		if (IS_ERR(ctx->sqo_thread)) {
+			ret = PTR_ERR(ctx->sqo_thread);
+			ctx->sqo_thread = NULL;
+			goto err;
+		}
+		wake_up_process(ctx->sqo_thread);
+	} else if (p->flags & IORING_SETUP_SQ_AFF) {
+		/* Can't have SQ_AFF without SQPOLL */
+		ret = -EINVAL;
+		goto err;
+	}
+
 	/* Do QD, or 2 * CPUS, whatever is smallest */
 	ctx->sqo_wq = alloc_workqueue("io_ring-wq", WQ_UNBOUND | WQ_FREEZABLE,
 			min(ctx->sq_entries - 1, 2 * num_online_cpus()));
@@ -1233,6 +1425,11 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx)
 
 	return 0;
 err:
+	if (ctx->sqo_thread) {
+		kthread_park(ctx->sqo_thread);
+		kthread_stop(ctx->sqo_thread);
+		ctx->sqo_thread = NULL;
+	}
 	if (ctx->sqo_files)
 		ctx->sqo_files = NULL;
 	ctx->sqo_mm = NULL;
@@ -1241,6 +1438,11 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx)
 
 static void io_sq_offload_stop(struct io_ring_ctx *ctx)
 {
+	if (ctx->sqo_thread) {
+		kthread_park(ctx->sqo_thread);
+		kthread_stop(ctx->sqo_thread);
+		ctx->sqo_thread = NULL;
+	}
 	if (ctx->sqo_wq) {
 		destroy_workqueue(ctx->sqo_wq);
 		ctx->sqo_wq = NULL;
@@ -1631,7 +1833,7 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p,
 	if (ret)
 		goto err;
 
-	ret = io_sq_offload_start(ctx);
+	ret = io_sq_offload_start(ctx, p);
 	if (ret)
 		goto err;
 
@@ -1666,7 +1868,8 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params,
 			return -EINVAL;
 	}
 
-	if (p.flags & ~IORING_SETUP_IOPOLL)
+	if (p.flags & ~(IORING_SETUP_IOPOLL | IORING_SETUP_SQPOLL |
+			IORING_SETUP_SQ_AFF))
 		return -EINVAL;
 
 	ret = io_uring_create(entries, &p, compat);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index fda25d09c8a1..cb075971d8fb 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -40,6 +40,8 @@ struct io_uring_sqe {
  * io_uring_setup() flags
  */
 #define IORING_SETUP_IOPOLL	(1 << 0)	/* io_context is polled */
+#define IORING_SETUP_SQPOLL	(1 << 1)	/* SQ poll thread */
+#define IORING_SETUP_SQ_AFF	(1 << 2)	/* sq_thread_cpu is valid */
 
 #define IORING_OP_NOP		0
 #define IORING_OP_READV		1
@@ -83,6 +85,11 @@ struct io_sqring_offsets {
 	__u32 resv[3];
 };
 
+/*
+ * sq_ring->flags
+ */
+#define IORING_SQ_NEED_WAKEUP	(1 << 0) /* needs io_uring_enter wakeup */
+
 struct io_cqring_offsets {
 	__u32 head;
 	__u32 tail;
@@ -105,7 +112,8 @@ struct io_uring_params {
 	__u32 sq_entries;
 	__u32 cq_entries;
 	__u32 flags;
-	__u16 resv[10];
+	__u16 sq_thread_cpu;
+	__u16 resv[9];
 	struct io_sqring_offsets sq_off;
 	struct io_cqring_offsets cq_off;
 };
-- 
2.17.1

[PATCH 15/16] io_uring: add file registration

[Jens Axboe]

We normally have to fget/fput for each IO we do on a file. Even with
the batching we do, this atomic inc/dec cost adds up.

This adds IORING_REGISTER_FILES, and IORING_UNREGISTER_FILES opcodes
for the io_uring_register(2) system call. Pass in an array of fds
that are in use by the application, and we'll fget these for the
duration of the io_uring context.

When used, the application must set IOSQE_FIXED_FILE in the sqe->flags
member. Then, instead of setting sqe->fd to the real fd, it sets sqe->fd
to the index in the array passed in to IORING_REGISTER_FILES.

Files are automatically unregistered when the io_uring context is
torn down. An application need only unregister if it wishes to
register a few set of fds.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 135 +++++++++++++++++++++++++++++-----
 include/uapi/linux/io_uring.h |  17 ++++-
 2 files changed, 131 insertions(+), 21 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6df5da8b5259..fd89fcecd8e2 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -97,6 +97,10 @@ struct io_ring_ctx {
 	struct files_struct	*sqo_files;
 	wait_queue_head_t	sqo_wait;
 
+	/* if used, fixed file set */
+	struct file		**user_files;
+	unsigned		nr_user_files;
+
 	/* if used, fixed mapped user buffers */
 	unsigned		nr_user_bufs;
 	struct io_mapped_ubuf	*user_bufs;
@@ -137,6 +141,7 @@ struct io_kiocb {
 #define REQ_F_FORCE_NONBLOCK	1	/* inline submission attempt */
 #define REQ_F_IOPOLL_COMPLETED	2	/* polled IO has completed */
 #define REQ_F_IOPOLL_EAGAIN	4	/* submission got EAGAIN */
+#define REQ_F_FIXED_FILE	8	/* ctx owns file */
 	u64			user_data;
 	u64			res;
 };
@@ -391,15 +396,17 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 		 * Batched puts of the same file, to avoid dirtying the
 		 * file usage count multiple times, if avoidable.
 		 */
-		if (!file) {
-			file = req->rw.ki_filp;
-			file_count = 1;
-		} else if (file == req->rw.ki_filp) {
-			file_count++;
-		} else {
-			fput_many(file, file_count);
-			file = req->rw.ki_filp;
-			file_count = 1;
+		if (!(req->flags & REQ_F_FIXED_FILE)) {
+			if (!file) {
+				file = req->rw.ki_filp;
+				file_count = 1;
+			} else if (file == req->rw.ki_filp) {
+				file_count++;
+			} else {
+				fput_many(file, file_count);
+				file = req->rw.ki_filp;
+				file_count = 1;
+			}
 		}
 
 		if (to_free == ARRAY_SIZE(reqs))
@@ -530,13 +537,19 @@ static void kiocb_end_write(struct kiocb *kiocb)
 	}
 }
 
+static void io_fput(struct io_kiocb *req)
+{
+	if (!(req->flags & REQ_F_FIXED_FILE))
+		fput(req->rw.ki_filp);
+}
+
 static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
 {
 	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
 
 	kiocb_end_write(kiocb);
 
-	fput(kiocb->ki_filp);
+	io_fput(req);
 	io_cqring_fill_event(req->ctx, req->user_data, res, 0);
 	io_free_req(req);
 }
@@ -646,7 +659,17 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	struct kiocb *kiocb = &req->rw;
 	int ret;
 
