[PATCH v17 0/6] Introducing trace buffer mapping by user-space

[PATCH v17 0/6] Introducing trace buffer mapping by user-space

[Vincent Donnefort]

The tracing ring-buffers can be stored on disk or sent to network
without any copy via splice. However the later doesn't allow real time
processing of the traces. A solution is to give userspace direct access
to the ring-buffer pages via a mapping. An application can now become a
consumer of the ring-buffer, in a similar fashion to what trace_pipe
offers.

Support for this new feature can already be found in libtracefs from
version 1.8, when built with EXTRA_CFLAGS=-DFORCE_MMAP_ENABLE.

Vincent

v16 -> v17:
  * Documentation and comments improvements.
  * Create get/put_snapshot_map() for clearer code.
  * Replace kzalloc with kcalloc.
  * Fix -ENOMEM handling in rb_alloc_meta_page().
  * Move flush(cpu_buffer->reader_page) behind the reader lock.
  * Move all inc/dec of cpu_buffer->mapped behind reader lock and buffer
    mutex. (removes READ_ONCE/WRITE_ONCE accesses).

v15 -> v16:
  * Add comment for the dcache flush.
  * Remove now unnecessary WRITE_ONCE for the meta-page.

v14 -> v15:
  * Add meta-page and reader-page flush. Intends to fix the mapping
    for VIVT and aliasing-VIPT data caches.
  * -EPERM on VM_EXEC.
  * Fix build warning !CONFIG_TRACER_MAX_TRACE.

v13 -> v14:
  * All cpu_buffer->mapped readers use READ_ONCE (except for swap_cpu)
  * on unmap, sync meta-page teardown with the reader_lock instead of
    the synchronize_rcu.
  * Add a dedicated spinlock for trace_array ->snapshot and ->mapped.
    (intends to fix a lockdep issue)
  * Add kerneldoc for flags and Reserved fields.
  * Add kselftest for snapshot/map mutual exclusion.

v12 -> v13:
  * Swap subbufs_{touched,lost} for Reserved fields.
  * Add a flag field in the meta-page.
  * Fix CONFIG_TRACER_MAX_TRACE.
  * Rebase on top of trace/urgent.
  * Add a comment for try_unregister_trigger()

v11 -> v12:
  * Fix code sample mmap bug.
  * Add logging in sample code.
  * Reset tracer in selftest.
  * Add a refcount for the snapshot users.
  * Prevent mapping when there are snapshot users and vice versa.
  * Refine the meta-page.
  * Fix types in the meta-page.
  * Collect Reviewed-by.

v10 -> v11:
  * Add Documentation and code sample.
  * Add a selftest.
  * Move all the update to the meta-page into a single
    rb_update_meta_page().
  * rb_update_meta_page() is now called from
    ring_buffer_map_get_reader() to fix NOBLOCK callers.
  * kerneldoc for struct trace_meta_page.
  * Add a patch to zero all the ring-buffer allocations.

v9 -> v10:
  * Refactor rb_update_meta_page()
  * In-loop declaration for foreach_subbuf_page()
  * Check for cpu_buffer->mapped overflow

v8 -> v9:
  * Fix the unlock path in ring_buffer_map()
  * Fix cpu_buffer cast with rb_work_rq->is_cpu_buffer
  * Rebase on linux-trace/for-next (3cb3091138ca0921c4569bcf7ffa062519639b6a)

v7 -> v8:
  * Drop the subbufs renaming into bpages
  * Use subbuf as a name when relevant

v6 -> v7:
  * Rebase onto lore.kernel.org/lkml/20231215175502.106587604@goodmis.org/
  * Support for subbufs
  * Rename subbufs into bpages

v5 -> v6:
  * Rebase on next-20230802.
  * (unsigned long) -> (void *) cast for virt_to_page().
  * Add a wait for the GET_READER_PAGE ioctl.
  * Move writer fields update (overrun/pages_lost/entries/pages_touched)
    in the irq_work.
  * Rearrange id in struct buffer_page.
  * Rearrange the meta-page.
  * ring_buffer_meta_page -> trace_buffer_meta_page.
  * Add meta_struct_len into the meta-page.

v4 -> v5:
  * Trivial rebase onto 6.5-rc3 (previously 6.4-rc3)

v3 -> v4:
  * Add to the meta-page:
       - pages_lost / pages_read (allow to compute how full is the
	 ring-buffer)
       - read (allow to compute how many entries can be read)
       - A reader_page struct.
  * Rename ring_buffer_meta_header -> ring_buffer_meta
  * Rename ring_buffer_get_reader_page -> ring_buffer_map_get_reader_page
  * Properly consume events on ring_buffer_map_get_reader_page() with
    rb_advance_reader().

v2 -> v3:
  * Remove data page list (for non-consuming read)
    ** Implies removing order > 0 meta-page
  * Add a new meta page field ->read
  * Rename ring_buffer_meta_page_header into ring_buffer_meta_header

v1 -> v2:
  * Hide data_pages from the userspace struct
  * Fix META_PAGE_MAX_PAGES
  * Support for order > 0 meta-page
  * Add missing page->mapping.

Vincent Donnefort (6):
  ring-buffer: Zero ring-buffer sub-buffers
  ring-buffer: Introducing ring-buffer mapping functions
  tracing: Add snapshot refcount
  tracing: Allow user-space mapping of the ring-buffer
  Documentation: tracing: Add ring-buffer mapping
  ring-buffer/selftest: Add ring-buffer mapping test

 Documentation/trace/index.rst                 |   1 +
 Documentation/trace/ring-buffer-map.rst       | 106 +++++
 include/linux/ring_buffer.h                   |   7 +
 include/uapi/linux/trace_mmap.h               |  48 +++
 kernel/trace/ring_buffer.c                    | 385 +++++++++++++++++-
 kernel/trace/trace.c                          | 234 ++++++++++-
 kernel/trace/trace.h                          |   9 +-
 kernel/trace/trace_events_trigger.c           |  58 ++-
 tools/testing/selftests/ring-buffer/Makefile  |   8 +
 tools/testing/selftests/ring-buffer/config    |   2 +
 .../testing/selftests/ring-buffer/map_test.c  | 273 +++++++++++++
 11 files changed, 1085 insertions(+), 46 deletions(-)
 create mode 100644 Documentation/trace/ring-buffer-map.rst
 create mode 100644 include/uapi/linux/trace_mmap.h
 create mode 100644 tools/testing/selftests/ring-buffer/Makefile
 create mode 100644 tools/testing/selftests/ring-buffer/config
 create mode 100644 tools/testing/selftests/ring-buffer/map_test.c


base-commit: ca185770db914869ff9fe773bac5e0e5e4165b83
-- 
2.43.0.687.g38aa6559b0-goog

[PATCH v17 1/6] ring-buffer: Zero ring-buffer sub-buffers

[Vincent Donnefort]

In preparation for the ring-buffer memory mapping where each subbuf will
be accessible to user-space, zero all the page allocations.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index fd4bfe3ecf01..ca796675c0a1 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1472,7 +1472,8 @@ static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
 
 		list_add(&bpage->list, pages);
 
-		page = alloc_pages_node(cpu_to_node(cpu_buffer->cpu), mflags,
+		page = alloc_pages_node(cpu_to_node(cpu_buffer->cpu),
+					mflags | __GFP_ZERO,
 					cpu_buffer->buffer->subbuf_order);
 		if (!page)
 			goto free_pages;
@@ -1557,7 +1558,8 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
 
 	cpu_buffer->reader_page = bpage;
 
-	page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, cpu_buffer->buffer->subbuf_order);
+	page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL | __GFP_ZERO,
+				cpu_buffer->buffer->subbuf_order);
 	if (!page)
 		goto fail_free_reader;
 	bpage->page = page_address(page);
@@ -5525,7 +5527,8 @@ ring_buffer_alloc_read_page(struct trace_buffer *buffer, int cpu)
 	if (bpage->data)
 		goto out;
 
-	page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL | __GFP_NORETRY,
+	page = alloc_pages_node(cpu_to_node(cpu),
+				GFP_KERNEL | __GFP_NORETRY | __GFP_ZERO,
 				cpu_buffer->buffer->subbuf_order);
 	if (!page) {
 		kfree(bpage);
-- 
2.43.0.687.g38aa6559b0-goog

[PATCH v17 2/6] ring-buffer: Introducing ring-buffer mapping functions

[Vincent Donnefort]

In preparation for allowing the user-space to map a ring-buffer, add
a set of mapping functions:

  ring_buffer_{map,unmap}()
  ring_buffer_map_fault()

And controls on the ring-buffer:

  ring_buffer_map_get_reader()  /* swap reader and head */

Mapping the ring-buffer also involves:

  A unique ID for each subbuf of the ring-buffer, currently they are
  only identified through their in-kernel VA.