-	kiocb->ki_filp = io_file_get(state, sqe->fd);
+	if (unlikely(sqe->flags & ~IOSQE_FIXED_FILE))
+		return -EINVAL;
+
+	if (sqe->flags & IOSQE_FIXED_FILE) {
+		if (unlikely(!ctx->user_files || sqe->fd >= ctx->nr_user_files))
+			return -EBADF;
+		kiocb->ki_filp = ctx->user_files[sqe->fd];
+		req->flags |= REQ_F_FIXED_FILE;
+	} else {
+		kiocb->ki_filp = io_file_get(state, sqe->fd);
+	}
 	if (unlikely(!kiocb->ki_filp))
 		return -EBADF;
 	kiocb->ki_pos = sqe->off;
@@ -685,7 +708,8 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	}
 	return 0;
 out_fput:
-	io_file_put(state, kiocb->ki_filp);
+	if (!(sqe->flags & IOSQE_FIXED_FILE))
+		io_file_put(state, kiocb->ki_filp);
 	return ret;
 }
 
@@ -801,7 +825,7 @@ static ssize_t io_read(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	kfree(iovec);
 out_fput:
 	if (unlikely(ret))
-		fput(file);
+		io_fput(req);
 	return ret;
 }
 
@@ -855,7 +879,7 @@ static ssize_t io_write(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 	}
 out_fput:
 	if (unlikely(ret))
-		fput(file);
+		io_fput(req);
 	return ret;
 }
 
@@ -888,19 +912,30 @@ static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 
 	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
 		return -EINVAL;
+	if (unlikely(sqe->flags & ~IOSQE_FIXED_FILE))
+		return -EINVAL;
 	if (unlikely(sqe->addr))
 		return -EINVAL;
 	if (unlikely(sqe->fsync_flags & ~IORING_FSYNC_DATASYNC))
 		return -EINVAL;
 
-	file = fget(sqe->fd);
+	if (sqe->flags & IOSQE_FIXED_FILE) {
+		if (unlikely(!ctx->user_files || sqe->fd >= ctx->nr_user_files))
+			return -EBADF;
+		file = ctx->user_files[sqe->fd];
+	} else {
+		file = fget(sqe->fd);
+	}
+
 	if (unlikely(!file))
 		return -EBADF;
 
 	ret = vfs_fsync_range(file, sqe->off, end > 0 ? end : LLONG_MAX,
 			sqe->fsync_flags & IORING_FSYNC_DATASYNC);
 
-	fput(file);
+	if (!(sqe->flags & IOSQE_FIXED_FILE))
+		fput(file);
+
 	io_cqring_fill_event(ctx, sqe->user_data, ret, 0);
 	io_free_req(req);
 	return 0;
@@ -913,10 +948,6 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	const struct io_uring_sqe *sqe = s->sqe;
 	ssize_t ret;
 
-	/* enforce forwards compatibility on users */
-	if (unlikely(sqe->flags))
-		return -EINVAL;
-
 	if (unlikely(s->index >= ctx->sq_entries))
 		return -EINVAL;
 	req->user_data = sqe->user_data;
@@ -1375,6 +1406,54 @@ static int __io_uring_enter(struct io_ring_ctx *ctx, unsigned to_submit,
 	return ret;
 }
 
+static int io_sqe_files_unregister(struct io_ring_ctx *ctx)
+{
+	int i;
+
+	if (!ctx->user_files)
+		return -EINVAL;
+
+	for (i = 0; i < ctx->nr_user_files; i++)
+		fput(ctx->user_files[i]);
+
+	kfree(ctx->user_files);
+	ctx->user_files = NULL;
+	ctx->nr_user_files = 0;
+	return 0;
+}
+
+static int io_sqe_files_register(struct io_ring_ctx *ctx,
+				 struct io_uring_register_files *reg)
+{
+	int fd, i, ret = 0;
+
+	ctx->user_files = kcalloc(reg->nr_fds, sizeof(struct file *),
+					GFP_KERNEL);
+	if (!ctx->user_files)
+		return -ENOMEM;
+
+	for (i = 0; i < reg->nr_fds; i++) {
+		__s32 __user *src = (__s32 __user *) &reg->fds[i];
+
+		ret = -EFAULT;
+		if (copy_from_user(&fd, src, sizeof(fd)))
+			break;
+
+		ctx->user_files[i] = fget(fd);
+
+		ret = -EBADF;
+		if (!ctx->user_files[i])
+			break;
+		ctx->nr_user_files++;
+		ret = 0;
+	}
+
+	if (ret)
+		io_sqe_files_unregister(ctx);
+
+	return ret;
+}
+
 static int io_sq_offload_start(struct io_ring_ctx *ctx,
 			       struct io_uring_params *p)
 {
@@ -1647,6 +1726,7 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
 	io_sq_offload_stop(ctx);
 	io_iopoll_reap_events(ctx);
 	io_free_scq_urings(ctx);
+	io_sqe_files_unregister(ctx);
 	io_sqe_buffer_unregister(ctx);
 	percpu_ref_exit(&ctx->refs);
 	kfree(ctx);
@@ -1922,6 +2002,21 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode,
 			break;
 		ret = io_sqe_buffer_unregister(ctx);
 		break;
+	case IORING_REGISTER_FILES: {
+		struct io_uring_register_files reg;
+
+		ret = -EFAULT;
+		if (copy_from_user(&reg, arg, sizeof(reg)))
+			break;
+		ret = io_sqe_files_register(ctx, &reg);
+		break;
+		}
+	case IORING_UNREGISTER_FILES:
+		ret = -EINVAL;
+		if (arg)
+			break;
+		ret = io_sqe_files_unregister(ctx);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index cb075971d8fb..3f367be56a9e 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -16,7 +16,7 @@
  */
 struct io_uring_sqe {
 	__u8	opcode;		/* type of operation for this sqe */
-	__u8	flags;		/* as of now unused */
+	__u8	flags;		/* IOSQE_ flags */
 	__u16	ioprio;		/* ioprio for the request */
 	__s32	fd;		/* file descriptor to do IO on */
 	__u64	off;		/* offset into file */
@@ -36,6 +36,11 @@ struct io_uring_sqe {
 	};
 };
 
+/*
+ * sqe->flags
+ */
+#define IOSQE_FIXED_FILE	(1 << 0)	/* use fixed fileset */
+
 /*
  * io_uring_setup() flags
  */
@@ -123,6 +128,8 @@ struct io_uring_params {
  */
 #define IORING_REGISTER_BUFFERS		0
 #define IORING_UNREGISTER_BUFFERS	1
+#define IORING_REGISTER_FILES		2
+#define IORING_UNREGISTER_FILES		3
 
 struct io_uring_register_buffers {
 	union {
@@ -132,4 +139,12 @@ struct io_uring_register_buffers {
 	__u32 nr_iovecs;
 };
 
+struct io_uring_register_files {
+	union {
+		__s32 *fds;
+		__u64 pad;
+	};
+	__u32 nr_fds;
+};
+
 #endif
-- 
2.17.1

[PATCH 16/16] io_uring: add io_uring_event cache hit information

[Jens Axboe]

Add hint on whether a read was served out of the page cache, or if it
hit media. This is useful for buffered async IO, O_DIRECT reads would
never have this set (for obvious reasons).