  A meta-page, where are stored ring-buffer statistics and a
  description for the current reader

The linear mapping exposes the meta-page, and each subbuf of the
ring-buffer, ordered following their unique ID, assigned during the
first mapping.

Once mapped, no subbuf can get in or out of the ring-buffer: the buffer
size will remain unmodified and the splice enabling functions will in
reality simply memcpy the data instead of swapping subbufs.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index fa802db216f9..0841ba8bab14 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -6,6 +6,8 @@
 #include <linux/seq_file.h>
 #include <linux/poll.h>
 
+#include <uapi/linux/trace_mmap.h>
+
 struct trace_buffer;
 struct ring_buffer_iter;
 
@@ -221,4 +223,9 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node);
 #define trace_rb_cpu_prepare	NULL
 #endif
 
+int ring_buffer_map(struct trace_buffer *buffer, int cpu);
+int ring_buffer_unmap(struct trace_buffer *buffer, int cpu);
+struct page *ring_buffer_map_fault(struct trace_buffer *buffer, int cpu,
+				   unsigned long pgoff);
+int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu);
 #endif /* _LINUX_RING_BUFFER_H */
diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h
new file mode 100644
index 000000000000..ffcd8dfcaa4f
--- /dev/null
+++ b/include/uapi/linux/trace_mmap.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _TRACE_MMAP_H_
+#define _TRACE_MMAP_H_
+
+#include <linux/types.h>
+
+/**
+ * struct trace_buffer_meta - Ring-buffer Meta-page description
+ * @meta_page_size:	Size of this meta-page.
+ * @meta_struct_len:	Size of this structure.
+ * @subbuf_size:	Size of each sub-buffer.
+ * @nr_subbufs:		Number of subbfs in the ring-buffer, including the reader.
+ * @reader.lost_events:	Number of events lost at the time of the reader swap.
+ * @reader.id:		subbuf ID of the current reader. ID range [0 : @nr_subbufs - 1]
+ * @reader.read:	Number of bytes read on the reader subbuf.
+ * @flags:		Placeholder for now, 0 until new features are supported.
+ * @entries:		Number of entries in the ring-buffer.
+ * @overrun:		Number of entries lost in the ring-buffer.
+ * @read:		Number of entries that have been read.
+ * @Reserved1:		Reserved for future use.
+ * @Reserved2:		Reserved for future use.
+ */
+struct trace_buffer_meta {
+	__u32		meta_page_size;
+	__u32		meta_struct_len;
+
+	__u32		subbuf_size;
+	__u32		nr_subbufs;
+
+	struct {
+		__u64	lost_events;
+		__u32	id;
+		__u32	read;
+	} reader;
+
+	__u64	flags;
+
+	__u64	entries;
+	__u64	overrun;
+	__u64	read;
+
+	__u64	Reserved1;
+	__u64	Reserved2;
+};
+
+#endif /* _TRACE_MMAP_H_ */
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index ca796675c0a1..8d4f4b88cba2 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -9,6 +9,7 @@
 #include <linux/ring_buffer.h>
 #include <linux/trace_clock.h>
 #include <linux/sched/clock.h>
+#include <linux/cacheflush.h>
 #include <linux/trace_seq.h>
 #include <linux/spinlock.h>
 #include <linux/irq_work.h>
@@ -338,6 +339,7 @@ struct buffer_page {
 	local_t		 entries;	/* entries on this page */
 	unsigned long	 real_end;	/* real end of data */
 	unsigned	 order;		/* order of the page */
+	u32		 id;		/* ID for external mapping */
 	struct buffer_data_page *page;	/* Actual data page */
 };
 
@@ -484,6 +486,12 @@ struct ring_buffer_per_cpu {
 	u64				read_stamp;
 	/* pages removed since last reset */
 	unsigned long			pages_removed;
+
+	unsigned int			mapped;
+	struct mutex			mapping_lock;
+	unsigned long			*subbuf_ids;	/* ID to subbuf addr */
+	struct trace_buffer_meta	*meta_page;
+
 	/* ring buffer pages to update, > 0 to add, < 0 to remove */
 	long				nr_pages_to_update;
 	struct list_head		new_pages; /* new pages to add */
@@ -1548,6 +1556,7 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
 	init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
 	init_waitqueue_head(&cpu_buffer->irq_work.waiters);
 	init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
+	mutex_init(&cpu_buffer->mapping_lock);
 
 	bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
 			    GFP_KERNEL, cpu_to_node(cpu));
@@ -1738,8 +1747,6 @@ bool ring_buffer_time_stamp_abs(struct trace_buffer *buffer)
 	return buffer->time_stamp_abs;
 }
 
-static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
-
 static inline unsigned long rb_page_entries(struct buffer_page *bpage)
 {
 	return local_read(&bpage->entries) & RB_WRITE_MASK;
@@ -5160,6 +5167,22 @@ static void rb_clear_buffer_page(struct buffer_page *page)
 	page->read = 0;
 }
 
+static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct trace_buffer_meta *meta = cpu_buffer->meta_page;
+
+	meta->reader.read = cpu_buffer->reader_page->read;
+	meta->reader.id = cpu_buffer->reader_page->id;
+	meta->reader.lost_events = cpu_buffer->lost_events;
+
+	meta->entries = local_read(&cpu_buffer->entries);
+	meta->overrun = local_read(&cpu_buffer->overrun);
+	meta->read = cpu_buffer->read;
+
+	/* Some archs do not have data cache coherency between kernel and user-space */
+	flush_dcache_folio(virt_to_folio(cpu_buffer->meta_page));
+}
+
 static void
 rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
 {
@@ -5204,6 +5227,9 @@ rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
 	cpu_buffer->lost_events = 0;
 	cpu_buffer->last_overrun = 0;
 
+	if (cpu_buffer->mapped)
+		rb_update_meta_page(cpu_buffer);
+
 	rb_head_page_activate(cpu_buffer);
 	cpu_buffer->pages_removed = 0;
 }
@@ -5418,6 +5444,12 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer_a,
 	cpu_buffer_a = buffer_a->buffers[cpu];
 	cpu_buffer_b = buffer_b->buffers[cpu];
 
+	/* It's up to the callers to not try to swap mapped buffers */
+	if (WARN_ON_ONCE(cpu_buffer_a->mapped || cpu_buffer_b->mapped)) {
+		ret = -EBUSY;
+		goto out;
+	}
+
 	/* At least make sure the two buffers are somewhat the same */
 	if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
 		goto out;
@@ -5682,7 +5714,8 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
 	 * Otherwise, we can simply swap the page with the one passed in.
 	 */
 	if (read || (len < (commit - read)) ||
-	    cpu_buffer->reader_page == cpu_buffer->commit_page) {
+	    cpu_buffer->reader_page == cpu_buffer->commit_page ||
+	    cpu_buffer->mapped) {
 		struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
 		unsigned int rpos = read;
 		unsigned int pos = 0;
@@ -5901,6 +5934,11 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
 
 		cpu_buffer = buffer->buffers[cpu];
 
+		if (cpu_buffer->mapped) {
+			err = -EBUSY;
+			goto error;
+		}
+
 		/* Update the number of pages to match the new size */
 		nr_pages = old_size * buffer->buffers[cpu]->nr_pages;
 		nr_pages = DIV_ROUND_UP(nr_pages, buffer->subbuf_size);
@@ -6002,6 +6040,338 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
 }
 EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set);
 
+#define subbuf_page(off, start) \
+	virt_to_page((void *)(start + (off << PAGE_SHIFT)))
+
+#define foreach_subbuf_page(sub_order, start, page)		\
+	page = subbuf_page(0, (start));				\
+	for (int __off = 0; __off < (1 << (sub_order));		\
+	     __off++, page = subbuf_page(__off, (start)))
+
+static inline void subbuf_map_prepare(unsigned long subbuf_start, int order)
+{
+	struct page *page;
+
+	/*
+	 * When allocating order > 0 pages, only the first struct page has a
+	 * refcount > 1. Increasing the refcount here ensures none of the struct
+	 * page composing the sub-buffer is freeed when the mapping is closed.
+	 */
+	foreach_subbuf_page(order, subbuf_start, page)
+		page_ref_inc(page);
+}
+
+static inline void subbuf_unmap(unsigned long subbuf_start, int order)
+{
+	struct page *page;
+
+	foreach_subbuf_page(order, subbuf_start, page) {
+		page_ref_dec(page);
+		page->mapping = NULL;
+	}
+}
+
+static void rb_free_subbuf_ids(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	int sub_id;
+
+	for (sub_id = 0; sub_id < cpu_buffer->nr_pages + 1; sub_id++)
+		subbuf_unmap(cpu_buffer->subbuf_ids[sub_id],
+			     cpu_buffer->buffer->subbuf_order);
+
+	kfree(cpu_buffer->subbuf_ids);
+	cpu_buffer->subbuf_ids = NULL;
+}
+
+static int rb_alloc_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	struct page *page;
+
+	if (cpu_buffer->meta_page)
+		return 0;
+
+	page = alloc_page(GFP_USER | __GFP_ZERO);
+	if (!page)
+		return -ENOMEM;
+
+	cpu_buffer->meta_page = page_to_virt(page);
+
+	return 0;
+}
+
+static void rb_free_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	unsigned long addr = (unsigned long)cpu_buffer->meta_page;
+
+	if (!addr)
+		return;
+
+	virt_to_page((void *)addr)->mapping = NULL;
+	free_page(addr);
+	cpu_buffer->meta_page = NULL;
+}
+
+static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
+				   unsigned long *subbuf_ids)
+{
+	struct trace_buffer_meta *meta = cpu_buffer->meta_page;
+	unsigned int nr_subbufs = cpu_buffer->nr_pages + 1;
+	struct buffer_page *first_subbuf, *subbuf;
+	int id = 0;
+
+	subbuf_ids[id] = (unsigned long)cpu_buffer->reader_page->page;
+	subbuf_map_prepare(subbuf_ids[id], cpu_buffer->buffer->subbuf_order);
+	cpu_buffer->reader_page->id = id++;
+
+	first_subbuf = subbuf = rb_set_head_page(cpu_buffer);
+	do {
+		if (WARN_ON(id >= nr_subbufs))
+			break;
+
+		subbuf_ids[id] = (unsigned long)subbuf->page;
+		subbuf->id = id;
+		subbuf_map_prepare(subbuf_ids[id], cpu_buffer->buffer->subbuf_order);
+
+		rb_inc_page(&subbuf);
+		id++;
+	} while (subbuf != first_subbuf);
+
+	/* install subbuf ID to kern VA translation */
+	cpu_buffer->subbuf_ids = subbuf_ids;
+
+	meta->meta_page_size = PAGE_SIZE;
+	meta->meta_struct_len = sizeof(*meta);
+	meta->nr_subbufs = nr_subbufs;
+	meta->subbuf_size = cpu_buffer->buffer->subbuf_size + BUF_PAGE_HDR_SIZE;
+
+	rb_update_meta_page(cpu_buffer);
+}
+
+static inline struct ring_buffer_per_cpu *
+rb_get_mapped_buffer(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return ERR_PTR(-EINVAL);
+
+	cpu_buffer = buffer->buffers[cpu];
+
+	mutex_lock(&cpu_buffer->mapping_lock);
+
+	if (!cpu_buffer->mapped) {
+		mutex_unlock(&cpu_buffer->mapping_lock);
+		return ERR_PTR(-ENODEV);
+	}
+
+	return cpu_buffer;
+}
+
+static inline void rb_put_mapped_buffer(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	mutex_unlock(&cpu_buffer->mapping_lock);
+}
+
+/*
+ * Fast-path for rb_buffer_(un)map(). Called whenever the meta-page doesn't need
+ * to be set-up or torn-down.
+ */
+static int __rb_inc_dec_mapped(struct trace_buffer *buffer,
+			       struct ring_buffer_per_cpu *cpu_buffer,
+			       bool inc)
+{
+	unsigned long flags;
+
+	lockdep_assert_held(cpu_buffer->mapping_lock);
+
+	if (inc && cpu_buffer->mapped == UINT_MAX)
+		return -EBUSY;
+
+	if (WARN_ON(!inc && cpu_buffer->mapped == 0))
+		return -EINVAL;
+
+	mutex_lock(&buffer->mutex);
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
+	if (inc)
+		cpu_buffer->mapped++;
+	else
+		cpu_buffer->mapped--;
+
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+	mutex_unlock(&buffer->mutex);
+
+	return 0;
+}
+
+int ring_buffer_map(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long flags, *subbuf_ids;
+	int err = 0;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return -EINVAL;
+
+	cpu_buffer = buffer->buffers[cpu];
+
+	mutex_lock(&cpu_buffer->mapping_lock);
+
+	if (cpu_buffer->mapped) {
+		err = __rb_inc_dec_mapped(buffer, cpu_buffer, true);
+		mutex_unlock(&cpu_buffer->mapping_lock);
+		return err;
+	}
+
+	/* prevent another thread from changing buffer/sub-buffer sizes */
+	mutex_lock(&buffer->mutex);
+
+	err = rb_alloc_meta_page(cpu_buffer);
+	if (err)
+		goto unlock;
+
+	/* subbuf_ids include the reader while nr_pages does not */
+	subbuf_ids = kcalloc(cpu_buffer->nr_pages + 1, sizeof(*subbuf_ids), GFP_KERNEL);
+	if (!subbuf_ids) {
+		rb_free_meta_page(cpu_buffer);
+		err = -ENOMEM;
+		goto unlock;
+	}
+
+	atomic_inc(&cpu_buffer->resize_disabled);
+
+	/*
+	 * Lock all readers to block any subbuf swap until the subbuf IDs are
+	 * assigned.
+	 */
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
+	rb_setup_ids_meta_page(cpu_buffer, subbuf_ids);
+	cpu_buffer->mapped = 1;
+
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+unlock:
+	mutex_unlock(&buffer->mutex);
+	mutex_unlock(&cpu_buffer->mapping_lock);
+
+	return err;
+}
+
+int ring_buffer_unmap(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long flags;
+	int err = 0;
+
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return -EINVAL;
+
+	cpu_buffer = buffer->buffers[cpu];
+
+	mutex_lock(&cpu_buffer->mapping_lock);
+
+	if (!cpu_buffer->mapped) {
+		err = -ENODEV;
+		goto out;
+	} else if (cpu_buffer->mapped > 1) {
+		__rb_inc_dec_mapped(buffer, cpu_buffer, false);
+		goto out;
+	}
+
+	mutex_lock(&buffer->mutex);
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+
+	cpu_buffer->mapped = 0;
+
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+
+	rb_free_subbuf_ids(cpu_buffer);
+	rb_free_meta_page(cpu_buffer);
+	atomic_dec(&cpu_buffer->resize_disabled);
+
+	mutex_unlock(&buffer->mutex);
+out:
+	mutex_unlock(&cpu_buffer->mapping_lock);
+
+	return err;
+}
+
+/*
+ *   +--------------+  pgoff == 0
+ *   |   meta page  |
+ *   +--------------+  pgoff == 1
+ *   | subbuffer 0  |
+ *   +--------------+  pgoff == 1 + (1 << subbuf_order)
+ *   | subbuffer 1  |
+ *         ...
+ */
+struct page *ring_buffer_map_fault(struct trace_buffer *buffer, int cpu,
+				   unsigned long pgoff)
+{
+	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
+	unsigned long subbuf_id, subbuf_offset, addr;
+	struct page *page;
+
+	if (!pgoff)
+		return virt_to_page((void *)cpu_buffer->meta_page);
+
+	pgoff--;
+
+	subbuf_id = pgoff >> buffer->subbuf_order;
+	if (subbuf_id > cpu_buffer->nr_pages)
+		return NULL;
+
+	subbuf_offset = pgoff & ((1UL << buffer->subbuf_order) - 1);
+	addr = cpu_buffer->subbuf_ids[subbuf_id] + (subbuf_offset * PAGE_SIZE);
+	page = virt_to_page((void *)addr);
+
+	return page;
+}
+
+int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu)
+{
+	struct ring_buffer_per_cpu *cpu_buffer;
+	unsigned long reader_size;
+	unsigned long flags;
+
+	cpu_buffer = rb_get_mapped_buffer(buffer, cpu);
+	if (IS_ERR(cpu_buffer))
+		return (int)PTR_ERR(cpu_buffer);
+
+	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
+consume:
+	if (rb_per_cpu_empty(cpu_buffer))
+		goto out;
+
+	reader_size = rb_page_size(cpu_buffer->reader_page);
+
+	/*
+	 * There are data to be read on the current reader page, we can
+	 * return to the caller. But before that, we assume the latter will read
+	 * everything. Let's update the kernel reader accordingly.
+	 */
+	if (cpu_buffer->reader_page->read < reader_size) {
+		while (cpu_buffer->reader_page->read < reader_size)
+			rb_advance_reader(cpu_buffer);
+		goto out;
+	}
+
+	if (WARN_ON(!rb_get_reader_page(cpu_buffer)))
+		goto out;
+
+	goto consume;
+out:
+	/* Some archs do not have data cache coherency between kernel and user-space */
+	flush_dcache_folio(virt_to_folio(cpu_buffer->reader_page->page));
+
+	rb_update_meta_page(cpu_buffer);
+
+	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
+	rb_put_mapped_buffer(cpu_buffer);
+
+	return 0;
+}
+
 /*
  * We only allocate new buffers, never free them if the CPU goes down.
  * If we were to free the buffer, then the user would lose any trace that was in
-- 
2.43.0.687.g38aa6559b0-goog