If the read hit page cache, cqe->flags will have IOCQE_FLAG_CACHEHIT
set.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c                 | 7 ++++++-
 include/uapi/linux/io_uring.h | 5 +++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index fd89fcecd8e2..4a74a40cd134 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -546,11 +546,16 @@ static void io_fput(struct io_kiocb *req)
 static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
 {
 	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
+	unsigned ev_flags = 0;
 
 	kiocb_end_write(kiocb);
 
 	io_fput(req);
-	io_cqring_fill_event(req->ctx, req->user_data, res, 0);
+
+	if (res > 0 && (req->flags & REQ_F_FORCE_NONBLOCK))
+		ev_flags = IOCQE_FLAG_CACHEHIT;
+
+	io_cqring_fill_event(req->ctx, req->user_data, res, ev_flags);
 	io_free_req(req);
 }
 
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 3f367be56a9e..71e92026d26c 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -69,6 +69,11 @@ struct io_uring_cqe {
 	__u32	flags;
 };
 
+/*
+ * io_uring_event->flags
+ */
+#define IOCQE_FLAG_CACHEHIT	(1 << 0)	/* IO did not hit media */
+
 /*
  * Magic offsets for the application to mmap the data it needs
  */
-- 
2.17.1

Re: [PATCH 05/16] Add io_uring IO interface

[Jonathan Corbet]

On Mon, 14 Jan 2019 19:55:20 -0700
Jens Axboe <axboe@kernel.dk> wrote:

So the [0/16] cover letter seems to have gone astray this time?

Anyway, a couple of minor notes/questions:

> The submission queue (SQ) and completion queue (CQ) rings are shared
> between the application and the kernel. This eliminates the need to
> copy data back and forth to submit and complete IO.
> 
> IO submissions use the io_uring_sqe data structure, and completions
> are generated in the form of io_uring_sqe data structures. The SQ
> ring is an index into the io_uring_sqe array, which makes it possible
> to submit a batch of IOs without them being contiguous in the ring.
> The CQ ring is always contiguous, as completion events are inherently
> unordered and can point to any io_uring_iocb.
> 
> Two new system calls are added for this:
> 
> io_uring_setup(entries, iovecs, params)
> 	Sets up a context for doing async IO. On success, returns a file
> 	descriptor that the application can mmap to gain access to the
> 	SQ ring, CQ ring, and io_uring_iocbs.

Looking at the code, it would appear that the "iovecs" parameter doesn't
actually exist.

> io_uring_enter(fd, to_submit, min_complete, flags)
> 	Initiates IO against the rings mapped to this fd, or waits for
> 	them to complete, or both The behavior is controlled by the
> 	parameters passed in. If 'min_complete' is non-zero, then we'll
> 	try and submit new IO. If IORING_ENTER_GETEVENTS is set, the
> 	kernel will wait for 'min_complete' events, if they aren't
> 	already available.

I feel like I'm missing something here.  Rather than have the
IORING_ENTER_GETEVENTS flag, why not just wait if min_complete > 0 ?

Thanks,

jon

Re: [PATCH 05/16] Add io_uring IO interface

[Jens Axboe]

On 1/15/19 9:51 AM, Jonathan Corbet wrote:
> On Mon, 14 Jan 2019 19:55:20 -0700
> Jens Axboe <axboe@kernel.dk> wrote:
> 
> So the [0/16] cover letter seems to have gone astray this time?

It did go out, but I forgot to add a Subject line to it...

https://marc.info/?l=linux-block&m=154752095709422&w=2


>> The submission queue (SQ) and completion queue (CQ) rings are shared
>> between the application and the kernel. This eliminates the need to
>> copy data back and forth to submit and complete IO.
>>
>> IO submissions use the io_uring_sqe data structure, and completions
>> are generated in the form of io_uring_sqe data structures. The SQ
>> ring is an index into the io_uring_sqe array, which makes it possible
>> to submit a batch of IOs without them being contiguous in the ring.
>> The CQ ring is always contiguous, as completion events are inherently
>> unordered and can point to any io_uring_iocb.
>>
>> Two new system calls are added for this:
>>
>> io_uring_setup(entries, iovecs, params)
>> 	Sets up a context for doing async IO. On success, returns a file
>> 	descriptor that the application can mmap to gain access to the
>> 	SQ ring, CQ ring, and io_uring_iocbs.
> 
> Looking at the code, it would appear that the "iovecs" parameter doesn't
> actually exist.

Indeed, need to update that commit message. and io_uring_iocbs should
now be io_uring_sqes.

The iovec/file registration is done through io_uring_register(2).

>> io_uring_enter(fd, to_submit, min_complete, flags)
>> 	Initiates IO against the rings mapped to this fd, or waits for
>> 	them to complete, or both The behavior is controlled by the
>> 	parameters passed in. If 'min_complete' is non-zero, then we'll
>> 	try and submit new IO. If IORING_ENTER_GETEVENTS is set, the
>> 	kernel will wait for 'min_complete' events, if they aren't
>> 	already available.
> 
> I feel like I'm missing something here.  Rather than have the
> IORING_ENTER_GETEVENTS flag, why not just wait if min_complete > 0 ?

For polled IO, it's useful to be able to check if we have events that
can be readily reaped. If min_complete > 0, then you're asking the
interface to wait/poll for these events. IORING_ENTER_GETEVENTS +
min_complete == 0 is a valid combination to just reap events that are
already completed.

-- 
Jens Axboe

Re: [PATCH 05/16] Add io_uring IO interface

[Jens Axboe]

On 1/15/19 9:55 AM, Jens Axboe wrote:
> On 1/15/19 9:51 AM, Jonathan Corbet wrote:
>> On Mon, 14 Jan 2019 19:55:20 -0700
>> Jens Axboe <axboe@kernel.dk> wrote:
>>
>> So the [0/16] cover letter seems to have gone astray this time?
> 
> It did go out, but I forgot to add a Subject line to it...
> 
> https://marc.info/?l=linux-block&m=154752095709422&w=2
> 
> 
>>> The submission queue (SQ) and completion queue (CQ) rings are shared
>>> between the application and the kernel. This eliminates the need to
>>> copy data back and forth to submit and complete IO.
>>>
>>> IO submissions use the io_uring_sqe data structure, and completions
>>> are generated in the form of io_uring_sqe data structures. The SQ
>>> ring is an index into the io_uring_sqe array, which makes it possible
>>> to submit a batch of IOs without them being contiguous in the ring.
>>> The CQ ring is always contiguous, as completion events are inherently
>>> unordered and can point to any io_uring_iocb.
>>>
>>> Two new system calls are added for this:
>>>
>>> io_uring_setup(entries, iovecs, params)
>>> 	Sets up a context for doing async IO. On success, returns a file
>>> 	descriptor that the application can mmap to gain access to the
>>> 	SQ ring, CQ ring, and io_uring_iocbs.
>>
>> Looking at the code, it would appear that the "iovecs" parameter doesn't
>> actually exist.
> 
> Indeed, need to update that commit message. and io_uring_iocbs should
> now be io_uring_sqes.
> 
> The iovec/file registration is done through io_uring_register(2).

Updated commit message which covers both this one, and the
IORING_ENTER_GETEVENTS below.

http://git.kernel.dk/cgit/linux-block/commit/?h=io_uring&id=d14a06629baef2b0701dbd01ac9c9066f73065ec

-- 
Jens Axboe

Re: [PATCH 05/16] Add io_uring IO interface

[Arnd Bergmann]

On Tue, Jan 15, 2019 at 3:55 AM Jens Axboe <axboe@kernel.dk> wrote:
>
> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> index 3cf7b533b3d1..194e79c0032e 100644
> --- a/arch/x86/entry/syscalls/syscall_32.tbl
> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> @@ -398,3 +398,5 @@
>  384    i386    arch_prctl              sys_arch_prctl                  __ia32_compat_sys_arch_prctl
>  385    i386    io_pgetevents           sys_io_pgetevents               __ia32_compat_sys_io_pgetevents
>  386    i386    rseq                    sys_rseq                        __ia32_sys_rseq
> +387    i386    io_uring_setup          sys_io_uring_setup              __ia32_compat_sys_io_uring_setup
> +388    i386    io_uring_enter          sys_io_uring_enter              __ia32_sys_io_uring_enter
> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> index f0b1709a5ffb..453ff7a79002 100644
> --- a/arch/x86/entry/syscalls/syscall_64.tbl
> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> @@ -343,6 +343,8 @@
>  332    common  statx                   __x64_sys_statx
>  333    common  io_pgetevents           __x64_sys_io_pgetevents
>  334    common  rseq                    __x64_sys_rseq
> +335    common  io_uring_setup          __x64_sys_io_uring_setup
> +336    common  io_uring_enter          __x64_sys_io_uring_enter

In my series for the y2038 system calls, I'm trying to move to having the
same numbers across all architectures. Unfortunately, that clashes
with newly assigned numbers here, so one of us needs to pick new
numbers.

If my series gets merged without other changes to the numbers, the next
available numbers on all architectures become 424 and 425.

Could you use those here?

> +SYSCALL_DEFINE2(io_uring_setup, u32, entries,
> +               struct io_uring_params __user *, params)
> +{
> +       return io_uring_setup(entries, params, false);
> +}
> +
> +#ifdef CONFIG_COMPAT
> +COMPAT_SYSCALL_DEFINE2(io_uring_setup, u32, entries,
> +                      struct io_uring_params __user *, params)
> +{
> +       return io_uring_setup(entries, params, true);
> +}
> +#endif

The compat syscall has the same calling conventions as the
native one here, so I think you can just use that directly.

> +/*
> + * IO submission data structure (Submission Queue Entry)
> + */
> +struct io_uring_sqe {
> +       __u8    opcode;         /* type of operation for this sqe */
> +       __u8    flags;          /* as of now unused */
> +       __u16   ioprio;         /* ioprio for the request */
> +       __s32   fd;             /* file descriptor to do IO on */
> +       __u64   off;            /* offset into file */
> +       union {
> +               void    *addr;  /* buffer or iovecs */
> +               __u64   __pad;
> +       };

It seems a bit unfortunate to keep the pointer field only
almost compatible between 32-bit and 64-bit big-endian
architectures, as that requires an in_compat_syscall()
check whenever we access the pointer from the kernel.

Could you use a __u64 field to store the pointer itself
instead?

> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index ab9d0e3c6d50..ee5e523564bb 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -46,6 +46,8 @@ COND_SYSCALL(io_getevents);
>  COND_SYSCALL(io_pgetevents);
>  COND_SYSCALL_COMPAT(io_getevents);
>  COND_SYSCALL_COMPAT(io_pgetevents);
> +COND_SYSCALL(io_uring_setup);
> +COND_SYSCALL(io_uring_enter);

Unless you remove the compat_sys_io_uring_setup() definition,
this should also have a corresponding COND_SYSCALL_COMPAT()
entry.

      Arnd

Re: [PATCH 15/16] io_uring: add file registration

[Arnd Bergmann]

On Tue, Jan 15, 2019 at 3:56 AM Jens Axboe <axboe@kernel.dk> wrote:

> @@ -132,4 +139,12 @@ struct io_uring_register_buffers {
>         __u32 nr_iovecs;
>  };
>
> +struct io_uring_register_files {
> +       union {
> +               __s32 *fds;
> +               __u64 pad;
> +       };
> +       __u32 nr_fds;
> +};

I think you should either remove the pad field here, or pass the pointer
using a __u64 argument itself. With the current definition, the ioctl
command code is the same between 32-bit and 64-bit architectures
(since the length is the same on anything other than x86), but the
structures are incompatible.

I would also suggest adding an explicit 32-bit pad field at the end
of the structure, to avoid the implicit padding on non-i386 machines.

     Arnd

Re: [PATCH 13/16] io_uring: add support for pre-mapped user IO buffers

[Arnd Bergmann]

On Tue, Jan 15, 2019 at 3:56 AM Jens Axboe <axboe@kernel.dk> wrote:

> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 542757a4c898..e36c264d74e8 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -314,6 +314,8 @@ asmlinkage long sys_io_uring_setup(u32 entries,
>                                 struct io_uring_params __user *p);
>  asmlinkage long sys_io_uring_enter(unsigned int fd, u32 to_submit,
>                                 u32 min_complete, u32 flags);
> +asmlinkage long sys_io_uring_register(unsigned int fd, unsigned op,
> +                               void __user *arg);
>

Would it be possible to make this a typed pointer instead? If this needs to
be extended later to pass a different structure, a new system call may
be better for consistency than overloading the argument in various
ways.

> + * io_uring_register(2) opcodes and arguments
> + */
> +#define IORING_REGISTER_BUFFERS                0
> +#define IORING_UNREGISTER_BUFFERS      1
> +
> +struct io_uring_register_buffers {
> +       union {
> +               struct iovec *iovecs;
> +               __u64 pad;
> +       };
> +       __u32 nr_iovecs;
> +};

As before, I'd suggest making this structure compatible between 32-bit
and 64-bit architectectures, by avoiding pointer and implied padding
fields.

      Arnd

Re: [PATCH 05/16] Add io_uring IO interface

[Arnd Bergmann]

On Wed, Jan 16, 2019 at 11:41 AM Arnd Bergmann <arnd@arndb.de> wrote:
> > +/*
> > + * IO submission data structure (Submission Queue Entry)
> > + */
> > +struct io_uring_sqe {
> > +       __u8    opcode;         /* type of operation for this sqe */
> > +       __u8    flags;          /* as of now unused */
> > +       __u16   ioprio;         /* ioprio for the request */
> > +       __s32   fd;             /* file descriptor to do IO on */
> > +       __u64   off;            /* offset into file */
> > +       union {
> > +               void    *addr;  /* buffer or iovecs */
> > +               __u64   __pad;
> > +       };
>
> It seems a bit unfortunate to keep the pointer field only
> almost compatible between 32-bit and 64-bit big-endian
> architectures, as that requires an in_compat_syscall()
> check whenever we access the pointer from the kernel.
>
> Could you use a __u64 field to store the pointer itself
> instead?

To clarify: Using the u64_to_user_ptr() helper function,
you can interpret a __u64 field in a uapi data structure
directly as a pointer. The user space side needs a similar
wrapper though.

     Arnd

Re: [PATCH 05/16] Add io_uring IO interface

[Jens Axboe]

On 1/16/19 3:41 AM, Arnd Bergmann wrote:
> On Tue, Jan 15, 2019 at 3:55 AM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
>> index 3cf7b533b3d1..194e79c0032e 100644
>> --- a/arch/x86/entry/syscalls/syscall_32.tbl
>> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
>> @@ -398,3 +398,5 @@
>>  384    i386    arch_prctl              sys_arch_prctl                  __ia32_compat_sys_arch_prctl
>>  385    i386    io_pgetevents           sys_io_pgetevents               __ia32_compat_sys_io_pgetevents
>>  386    i386    rseq                    sys_rseq                        __ia32_sys_rseq
>> +387    i386    io_uring_setup          sys_io_uring_setup              __ia32_compat_sys_io_uring_setup
>> +388    i386    io_uring_enter          sys_io_uring_enter              __ia32_sys_io_uring_enter
>> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
>> index f0b1709a5ffb..453ff7a79002 100644
>> --- a/arch/x86/entry/syscalls/syscall_64.tbl
>> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
>> @@ -343,6 +343,8 @@
>>  332    common  statx                   __x64_sys_statx
>>  333    common  io_pgetevents           __x64_sys_io_pgetevents
>>  334    common  rseq                    __x64_sys_rseq
>> +335    common  io_uring_setup          __x64_sys_io_uring_setup
>> +336    common  io_uring_enter          __x64_sys_io_uring_enter
> 
> In my series for the y2038 system calls, I'm trying to move to having the
> same numbers across all architectures. Unfortunately, that clashes
> with newly assigned numbers here, so one of us needs to pick new
> numbers.
> 
> If my series gets merged without other changes to the numbers, the next
> available numbers on all architectures become 424 and 425.
> 
> Could you use those here?