[PATCH v17 3/6] tracing: Add snapshot refcount

[Vincent Donnefort]

When a ring-buffer is memory mapped by user-space, no trace or
ring-buffer swap is possible. This means the snapshot feature is
mutually exclusive with the memory mapping. Having a refcount on
snapshot users will help to know if a mapping is possible or not.

Instead of relying on the global trace_types_lock, a new spinlock is
introduced to serialize accesses to trace_array->snapshot. This intends
to allow access to that variable in a context where the mmap lock is
already held.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2a7c6fd934e9..4ebf4d0bd14c 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1300,6 +1300,50 @@ static void free_snapshot(struct trace_array *tr)
 	tr->allocated_snapshot = false;
 }
 
+static int tracing_arm_snapshot_locked(struct trace_array *tr)
+{
+	int ret;
+
+	lockdep_assert_held(&trace_types_lock);
+
+	spin_lock(&tr->snapshot_trigger_lock);
+	if (tr->snapshot == UINT_MAX) {
+		spin_unlock(&tr->snapshot_trigger_lock);
+		return -EBUSY;
+	}
+
+	tr->snapshot++;
+	spin_unlock(&tr->snapshot_trigger_lock);
+
+	ret = tracing_alloc_snapshot_instance(tr);
+	if (ret) {
+		spin_lock(&tr->snapshot_trigger_lock);
+		tr->snapshot--;
+		spin_unlock(&tr->snapshot_trigger_lock);
+	}
+
+	return ret;
+}
+
+int tracing_arm_snapshot(struct trace_array *tr)
+{
+	int ret;
+
+	mutex_lock(&trace_types_lock);
+	ret = tracing_arm_snapshot_locked(tr);
+	mutex_unlock(&trace_types_lock);
+
+	return ret;
+}
+
+void tracing_disarm_snapshot(struct trace_array *tr)
+{
+	spin_lock(&tr->snapshot_trigger_lock);
+	if (!WARN_ON(!tr->snapshot))
+		tr->snapshot--;
+	spin_unlock(&tr->snapshot_trigger_lock);
+}
+
 /**
  * tracing_alloc_snapshot - allocate snapshot buffer.
  *
@@ -1373,10 +1417,6 @@ int tracing_snapshot_cond_enable(struct trace_array *tr, void *cond_data,
 
 	mutex_lock(&trace_types_lock);
 
-	ret = tracing_alloc_snapshot_instance(tr);
-	if (ret)
-		goto fail_unlock;
-
 	if (tr->current_trace->use_max_tr) {
 		ret = -EBUSY;
 		goto fail_unlock;
@@ -1395,6 +1435,10 @@ int tracing_snapshot_cond_enable(struct trace_array *tr, void *cond_data,
 		goto fail_unlock;
 	}
 
+	ret = tracing_arm_snapshot_locked(tr);
+	if (ret)
+		goto fail_unlock;
+
 	local_irq_disable();
 	arch_spin_lock(&tr->max_lock);
 	tr->cond_snapshot = cond_snapshot;
@@ -1439,6 +1483,8 @@ int tracing_snapshot_cond_disable(struct trace_array *tr)
 	arch_spin_unlock(&tr->max_lock);
 	local_irq_enable();
 
+	tracing_disarm_snapshot(tr);
+
 	return ret;
 }
 EXPORT_SYMBOL_GPL(tracing_snapshot_cond_disable);
@@ -1481,6 +1527,7 @@ int tracing_snapshot_cond_disable(struct trace_array *tr)
 }
 EXPORT_SYMBOL_GPL(tracing_snapshot_cond_disable);
 #define free_snapshot(tr)	do { } while (0)
+#define tracing_arm_snapshot_locked(tr) ({ -EBUSY; })
 #endif /* CONFIG_TRACER_SNAPSHOT */
 
 void tracer_tracing_off(struct trace_array *tr)
@@ -6593,11 +6640,12 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
 		 */
 		synchronize_rcu();
 		free_snapshot(tr);
+		tracing_disarm_snapshot(tr);
 	}
 
-	if (t->use_max_tr && !tr->allocated_snapshot) {
-		ret = tracing_alloc_snapshot_instance(tr);
-		if (ret < 0)
+	if (t->use_max_tr) {
+		ret = tracing_arm_snapshot_locked(tr);
+		if (ret)
 			goto out;
 	}
 #else
@@ -6606,8 +6654,13 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
 
 	if (t->init) {
 		ret = tracer_init(t, tr);
-		if (ret)
+		if (ret) {
+#ifdef CONFIG_TRACER_MAX_TRACE
+			if (t->use_max_tr)
+				tracing_disarm_snapshot(tr);
+#endif
 			goto out;
+		}
 	}
 
 	tr->current_trace = t;
@@ -7709,10 +7762,11 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
 		if (tr->allocated_snapshot)
 			ret = resize_buffer_duplicate_size(&tr->max_buffer,
 					&tr->array_buffer, iter->cpu_file);
-		else
-			ret = tracing_alloc_snapshot_instance(tr);
-		if (ret < 0)
+
+		ret = tracing_arm_snapshot_locked(tr);
+		if (ret)
 			break;
+
 		/* Now, we're going to swap */
 		if (iter->cpu_file == RING_BUFFER_ALL_CPUS) {
 			local_irq_disable();
@@ -7722,6 +7776,7 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
 			smp_call_function_single(iter->cpu_file, tracing_swap_cpu_buffer,
 						 (void *)tr, 1);
 		}
+		tracing_disarm_snapshot(tr);
 		break;
 	default:
 		if (tr->allocated_snapshot) {
@@ -8846,8 +8901,13 @@ ftrace_trace_snapshot_callback(struct trace_array *tr, struct ftrace_hash *hash,
 
 	ops = param ? &snapshot_count_probe_ops :  &snapshot_probe_ops;
 