Yeah that's totally fine, I don't really care what the numbers end up
being, that side isn't fixed for me.

>> +SYSCALL_DEFINE2(io_uring_setup, u32, entries,
>> +               struct io_uring_params __user *, params)
>> +{
>> +       return io_uring_setup(entries, params, false);
>> +}
>> +
>> +#ifdef CONFIG_COMPAT
>> +COMPAT_SYSCALL_DEFINE2(io_uring_setup, u32, entries,
>> +                      struct io_uring_params __user *, params)
>> +{
>> +       return io_uring_setup(entries, params, true);
>> +}
>> +#endif
> 
> The compat syscall has the same calling conventions as the
> native one here, so I think you can just use that directly.

Not sure I understand what you mean here. I need to know if it's the
compat one, hence 'true' vs 'false', so I know what the size of the user
pointers/structs are.

>> +/*
>> + * IO submission data structure (Submission Queue Entry)
>> + */
>> +struct io_uring_sqe {
>> +       __u8    opcode;         /* type of operation for this sqe */
>> +       __u8    flags;          /* as of now unused */
>> +       __u16   ioprio;         /* ioprio for the request */
>> +       __s32   fd;             /* file descriptor to do IO on */
>> +       __u64   off;            /* offset into file */
>> +       union {
>> +               void    *addr;  /* buffer or iovecs */
>> +               __u64   __pad;
>> +       };
> 
> It seems a bit unfortunate to keep the pointer field only
> almost compatible between 32-bit and 64-bit big-endian
> architectures, as that requires an in_compat_syscall()
> check whenever we access the pointer from the kernel.
> 
> Could you use a __u64 field to store the pointer itself
> instead?

I feel like I'm missing something here, we'll still need the compat code
on the kernel side for 32-bit app on 64-bit kernel, so what would we
solve by making this an __u64?

>> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
>> index ab9d0e3c6d50..ee5e523564bb 100644
>> --- a/kernel/sys_ni.c
>> +++ b/kernel/sys_ni.c
>> @@ -46,6 +46,8 @@ COND_SYSCALL(io_getevents);
>>  COND_SYSCALL(io_pgetevents);
>>  COND_SYSCALL_COMPAT(io_getevents);
>>  COND_SYSCALL_COMPAT(io_pgetevents);
>> +COND_SYSCALL(io_uring_setup);
>> +COND_SYSCALL(io_uring_enter);
> 
> Unless you remove the compat_sys_io_uring_setup() definition,
> this should also have a corresponding COND_SYSCALL_COMPAT()
> entry.

Gotcha, thanks! I'll make that change.

-- 
Jens Axboe

Re: [PATCH 13/16] io_uring: add support for pre-mapped user IO buffers

[Jens Axboe]

On 1/16/19 3:53 AM, Arnd Bergmann wrote:
> On Tue, Jan 15, 2019 at 3:56 AM Jens Axboe <axboe@kernel.dk> wrote:
> 
>> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
>> index 542757a4c898..e36c264d74e8 100644
>> --- a/include/linux/syscalls.h
>> +++ b/include/linux/syscalls.h
>> @@ -314,6 +314,8 @@ asmlinkage long sys_io_uring_setup(u32 entries,
>>                                 struct io_uring_params __user *p);
>>  asmlinkage long sys_io_uring_enter(unsigned int fd, u32 to_submit,
>>                                 u32 min_complete, u32 flags);
>> +asmlinkage long sys_io_uring_register(unsigned int fd, unsigned op,
>> +                               void __user *arg);
>>
> 
> Would it be possible to make this a typed pointer instead? If this needs to
> be extended later to pass a different structure, a new system call may
> be better for consistency than overloading the argument in various
> ways.

As you can see from the later patch for registering files, it'll be used
for other structs too. Feels a little silly to add an extra system call
for that. I agree the void * isn't the prettiest thing in the world, but
at least it allows us to extend the API without having to add even more
system calls down the line.

>> + * io_uring_register(2) opcodes and arguments
>> + */
>> +#define IORING_REGISTER_BUFFERS                0
>> +#define IORING_UNREGISTER_BUFFERS      1
>> +
>> +struct io_uring_register_buffers {
>> +       union {
>> +               struct iovec *iovecs;
>> +               __u64 pad;
>> +       };
>> +       __u32 nr_iovecs;
>> +};
> 
> As before, I'd suggest making this structure compatible between 32-bit
> and 64-bit architectectures, by avoiding pointer and implied padding
> fields.

I'll await an answer to my previous question on that.

-- 
Jens Axboe

Re: [PATCH 15/16] io_uring: add file registration

[Jens Axboe]

On 1/16/19 3:45 AM, Arnd Bergmann wrote:
> On Tue, Jan 15, 2019 at 3:56 AM Jens Axboe <axboe@kernel.dk> wrote:
> 
>> @@ -132,4 +139,12 @@ struct io_uring_register_buffers {
>>         __u32 nr_iovecs;
>>  };
>>
>> +struct io_uring_register_files {
>> +       union {
>> +               __s32 *fds;
>> +               __u64 pad;
>> +       };
>> +       __u32 nr_fds;
>> +};
> 
> I think you should either remove the pad field here, or pass the pointer
> using a __u64 argument itself. With the current definition, the ioctl
> command code is the same between 32-bit and 64-bit architectures
> (since the length is the same on anything other than x86), but the
> structures are incompatible.

Ah ok, I think I'm starting to follow. Thanks Arnd, that's useful.
I'll make the changes throughout the structs.

> I would also suggest adding an explicit 32-bit pad field at the end
> of the structure, to avoid the implicit padding on non-i386 machines.

That's a good point, I'll make that change, that was an oversight.

-- 
Jens Axboe

Re: [PATCH 05/16] Add io_uring IO interface

[Arnd Bergmann]

On Wed, Jan 16, 2019 at 4:12 PM Jens Axboe <axboe@kernel.dk> wrote:
> On 1/16/19 3:41 AM, Arnd Bergmann wrote:
> > On Tue, Jan 15, 2019 at 3:55 AM Jens Axboe <axboe@kernel.dk> wrote:
> >> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> >> index 3cf7b533b3d1..194e79c0032e 100644
> >> --- a/arch/x86/entry/syscalls/syscall_32.tbl
> >> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> >> +SYSCALL_DEFINE2(io_uring_setup, u32, entries,
> >> +               struct io_uring_params __user *, params)
> >> +{
> >> +       return io_uring_setup(entries, params, false);
> >> +}
> >> +
> >> +#ifdef CONFIG_COMPAT
> >> +COMPAT_SYSCALL_DEFINE2(io_uring_setup, u32, entries,
> >> +                      struct io_uring_params __user *, params)
> >> +{
> >> +       return io_uring_setup(entries, params, true);
> >> +}
> >> +#endif
> >
> > The compat syscall has the same calling conventions as the
> > native one here, so I think you can just use that directly.
>
> Not sure I understand what you mean here. I need to know if it's the
> compat one, hence 'true' vs 'false', so I know what the size of the user
> pointers/structs are.