-	if (glob[0] == '!')
-		return unregister_ftrace_function_probe_func(glob+1, tr, ops);
+	if (glob[0] == '!') {
+		ret = unregister_ftrace_function_probe_func(glob+1, tr, ops);
+		if (!ret)
+			tracing_disarm_snapshot(tr);
+
+		return ret;
+	}
 
 	if (!param)
 		goto out_reg;
@@ -8866,12 +8926,13 @@ ftrace_trace_snapshot_callback(struct trace_array *tr, struct ftrace_hash *hash,
 		return ret;
 
  out_reg:
-	ret = tracing_alloc_snapshot_instance(tr);
+	ret = tracing_arm_snapshot(tr);
 	if (ret < 0)
 		goto out;
 
 	ret = register_ftrace_function_probe(glob, tr, ops, count);
-
+	if (ret < 0)
+		tracing_disarm_snapshot(tr);
  out:
 	return ret < 0 ? ret : 0;
 }
@@ -9678,7 +9739,9 @@ trace_array_create_systems(const char *name, const char *systems)
 	raw_spin_lock_init(&tr->start_lock);
 
 	tr->max_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
-
+#ifdef CONFIG_TRCER_MAX_TRACE
+	spinlock_init(&tr->snapshot_trigger_lock);
+#endif
 	tr->current_trace = &nop_trace;
 
 	INIT_LIST_HEAD(&tr->systems);
@@ -10648,7 +10711,9 @@ __init static int tracer_alloc_buffers(void)
 	global_trace.current_trace = &nop_trace;
 
 	global_trace.max_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
-
+#ifdef CONFIG_TRACER_MAX_TRACE
+	spin_lock_init(&global_trace.snapshot_trigger_lock);
+#endif
 	ftrace_init_global_array_ops(&global_trace);
 
 	init_trace_flags_index(&global_trace);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 00f873910c5d..bd312e9afe25 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -334,8 +334,8 @@ struct trace_array {
 	 */
 	struct array_buffer	max_buffer;
 	bool			allocated_snapshot;
-#endif
-#ifdef CONFIG_TRACER_MAX_TRACE
+	spinlock_t		snapshot_trigger_lock;
+	unsigned int		snapshot;
 	unsigned long		max_latency;
 #ifdef CONFIG_FSNOTIFY
 	struct dentry		*d_max_latency;
@@ -1973,12 +1973,16 @@ static inline void trace_event_eval_update(struct trace_eval_map **map, int len)
 #ifdef CONFIG_TRACER_SNAPSHOT
 void tracing_snapshot_instance(struct trace_array *tr);
 int tracing_alloc_snapshot_instance(struct trace_array *tr);
+int tracing_arm_snapshot(struct trace_array *tr);
+void tracing_disarm_snapshot(struct trace_array *tr);
 #else
 static inline void tracing_snapshot_instance(struct trace_array *tr) { }
 static inline int tracing_alloc_snapshot_instance(struct trace_array *tr)
 {
 	return 0;
 }
+static inline int tracing_arm_snapshot(struct trace_array *tr) { return 0; }
+static inline void tracing_disarm_snapshot(struct trace_array *tr) { }
 #endif
 
 #ifdef CONFIG_PREEMPT_TRACER
diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index b33c3861fbbb..62e4f58b8671 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -597,20 +597,12 @@ static int register_trigger(char *glob,
 	return ret;
 }
 
-/**
- * unregister_trigger - Generic event_command @unreg implementation
- * @glob: The raw string used to register the trigger
- * @test: Trigger-specific data used to find the trigger to remove
- * @file: The trace_event_file associated with the event
- *
- * Common implementation for event trigger unregistration.
- *
- * Usually used directly as the @unreg method in event command
- * implementations.
+/*
+ * True if the trigger was found and unregistered, else false.
  */
-static void unregister_trigger(char *glob,
-			       struct event_trigger_data *test,
-			       struct trace_event_file *file)
+static bool try_unregister_trigger(char *glob,
+				   struct event_trigger_data *test,
+				   struct trace_event_file *file)
 {
 	struct event_trigger_data *data = NULL, *iter;
 
@@ -626,8 +618,32 @@ static void unregister_trigger(char *glob,
 		}
 	}
 
-	if (data && data->ops->free)
-		data->ops->free(data);
+	if (data) {
+		if (data->ops->free)
+			data->ops->free(data);
+
+		return true;
+	}
+
+	return false;
+}
+
+/**
+ * unregister_trigger - Generic event_command @unreg implementation
+ * @glob: The raw string used to register the trigger
+ * @test: Trigger-specific data used to find the trigger to remove
+ * @file: The trace_event_file associated with the event
+ *
+ * Common implementation for event trigger unregistration.
+ *
+ * Usually used directly as the @unreg method in event command
+ * implementations.
+ */
+static void unregister_trigger(char *glob,
+			       struct event_trigger_data *test,
+			       struct trace_event_file *file)
+{
+	try_unregister_trigger(glob, test, file);
 }
 
 /*
@@ -1470,7 +1486,7 @@ register_snapshot_trigger(char *glob,
 			  struct event_trigger_data *data,
 			  struct trace_event_file *file)
 {
-	int ret = tracing_alloc_snapshot_instance(file->tr);
+	int ret = tracing_arm_snapshot(file->tr);
 
 	if (ret < 0)
 		return ret;
@@ -1478,6 +1494,14 @@ register_snapshot_trigger(char *glob,
 	return register_trigger(glob, data, file);
 }
 
+static void unregister_snapshot_trigger(char *glob,
+					struct event_trigger_data *data,
+					struct trace_event_file *file)
+{
+	if (try_unregister_trigger(glob, data, file))
+		tracing_disarm_snapshot(file->tr);
+}
+
 static int
 snapshot_trigger_print(struct seq_file *m, struct event_trigger_data *data)
 {
@@ -1510,7 +1534,7 @@ static struct event_command trigger_snapshot_cmd = {
 	.trigger_type		= ETT_SNAPSHOT,
 	.parse			= event_trigger_parse,
 	.reg			= register_snapshot_trigger,
-	.unreg			= unregister_trigger,
+	.unreg			= unregister_snapshot_trigger,
 	.get_trigger_ops	= snapshot_get_trigger_ops,
 	.set_filter		= set_trigger_filter,
 };
-- 
2.43.0.687.g38aa6559b0-goog

[PATCH v17 4/6] tracing: Allow user-space mapping of the ring-buffer

[Vincent Donnefort]

Currently, user-space extracts data from the ring-buffer via splice,
which is handy for storage or network sharing. However, due to splice
limitations, it is imposible to do real-time analysis without a copy.

A solution for that problem is to let the user-space map the ring-buffer
directly.

The mapping is exposed via the per-CPU file trace_pipe_raw. The first
element of the mapping is the meta-page. It is followed by each
subbuffer constituting the ring-buffer, ordered by their unique page ID:

  * Meta-page -- include/uapi/linux/trace_mmap.h for a description
  * Subbuf ID 0
  * Subbuf ID 1
     ...

It is therefore easy to translate a subbuf ID into an offset in the
mapping:

  reader_id = meta->reader->id;
  reader_offset = meta->meta_page_size + reader_id * meta->subbuf_size;

When new data is available, the mapper must call a newly introduced ioctl:
TRACE_MMAP_IOCTL_GET_READER. This will update the Meta-page reader ID to
point to the next reader containing unread data.