My mistake, I missed the true/false difference between the two
functions.

> >> +/*
> >> + * IO submission data structure (Submission Queue Entry)
> >> + */
> >> +struct io_uring_sqe {
> >> +       __u8    opcode;         /* type of operation for this sqe */
> >> +       __u8    flags;          /* as of now unused */
> >> +       __u16   ioprio;         /* ioprio for the request */
> >> +       __s32   fd;             /* file descriptor to do IO on */
> >> +       __u64   off;            /* offset into file */
> >> +       union {
> >> +               void    *addr;  /* buffer or iovecs */
> >> +               __u64   __pad;
> >> +       };
> >
> > It seems a bit unfortunate to keep the pointer field only
> > almost compatible between 32-bit and 64-bit big-endian
> > architectures, as that requires an in_compat_syscall()
> > check whenever we access the pointer from the kernel.
> >
> > Could you use a __u64 field to store the pointer itself
> > instead?
>
> I feel like I'm missing something here, we'll still need the compat code
> on the kernel side for 32-bit app on 64-bit kernel, so what would we
> solve by making this an __u64?

It means you don't have to define a compat_io_uring_sqe
structure with a compat_uptr_t member in it.

      Arnd

Re: [PATCH 05/16] Add io_uring IO interface

[Jens Axboe]

On 1/16/19 8:16 AM, Arnd Bergmann wrote:
> On Wed, Jan 16, 2019 at 4:12 PM Jens Axboe <axboe@kernel.dk> wrote:
>> On 1/16/19 3:41 AM, Arnd Bergmann wrote:
>>> On Tue, Jan 15, 2019 at 3:55 AM Jens Axboe <axboe@kernel.dk> wrote:
>>>> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
>>>> index 3cf7b533b3d1..194e79c0032e 100644
>>>> --- a/arch/x86/entry/syscalls/syscall_32.tbl
>>>> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
>>>> +SYSCALL_DEFINE2(io_uring_setup, u32, entries,
>>>> +               struct io_uring_params __user *, params)
>>>> +{
>>>> +       return io_uring_setup(entries, params, false);
>>>> +}
>>>> +
>>>> +#ifdef CONFIG_COMPAT
>>>> +COMPAT_SYSCALL_DEFINE2(io_uring_setup, u32, entries,
>>>> +                      struct io_uring_params __user *, params)
>>>> +{
>>>> +       return io_uring_setup(entries, params, true);
>>>> +}
>>>> +#endif
>>>
>>> The compat syscall has the same calling conventions as the
>>> native one here, so I think you can just use that directly.
>>
>> Not sure I understand what you mean here. I need to know if it's the
>> compat one, hence 'true' vs 'false', so I know what the size of the user
>> pointers/structs are.
> 
> My mistake, I missed the true/false difference between the two
> functions.
> 
>>>> +/*
>>>> + * IO submission data structure (Submission Queue Entry)
>>>> + */
>>>> +struct io_uring_sqe {
>>>> +       __u8    opcode;         /* type of operation for this sqe */
>>>> +       __u8    flags;          /* as of now unused */
>>>> +       __u16   ioprio;         /* ioprio for the request */
>>>> +       __s32   fd;             /* file descriptor to do IO on */
>>>> +       __u64   off;            /* offset into file */
>>>> +       union {
>>>> +               void    *addr;  /* buffer or iovecs */
>>>> +               __u64   __pad;
>>>> +       };
>>>
>>> It seems a bit unfortunate to keep the pointer field only
>>> almost compatible between 32-bit and 64-bit big-endian
>>> architectures, as that requires an in_compat_syscall()
>>> check whenever we access the pointer from the kernel.
>>>
>>> Could you use a __u64 field to store the pointer itself
>>> instead?
>>
>> I feel like I'm missing something here, we'll still need the compat code
>> on the kernel side for 32-bit app on 64-bit kernel, so what would we
>> solve by making this an __u64?
> 
> It means you don't have to define a compat_io_uring_sqe
> structure with a compat_uptr_t member in it.

Yeah, I finally got it, I'm making the change. Thanks!

-- 
Jens Axboe

Re: [PATCH 13/16] io_uring: add support for pre-mapped user IO buffers

[Jens Axboe]

On 1/16/19 8:14 AM, Jens Axboe wrote:
> On 1/16/19 3:53 AM, Arnd Bergmann wrote:
>> On Tue, Jan 15, 2019 at 3:56 AM Jens Axboe <axboe@kernel.dk> wrote:
>>
>>> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
>>> index 542757a4c898..e36c264d74e8 100644
>>> --- a/include/linux/syscalls.h
>>> +++ b/include/linux/syscalls.h
>>> @@ -314,6 +314,8 @@ asmlinkage long sys_io_uring_setup(u32 entries,
>>>                                 struct io_uring_params __user *p);
>>>  asmlinkage long sys_io_uring_enter(unsigned int fd, u32 to_submit,
>>>                                 u32 min_complete, u32 flags);
>>> +asmlinkage long sys_io_uring_register(unsigned int fd, unsigned op,
>>> +                               void __user *arg);
>>>
>>
>> Would it be possible to make this a typed pointer instead? If this needs to
>> be extended later to pass a different structure, a new system call may
>> be better for consistency than overloading the argument in various
>> ways.
> 
> As you can see from the later patch for registering files, it'll be used
> for other structs too. Feels a little silly to add an extra system call
> for that. I agree the void * isn't the prettiest thing in the world, but
> at least it allows us to extend the API without having to add even more
> system calls down the line.

With the __u64 changes, we end up with this:

struct io_uring_register_buffers {
	__u64 iovecs;		/* pointer to iovecs array */
	__u32 nr_iovecs;	/* number of iovecs in array */
	__u32 pad;
};

struct io_uring_register_files {
	__u64 fds;
	__u32 nr_fds;
	__u32 pad;
};

which are identical. So the question then becomes if I should just make
these opaque enough to be the same thing, ala:

struct io_uring_register_data {
	__u64 data;
	__u32 nr_elems;
	__u32 pad;
};

and then probably add a bit more reserved space so we have something
that can be extended...