Mapping will prevent snapshot and buffer size modifications.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h
index ffcd8dfcaa4f..d25b9d504a7c 100644
--- a/include/uapi/linux/trace_mmap.h
+++ b/include/uapi/linux/trace_mmap.h
@@ -43,4 +43,6 @@ struct trace_buffer_meta {
 	__u64	Reserved2;
 };
 
+#define TRACE_MMAP_IOCTL_GET_READER		_IO('T', 0x1)
+
 #endif /* _TRACE_MMAP_H_ */
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4ebf4d0bd14c..c9e513a95cb7 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1175,6 +1175,12 @@ static void tracing_snapshot_instance_cond(struct trace_array *tr,
 		return;
 	}
 
+	if (tr->mapped) {
+		trace_array_puts(tr, "*** BUFFER MEMORY MAPPED ***\n");
+		trace_array_puts(tr, "*** Can not use snapshot (sorry) ***\n");
+		return;
+	}
+
 	local_irq_save(flags);
 	update_max_tr(tr, current, smp_processor_id(), cond_data);
 	local_irq_restore(flags);
@@ -1307,7 +1313,7 @@ static int tracing_arm_snapshot_locked(struct trace_array *tr)
 	lockdep_assert_held(&trace_types_lock);
 
 	spin_lock(&tr->snapshot_trigger_lock);
-	if (tr->snapshot == UINT_MAX) {
+	if (tr->snapshot == UINT_MAX || tr->mapped) {
 		spin_unlock(&tr->snapshot_trigger_lock);
 		return -EBUSY;
 	}
@@ -6533,7 +6539,7 @@ static void tracing_set_nop(struct trace_array *tr)
 {
 	if (tr->current_trace == &nop_trace)
 		return;
-	
+
 	tr->current_trace->enabled--;
 
 	if (tr->current_trace->reset)
@@ -8652,15 +8658,31 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
 	return ret;
 }
 
-/* An ioctl call with cmd 0 to the ring buffer file will wake up all waiters */
 static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
 	struct ftrace_buffer_info *info = file->private_data;
 	struct trace_iterator *iter = &info->iter;
+	int err;
+
+	if (cmd == TRACE_MMAP_IOCTL_GET_READER) {
+		if (!(file->f_flags & O_NONBLOCK)) {
+			err = ring_buffer_wait(iter->array_buffer->buffer,
+					       iter->cpu_file,
+					       iter->tr->buffer_percent);
+			if (err)
+				return err;
+		}
 
-	if (cmd)
-		return -ENOIOCTLCMD;
+		return ring_buffer_map_get_reader(iter->array_buffer->buffer,
+						  iter->cpu_file);
+	} else if (cmd) {
+		return -ENOTTY;
+	}
 
+	/*
+	 * An ioctl call with cmd 0 to the ring buffer file will wake up all
+	 * waiters
+	 */
 	mutex_lock(&trace_types_lock);
 
 	iter->wait_index++;
@@ -8673,6 +8695,110 @@ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned
 	return 0;
 }
 
+static vm_fault_t tracing_buffers_mmap_fault(struct vm_fault *vmf)
+{
+	struct ftrace_buffer_info *info = vmf->vma->vm_file->private_data;
+	struct trace_iterator *iter = &info->iter;
+	vm_fault_t ret = VM_FAULT_SIGBUS;
+	struct page *page;
+
+	page = ring_buffer_map_fault(iter->array_buffer->buffer, iter->cpu_file,
+				     vmf->pgoff);
+	if (!page)
+		return ret;
+
+	get_page(page);
+	vmf->page = page;
+	vmf->page->mapping = vmf->vma->vm_file->f_mapping;
+	vmf->page->index = vmf->pgoff;
+
+	return 0;
+}
+
+#ifdef CONFIG_TRACER_MAX_TRACE
+static int get_snapshot_map(struct trace_array *tr)
+{
+	int err = 0;
+
+	/*
+	 * Called with mmap_lock held. lockdep would be unhappy if we would now
+	 * take trace_types_lock. Instead use the specific
+	 * snapshot_trigger_lock.
+	 */
+	spin_lock(&tr->snapshot_trigger_lock);
+
+	if (tr->snapshot || tr->mapped == UINT_MAX)
+		err = -EBUSY;
+	else
+		tr->mapped++;
+
+	spin_unlock(&tr->snapshot_trigger_lock);
+
+	/* Wait for update_max_tr() to observe iter->tr->mapped */
+	if (tr->mapped == 1)
+		synchronize_rcu();
+
+	return err;
+
+}
+static void put_snapshot_map(struct trace_array *tr)
+{
+	spin_lock(&tr->snapshot_trigger_lock);
+	if (!WARN_ON(!tr->mapped))
+		tr->mapped--;
+	spin_unlock(&tr->snapshot_trigger_lock);
+}
+#else
+static inline int get_snapshot_map(struct trace_array *tr) { return 0; }
+static inline void put_snapshot_map(struct trace_array *tr) { }
+#endif
+
+static void tracing_buffers_mmap_close(struct vm_area_struct *vma)
+{
+	struct ftrace_buffer_info *info = vma->vm_file->private_data;
+	struct trace_iterator *iter = &info->iter;
+
+	ring_buffer_unmap(iter->array_buffer->buffer, iter->cpu_file);
+	put_snapshot_map(iter->tr);
+}
+
+static void tracing_buffers_mmap_open(struct vm_area_struct *vma)
+{
+	struct ftrace_buffer_info *info = vma->vm_file->private_data;
+	struct trace_iterator *iter = &info->iter;
+
+	WARN_ON(ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file));
+}
+
+static const struct vm_operations_struct tracing_buffers_vmops = {
+	.open		= tracing_buffers_mmap_open,
+	.close		= tracing_buffers_mmap_close,
+	.fault		= tracing_buffers_mmap_fault,
+};
+
+static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+	struct ftrace_buffer_info *info = filp->private_data;
+	struct trace_iterator *iter = &info->iter;
+	int ret = 0;
+
+	if (vma->vm_flags & VM_WRITE || vma->vm_flags & VM_EXEC)
+		return -EPERM;
+
+	vm_flags_mod(vma, VM_DONTCOPY | VM_DONTDUMP, VM_MAYWRITE);
+	vma->vm_ops = &tracing_buffers_vmops;
+
+	ret = get_snapshot_map(iter->tr);
+	if (ret)
+		return ret;
+
+	ret = ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file);
+	if (ret)
+		put_snapshot_map(iter->tr);
+
+	return ret;
+}
+
 static const struct file_operations tracing_buffers_fops = {
 	.open		= tracing_buffers_open,
 	.read		= tracing_buffers_read,
@@ -8681,6 +8807,7 @@ static const struct file_operations tracing_buffers_fops = {
 	.splice_read	= tracing_buffers_splice_read,
 	.unlocked_ioctl = tracing_buffers_ioctl,
 	.llseek		= no_llseek,
+	.mmap		= tracing_buffers_mmap,
 };
 
 static ssize_t
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index bd312e9afe25..8a96e7a89e6b 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -336,6 +336,7 @@ struct trace_array {
 	bool			allocated_snapshot;
 	spinlock_t		snapshot_trigger_lock;
 	unsigned int		snapshot;
+	unsigned int		mapped;
 	unsigned long		max_latency;
 #ifdef CONFIG_FSNOTIFY
 	struct dentry		*d_max_latency;
-- 
2.43.0.687.g38aa6559b0-goog

[PATCH v17 5/6] Documentation: tracing: Add ring-buffer mapping

[Vincent Donnefort]

It is now possible to mmap() a ring-buffer to stream its content. Add
some documentation and a code example.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst
index 5092d6c13af5..0b300901fd75 100644
--- a/Documentation/trace/index.rst
+++ b/Documentation/trace/index.rst
@@ -29,6 +29,7 @@ Linux Tracing Technologies
    timerlat-tracer
    intel_th
    ring-buffer-design
+   ring-buffer-map
    stm
    sys-t
    coresight/index
diff --git a/Documentation/trace/ring-buffer-map.rst b/Documentation/trace/ring-buffer-map.rst
new file mode 100644
index 000000000000..0426ab4bcf3d
--- /dev/null
+++ b/Documentation/trace/ring-buffer-map.rst
@@ -0,0 +1,106 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==================================
+Tracefs ring-buffer memory mapping
+==================================
+
+:Author: Vincent Donnefort <vdonnefort@google.com>
+
+Overview
+========
+Tracefs ring-buffer memory map provides an efficient method to stream data
+as no memory copy is necessary. The application mapping the ring-buffer becomes
+then a consumer for that ring-buffer, in a similar fashion to trace_pipe.
+
+Memory mapping setup
+====================
+The mapping works with a mmap() of the trace_pipe_raw interface.
+
+The first system page of the mapping contains ring-buffer statistics and
+description. It is referred as the meta-page. One of the most important field of
+the meta-page is the reader. It contains the sub-buffer ID which can be safely
+read by the mapper (see ring-buffer-design.rst).
+
+The meta-page is followed by all the sub-buffers, ordered by ascendant ID. It is
+therefore effortless to know where the reader starts in the mapping:
+
+.. code-block:: c
+
+        reader_id = meta->reader->id;
+        reader_offset = meta->meta_page_size + reader_id * meta->subbuf_size;
+
+When the application is done with the current reader, it can get a new one using
+the trace_pipe_raw ioctl() TRACE_MMAP_IOCTL_GET_READER. This ioctl also updates
+the meta-page fields.
+
+Limitations
+===========
+When a mapping is in place on a Tracefs ring-buffer, it is not possible to
+either resize it (either by increasing the entire size of the ring-buffer or
+each subbuf). It is also not possible to use snapshot and causes splice to copy
+the ring buffer data instead of using the copyless swap from the ring buffer.
+
+Concurrent readers (either another application mapping that ring-buffer or the
+kernel with trace_pipe) are allowed but not recommended. They will compete for
+the ring-buffer and the output is unpredictable, just like concurrent readers on
+trace_pipe would be.
+
+Example
+=======
+
+.. code-block:: c
+
+        #include <fcntl.h>
+        #include <stdio.h>
+        #include <stdlib.h>
+        #include <unistd.h>
+
+        #include <linux/trace_mmap.h>
+
+        #include <sys/mman.h>
+        #include <sys/ioctl.h>
+
+        #define TRACE_PIPE_RAW "/sys/kernel/tracing/per_cpu/cpu0/trace_pipe_raw"
+
+        int main(void)
+        {
+                int page_size = getpagesize(), fd, reader_id;
+                unsigned long meta_len, data_len;
+                struct trace_buffer_meta *meta;
+                void *map, *reader, *data;
+
+                fd = open(TRACE_PIPE_RAW, O_RDONLY | O_NONBLOCK);
+                if (fd < 0)
+                        exit(EXIT_FAILURE);
+
+                map = mmap(NULL, page_size, PROT_READ, MAP_SHARED, fd, 0);
+                if (map == MAP_FAILED)
+                        exit(EXIT_FAILURE);
+
+                meta = (struct trace_buffer_meta *)map;
+                meta_len = meta->meta_page_size;
+
+                printf("entries:        %llu\n", meta->entries);
+                printf("overrun:        %llu\n", meta->overrun);
+                printf("read:           %llu\n", meta->read);
+                printf("nr_subbufs:     %u\n", meta->nr_subbufs);
+
+                data_len = meta->subbuf_size * meta->nr_subbufs;
+                data = mmap(NULL, data_len, PROT_READ, MAP_SHARED, fd, meta_len);
+                if (data == MAP_FAILED)
+                        exit(EXIT_FAILURE);
+
+                if (ioctl(fd, TRACE_MMAP_IOCTL_GET_READER) < 0)
+                        exit(EXIT_FAILURE);
+
+                reader_id = meta->reader.id;
+                reader = data + meta->subbuf_size * reader_id;
+
+                printf("Current reader address: %p\n", reader);
+
+                munmap(data, data_len);
+                munmap(meta, meta_len);
+                close (fd);
+
+                return 0;
+        }
-- 
2.43.0.687.g38aa6559b0-goog

[PATCH v17 6/6] ring-buffer/selftest: Add ring-buffer mapping test

[Vincent Donnefort]

This test maps a ring-buffer and validate the meta-page after reset and
after emitting few events.