-- 
Jens Axboe

Re: [PATCH 13/16] io_uring: add support for pre-mapped user IO buffers

[Arnd Bergmann]

On Wed, Jan 16, 2019 at 4:32 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 1/16/19 8:14 AM, Jens Axboe wrote:
> > On 1/16/19 3:53 AM, Arnd Bergmann wrote:
> >> On Tue, Jan 15, 2019 at 3:56 AM Jens Axboe <axboe@kernel.dk> wrote:
> >>
> >>> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> >>> index 542757a4c898..e36c264d74e8 100644
> >>> --- a/include/linux/syscalls.h
> >>> +++ b/include/linux/syscalls.h
> >>> @@ -314,6 +314,8 @@ asmlinkage long sys_io_uring_setup(u32 entries,
> >>>                                 struct io_uring_params __user *p);
> >>>  asmlinkage long sys_io_uring_enter(unsigned int fd, u32 to_submit,
> >>>                                 u32 min_complete, u32 flags);
> >>> +asmlinkage long sys_io_uring_register(unsigned int fd, unsigned op,
> >>> +                               void __user *arg);
> >>>
> >>
> >> Would it be possible to make this a typed pointer instead? If this needs to
> >> be extended later to pass a different structure, a new system call may
> >> be better for consistency than overloading the argument in various
> >> ways.
> >
> > As you can see from the later patch for registering files, it'll be used
> > for other structs too. Feels a little silly to add an extra system call
> > for that. I agree the void * isn't the prettiest thing in the world, but
> > at least it allows us to extend the API without having to add even more
> > system calls down the line.
>
> With the __u64 changes, we end up with this:
>
> struct io_uring_register_buffers {
>         __u64 iovecs;           /* pointer to iovecs array */
>         __u32 nr_iovecs;        /* number of iovecs in array */
>         __u32 pad;
> };
>
> struct io_uring_register_files {
>         __u64 fds;
>         __u32 nr_fds;
>         __u32 pad;
> };
>
> which are identical. So the question then becomes if I should just make
> these opaque enough to be the same thing, ala:
>
> struct io_uring_register_data {
>         __u64 data;
>         __u32 nr_elems;
>         __u32 pad;
> };

Right, that looks good in either form.

> and then probably add a bit more reserved space so we have something
> that can be extended...

Or maybe go the opposite way and pass the two members you have
directly to the system call:

int io_uring_register(unsigned int fd, unsigned int opcode, void
__user *, arg, unsigned count)
{
      ...
}

Where 'arg' now points to the array of iovecs or the the array of file
descriptors, or whatever else you need.

       Arnd

Re: [PATCH 13/16] io_uring: add support for pre-mapped user IO buffers

[Jens Axboe]

On 1/16/19 8:41 AM, Arnd Bergmann wrote:
> On Wed, Jan 16, 2019 at 4:32 PM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> On 1/16/19 8:14 AM, Jens Axboe wrote:
>>> On 1/16/19 3:53 AM, Arnd Bergmann wrote:
>>>> On Tue, Jan 15, 2019 at 3:56 AM Jens Axboe <axboe@kernel.dk> wrote:
>>>>
>>>>> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
>>>>> index 542757a4c898..e36c264d74e8 100644
>>>>> --- a/include/linux/syscalls.h
>>>>> +++ b/include/linux/syscalls.h
>>>>> @@ -314,6 +314,8 @@ asmlinkage long sys_io_uring_setup(u32 entries,
>>>>>                                 struct io_uring_params __user *p);
>>>>>  asmlinkage long sys_io_uring_enter(unsigned int fd, u32 to_submit,
>>>>>                                 u32 min_complete, u32 flags);
>>>>> +asmlinkage long sys_io_uring_register(unsigned int fd, unsigned op,
>>>>> +                               void __user *arg);
>>>>>
>>>>
>>>> Would it be possible to make this a typed pointer instead? If this needs to
>>>> be extended later to pass a different structure, a new system call may
>>>> be better for consistency than overloading the argument in various
>>>> ways.
>>>
>>> As you can see from the later patch for registering files, it'll be used
>>> for other structs too. Feels a little silly to add an extra system call
>>> for that. I agree the void * isn't the prettiest thing in the world, but
>>> at least it allows us to extend the API without having to add even more
>>> system calls down the line.
>>
>> With the __u64 changes, we end up with this:
>>
>> struct io_uring_register_buffers {
>>         __u64 iovecs;           /* pointer to iovecs array */
>>         __u32 nr_iovecs;        /* number of iovecs in array */
>>         __u32 pad;
>> };
>>
>> struct io_uring_register_files {
>>         __u64 fds;
>>         __u32 nr_fds;
>>         __u32 pad;
>> };
>>
>> which are identical. So the question then becomes if I should just make
>> these opaque enough to be the same thing, ala:
>>
>> struct io_uring_register_data {
>>         __u64 data;
>>         __u32 nr_elems;
>>         __u32 pad;
>> };
> 
> Right, that looks good in either form.
> 
>> and then probably add a bit more reserved space so we have something
>> that can be extended...
> 
> Or maybe go the opposite way and pass the two members you have
> directly to the system call:
> 
> int io_uring_register(unsigned int fd, unsigned int opcode, void
> __user *, arg, unsigned count)
> {
>       ...
> }
> 
> Where 'arg' now points to the array of iovecs or the the array of file
> descriptors, or whatever else you need.

I kind of like that, that gets rid of having to wrap it in a struct. If
I later wanted to abuse it, arg could point to a struct...

I'll make this change.

-- 
Jens Axboe

[PATCH 03/16] block: add bio_set_polled() helper

[Jens Axboe]

For the upcoming async polled IO, we can't sleep allocating requests.
If we do, then we introduce a deadlock where the submitter already
has async polled IO in-flight, but can't wait for them to complete
since polled requests must be active found and reaped.

Utilize the helper in the blockdev DIRECT_IO code.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/block_dev.c      |  4 ++--
 include/linux/bio.h | 14 ++++++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 5415579f3e14..2ebd2a0d7789 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -233,7 +233,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
 		task_io_account_write(ret);
 	}
 	if (iocb->ki_flags & IOCB_HIPRI)
-		bio.bi_opf |= REQ_HIPRI;
+		bio_set_polled(&bio, iocb);
 
 	qc = submit_bio(&bio);
 	for (;;) {
@@ -401,7 +401,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
 		nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES);
 		if (!nr_pages) {
 			if (iocb->ki_flags & IOCB_HIPRI)
-				bio->bi_opf |= REQ_HIPRI;
+				bio_set_polled(bio, iocb);
 
 			qc = submit_bio(bio);
 			WRITE_ONCE(iocb->ki_cookie, qc);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 7380b094dcca..f6f0a2b3cbc8 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -823,5 +823,19 @@ static inline int bio_integrity_add_page(struct bio *bio, struct page *page,
 
 #endif /* CONFIG_BLK_DEV_INTEGRITY */
 
+/*
+ * Mark a bio as polled. Note that for async polled IO, the caller must
+ * expect -EWOULDBLOCK if we cannot allocate a request (or other resources).
+ * We cannot block waiting for requests on polled IO, as those completions
+ * must be found by the caller. This is different than IRQ driven IO, where
+ * it's safe to wait for IO to complete.
+ */
+static inline void bio_set_polled(struct bio *bio, struct kiocb *kiocb)
+{
+	bio->bi_opf |= REQ_HIPRI;
+	if (!is_sync_kiocb(kiocb))
+		bio->bi_opf |= REQ_NOWAIT;
+}
+
 #endif /* CONFIG_BLOCK */
 #endif /* __LINUX_BIO_H */
-- 
2.17.1

Re: [PATCH 03/16] block: add bio_set_polled() helper

[Jens Axboe]

On 1/10/19 2:43 AM, Ming Lei wrote:
> On Tue, Jan 08, 2019 at 09:56:32AM -0700, Jens Axboe wrote:
>> For the upcoming async polled IO, we can't sleep allocating requests.
>> If we do, then we introduce a deadlock where the submitter already
>> has async polled IO in-flight, but can't wait for them to complete
>> since polled requests must be active found and reaped.
>>
>> Utilize the helper in the blockdev DIRECT_IO code.
>>
>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>> ---
>>  fs/block_dev.c      |  4 ++--
>>  include/linux/bio.h | 14 ++++++++++++++
>>  2 files changed, 16 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/block_dev.c b/fs/block_dev.c
>> index 5415579f3e14..2ebd2a0d7789 100644
>> --- a/fs/block_dev.c
>> +++ b/fs/block_dev.c
>> @@ -233,7 +233,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
>>  		task_io_account_write(ret);
>>  	}
>>  	if (iocb->ki_flags & IOCB_HIPRI)
>> -		bio.bi_opf |= REQ_HIPRI;
>> +		bio_set_polled(&bio, iocb);
>>  
>>  	qc = submit_bio(&bio);
>>  	for (;;) {
>> @@ -401,7 +401,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>>  		nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES);
>>  		if (!nr_pages) {
>>  			if (iocb->ki_flags & IOCB_HIPRI)
>> -				bio->bi_opf |= REQ_HIPRI;
>> +				bio_set_polled(bio, iocb);
>>  
>>  			qc = submit_bio(bio);
>>  			WRITE_ONCE(iocb->ki_cookie, qc);
>> diff --git a/include/linux/bio.h b/include/linux/bio.h
>> index 7380b094dcca..f6f0a2b3cbc8 100644
>> --- a/include/linux/bio.h
>> +++ b/include/linux/bio.h
>> @@ -823,5 +823,19 @@ static inline int bio_integrity_add_page(struct bio *bio, struct page *page,
>>  
>>  #endif /* CONFIG_BLK_DEV_INTEGRITY */
>>  
>> +/*
>> + * Mark a bio as polled. Note that for async polled IO, the caller must
>> + * expect -EWOULDBLOCK if we cannot allocate a request (or other resources).
>> + * We cannot block waiting for requests on polled IO, as those completions
>> + * must be found by the caller. This is different than IRQ driven IO, where
>> + * it's safe to wait for IO to complete.
>> + */
>> +static inline void bio_set_polled(struct bio *bio, struct kiocb *kiocb)
>> +{
>> +	bio->bi_opf |= REQ_HIPRI;
>> +	if (!is_sync_kiocb(kiocb))
>> +		bio->bi_opf |= REQ_NOWAIT;
>> +}
>> +
> 
> REQ_NOWAIT doesn't cover allocating split bio, is that a issue?

Yes, that might be an issue. I'll look into what we should do about that,
for now it's not a huge problem.

> BTW, could you explain a bit about the deadlock in case of sleep from
> request allocation?

It's more a live lock I guess, but the issue is that with polled IO, we don't
get an IRQ. For normal IO, if you run out, you can just sleep and wait for
an IRQ to come in, trigger a completion (or multiple), which will then wake
you up. For polled IO, you have to find those completions. Hence if you just
go to sleep, nobody is going to find those completions for you. You'll then
be waiting forever for an event, that will never trigger.

-- 
Jens Axboe

Re: [PATCH 03/16] block: add bio_set_polled() helper

[Ming Lei]

On Tue, Jan 08, 2019 at 09:56:32AM -0700, Jens Axboe wrote:
> For the upcoming async polled IO, we can't sleep allocating requests.
> If we do, then we introduce a deadlock where the submitter already
> has async polled IO in-flight, but can't wait for them to complete
> since polled requests must be active found and reaped.
> 
> Utilize the helper in the blockdev DIRECT_IO code.
> 
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>  fs/block_dev.c      |  4 ++--
>  include/linux/bio.h | 14 ++++++++++++++
>  2 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 5415579f3e14..2ebd2a0d7789 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -233,7 +233,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
>  		task_io_account_write(ret);
>  	}
>  	if (iocb->ki_flags & IOCB_HIPRI)
> -		bio.bi_opf |= REQ_HIPRI;
> +		bio_set_polled(&bio, iocb);
>  
>  	qc = submit_bio(&bio);
>  	for (;;) {
> @@ -401,7 +401,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>  		nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES);
>  		if (!nr_pages) {
>  			if (iocb->ki_flags & IOCB_HIPRI)
> -				bio->bi_opf |= REQ_HIPRI;
> +				bio_set_polled(bio, iocb);
>  
>  			qc = submit_bio(bio);
>  			WRITE_ONCE(iocb->ki_cookie, qc);
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index 7380b094dcca..f6f0a2b3cbc8 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -823,5 +823,19 @@ static inline int bio_integrity_add_page(struct bio *bio, struct page *page,
>  
>  #endif /* CONFIG_BLK_DEV_INTEGRITY */
>  
> +/*
> + * Mark a bio as polled. Note that for async polled IO, the caller must
> + * expect -EWOULDBLOCK if we cannot allocate a request (or other resources).
> + * We cannot block waiting for requests on polled IO, as those completions
> + * must be found by the caller. This is different than IRQ driven IO, where
> + * it's safe to wait for IO to complete.
> + */
> +static inline void bio_set_polled(struct bio *bio, struct kiocb *kiocb)
> +{
> +	bio->bi_opf |= REQ_HIPRI;
> +	if (!is_sync_kiocb(kiocb))
> +		bio->bi_opf |= REQ_NOWAIT;
> +}
> +

REQ_NOWAIT doesn't cover allocating split bio, is that a issue?

BTW, could you explain a bit about the deadlock in case of sleep from
request allocation?

Thanks,
Ming

[PATCH 03/16] block: add bio_set_polled() helper

[Jens Axboe]

For the upcoming async polled IO, we can't sleep allocating requests.
If we do, then we introduce a deadlock where the submitter already
has async polled IO in-flight, but can't wait for them to complete
since polled requests must be active found and reaped.

Utilize the helper in the blockdev DIRECT_IO code.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/block_dev.c      |  4 ++--
 include/linux/bio.h | 14 ++++++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 5415579f3e14..2ebd2a0d7789 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -233,7 +233,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
 		task_io_account_write(ret);
 	}
 	if (iocb->ki_flags & IOCB_HIPRI)
-		bio.bi_opf |= REQ_HIPRI;
+		bio_set_polled(&bio, iocb);
 
 	qc = submit_bio(&bio);
 	for (;;) {
@@ -401,7 +401,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
 		nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES);
 		if (!nr_pages) {
 			if (iocb->ki_flags & IOCB_HIPRI)
-				bio->bi_opf |= REQ_HIPRI;
+				bio_set_polled(bio, iocb);
 
 			qc = submit_bio(bio);
 			WRITE_ONCE(iocb->ki_cookie, qc);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 7380b094dcca..f6f0a2b3cbc8 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -823,5 +823,19 @@ static inline int bio_integrity_add_page(struct bio *bio, struct page *page,
 
 #endif /* CONFIG_BLK_DEV_INTEGRITY */
 
+/*
+ * Mark a bio as polled. Note that for async polled IO, the caller must
+ * expect -EWOULDBLOCK if we cannot allocate a request (or other resources).
+ * We cannot block waiting for requests on polled IO, as those completions
+ * must be found by the caller. This is different than IRQ driven IO, where
+ * it's safe to wait for IO to complete.
+ */
+static inline void bio_set_polled(struct bio *bio, struct kiocb *kiocb)
+{
+	bio->bi_opf |= REQ_HIPRI;
+	if (!is_sync_kiocb(kiocb))
+		bio->bi_opf |= REQ_NOWAIT;
+}
+
 #endif /* CONFIG_BLOCK */
 #endif /* __LINUX_BIO_H */
-- 
2.17.1