Cc: Shuah Khan <shuah@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: linux-kselftest@vger.kernel.org
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/tools/testing/selftests/ring-buffer/Makefile b/tools/testing/selftests/ring-buffer/Makefile
new file mode 100644
index 000000000000..627c5fa6d1ab
--- /dev/null
+++ b/tools/testing/selftests/ring-buffer/Makefile
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0
+CFLAGS += -Wl,-no-as-needed -Wall
+CFLAGS += $(KHDR_INCLUDES)
+CFLAGS += -D_GNU_SOURCE
+
+TEST_GEN_PROGS = map_test
+
+include ../lib.mk
diff --git a/tools/testing/selftests/ring-buffer/config b/tools/testing/selftests/ring-buffer/config
new file mode 100644
index 000000000000..d936f8f00e78
--- /dev/null
+++ b/tools/testing/selftests/ring-buffer/config
@@ -0,0 +1,2 @@
+CONFIG_FTRACE=y
+CONFIG_TRACER_SNAPSHOT=y
diff --git a/tools/testing/selftests/ring-buffer/map_test.c b/tools/testing/selftests/ring-buffer/map_test.c
new file mode 100644
index 000000000000..56c44b29d998
--- /dev/null
+++ b/tools/testing/selftests/ring-buffer/map_test.c
@@ -0,0 +1,273 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Ring-buffer memory mapping tests
+ *
+ * Copyright (c) 2024 Vincent Donnefort <vdonnefort@google.com>
+ */
+#include <fcntl.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include <linux/trace_mmap.h>
+
+#include <sys/mman.h>
+#include <sys/ioctl.h>
+
+#include "../user_events/user_events_selftests.h" /* share tracefs setup */
+#include "../kselftest_harness.h"
+
+#define TRACEFS_ROOT "/sys/kernel/tracing"
+
+static int __tracefs_write(const char *path, const char *value)
+{
+	int fd, ret;
+
+	fd = open(path, O_WRONLY | O_TRUNC);
+	if (fd < 0)
+		return fd;
+
+	ret = write(fd, value, strlen(value));
+
+	close(fd);
+
+	return ret == -1 ? -errno : 0;
+}
+
+static int __tracefs_write_int(const char *path, int value)
+{
+	char *str;
+	int ret;
+
+	if (asprintf(&str, "%d", value) < 0)
+		return -1;
+
+	ret = __tracefs_write(path, str);
+
+	free(str);
+
+	return ret;
+}
+
+#define tracefs_write_int(path, value) \
+	ASSERT_EQ(__tracefs_write_int((path), (value)), 0)
+
+#define tracefs_write(path, value) \
+	ASSERT_EQ(__tracefs_write((path), (value)), 0)
+
+static int tracefs_reset(void)
+{
+	if (__tracefs_write_int(TRACEFS_ROOT"/tracing_on", 0))
+		return -1;
+	if (__tracefs_write(TRACEFS_ROOT"/trace", ""))
+		return -1;
+	if (__tracefs_write(TRACEFS_ROOT"/set_event", ""))
+		return -1;
+	if (__tracefs_write(TRACEFS_ROOT"/current_tracer", "nop"))
+		return -1;
+
+	return 0;
+}
+
+struct tracefs_cpu_map_desc {
+	struct trace_buffer_meta	*meta;
+	void				*data;
+	int				cpu_fd;
+};
+
+int tracefs_cpu_map(struct tracefs_cpu_map_desc *desc, int cpu)
+{
+	unsigned long meta_len, data_len;
+	int page_size = getpagesize();
+	char *cpu_path;
+	void *map;
+
+	if (asprintf(&cpu_path,
+		     TRACEFS_ROOT"/per_cpu/cpu%d/trace_pipe_raw",
+		     cpu) < 0)
+		return -ENOMEM;
+
+	desc->cpu_fd = open(cpu_path, O_RDONLY | O_NONBLOCK);
+	free(cpu_path);
+	if (desc->cpu_fd < 0)
+		return -ENODEV;
+
+	map = mmap(NULL, page_size, PROT_READ, MAP_SHARED, desc->cpu_fd, 0);
+	if (map == MAP_FAILED)
+		return -errno;
+
+	desc->meta = (struct trace_buffer_meta *)map;
+
+	meta_len = desc->meta->meta_page_size;
+	data_len = desc->meta->subbuf_size * desc->meta->nr_subbufs;
+
+	map = mmap(NULL, data_len, PROT_READ, MAP_SHARED, desc->cpu_fd, meta_len);
+	if (map == MAP_FAILED) {
+		munmap(desc->meta, desc->meta->meta_page_size);
+		return -EINVAL;
+	}
+
+	desc->data = map;
+
+	return 0;
+}
+
+void tracefs_cpu_unmap(struct tracefs_cpu_map_desc *desc)
+{
+	munmap(desc->data, desc->meta->subbuf_size * desc->meta->nr_subbufs);
+	munmap(desc->meta, desc->meta->meta_page_size);
+	close(desc->cpu_fd);
+}
+
+FIXTURE(map) {
+	struct tracefs_cpu_map_desc	map_desc;
+	bool				umount;
+};
+
+FIXTURE_VARIANT(map) {
+	int	subbuf_size;
+};
+
+FIXTURE_VARIANT_ADD(map, subbuf_size_4k) {
+	.subbuf_size = 4,
+};
+
+FIXTURE_VARIANT_ADD(map, subbuf_size_8k) {
+	.subbuf_size = 8,
+};
+
+FIXTURE_SETUP(map)
+{
+	int cpu = sched_getcpu();
+	cpu_set_t cpu_mask;
+	bool fail, umount;
+	char *message;
+
+	if (!tracefs_enabled(&message, &fail, &umount)) {
+		if (fail) {
+			TH_LOG("Tracefs setup failed: %s", message);
+			ASSERT_FALSE(fail);
+		}
+		SKIP(return, "Skipping: %s", message);
+	}
+
+	self->umount = umount;
+
+	ASSERT_GE(cpu, 0);
+
+	ASSERT_EQ(tracefs_reset(), 0);
+
+	tracefs_write_int(TRACEFS_ROOT"/buffer_subbuf_size_kb", variant->subbuf_size);
+
+	ASSERT_EQ(tracefs_cpu_map(&self->map_desc, cpu), 0);
+
+	/*
+	 * Ensure generated events will be found on this very same ring-buffer.
+	 */
+	CPU_ZERO(&cpu_mask);
+	CPU_SET(cpu, &cpu_mask);
+	ASSERT_EQ(sched_setaffinity(0, sizeof(cpu_mask), &cpu_mask), 0);
+}
+
+FIXTURE_TEARDOWN(map)
+{
+	tracefs_reset();
+
+	if (self->umount)
+		tracefs_unmount();
+
+	tracefs_cpu_unmap(&self->map_desc);
+}
+
+TEST_F(map, meta_page_check)
+{
+	struct tracefs_cpu_map_desc *desc = &self->map_desc;
+	int cnt = 0;
+
+	ASSERT_EQ(desc->meta->entries, 0);
+	ASSERT_EQ(desc->meta->overrun, 0);
+	ASSERT_EQ(desc->meta->read, 0);
+
+	ASSERT_EQ(desc->meta->reader.id, 0);
+	ASSERT_EQ(desc->meta->reader.read, 0);
+
+	ASSERT_EQ(ioctl(desc->cpu_fd, TRACE_MMAP_IOCTL_GET_READER), 0);
+	ASSERT_EQ(desc->meta->reader.id, 0);
+
+	tracefs_write_int(TRACEFS_ROOT"/tracing_on", 1);
+	for (int i = 0; i < 16; i++)
+		tracefs_write_int(TRACEFS_ROOT"/trace_marker", i);
+again:
+	ASSERT_EQ(ioctl(desc->cpu_fd, TRACE_MMAP_IOCTL_GET_READER), 0);
+
+	ASSERT_EQ(desc->meta->entries, 16);
+	ASSERT_EQ(desc->meta->overrun, 0);
+	ASSERT_EQ(desc->meta->read, 16);
+
+	ASSERT_EQ(desc->meta->reader.id, 1);
+
+	if (!(cnt++))
+		goto again;
+}
+
+FIXTURE(snapshot) {
+	bool	umount;
+};
+
+FIXTURE_SETUP(snapshot)
+{
+	bool fail, umount;
+	struct stat sb;
+	char *message;
+
+	if (stat(TRACEFS_ROOT"/snapshot", &sb))
+		SKIP(return, "Skipping: %s", "snapshot not available");
+
+	if (!tracefs_enabled(&message, &fail, &umount)) {
+		if (fail) {
+			TH_LOG("Tracefs setup failed: %s", message);
+			ASSERT_FALSE(fail);
+		}
+		SKIP(return, "Skipping: %s", message);
+	}
+
+	self->umount = umount;
+}
+
+FIXTURE_TEARDOWN(snapshot)
+{
+	__tracefs_write(TRACEFS_ROOT"/events/sched/sched_switch/trigger",
+			"!snapshot");
+	tracefs_reset();
+
+	if (self->umount)
+		tracefs_unmount();
+}
+
+TEST_F(snapshot, excludes_map)
+{
+	struct tracefs_cpu_map_desc map_desc;
+	int cpu = sched_getcpu();
+
+	ASSERT_GE(cpu, 0);
+	tracefs_write(TRACEFS_ROOT"/events/sched/sched_switch/trigger",
+		      "snapshot");
+	ASSERT_EQ(tracefs_cpu_map(&map_desc, cpu), -EBUSY);
+}
+
+TEST_F(snapshot, excluded_by_map)
+{
+	struct tracefs_cpu_map_desc map_desc;
+	int cpu = sched_getcpu();
+
+	ASSERT_EQ(tracefs_cpu_map(&map_desc, cpu), 0);
+
+	ASSERT_EQ(__tracefs_write(TRACEFS_ROOT"/events/sched/sched_switch/trigger",
+				  "snapshot"), -EBUSY);
+	ASSERT_EQ(__tracefs_write(TRACEFS_ROOT"/snapshot",
+				  "1"), -EBUSY);
+}
+
+TEST_HARNESS_MAIN
-- 
2.43.0.687.g38aa6559b0-goog

Re: [PATCH v17 2/6] ring-buffer: Introducing ring-buffer mapping functions

[Steven Rostedt]

On Tue, 13 Feb 2024 11:49:41 +0000
Vincent Donnefort <vdonnefort@google.com> wrote:

Did you test with lockdep?

> +static int __rb_inc_dec_mapped(struct trace_buffer *buffer,
> +			       struct ring_buffer_per_cpu *cpu_buffer,
> +			       bool inc)
> +{
> +	unsigned long flags;
> +
> +	lockdep_assert_held(cpu_buffer->mapping_lock);

/work/git/linux-trace.git/kernel/trace/ring_buffer.c: In function ‘__rb_inc_dec_mapped’:
/work/git/linux-trace.git/include/linux/lockdep.h:234:61: error: invalid type argument of ‘->’ (have ‘struct mutex’)
  234 | #define lockdep_is_held(lock)           lock_is_held(&(lock)->dep_map)
      |                                                             ^~
/work/git/linux-trace.git/include/asm-generic/bug.h:123:32: note: in definition of macro ‘WARN_ON’
  123 |         int __ret_warn_on = !!(condition);                              \
      |                                ^~~~~~~~~
/work/git/linux-trace.git/include/linux/lockdep.h:267:9: note: in expansion of macro ‘lockdep_assert’
  267 |         lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
      |         ^~~~~~~~~~~~~~
/work/git/linux-trace.git/include/linux/lockdep.h:267:24: note: in expansion of macro ‘lockdep_is_held’
  267 |         lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
      |                        ^~~~~~~~~~~~~~~
/work/git/linux-trace.git/kernel/trace/ring_buffer.c:6167:9: note: in expansion of macro ‘lockdep_assert_held’
 6167 |         lockdep_assert_held(cpu_buffer->mapping_lock);
      |         ^~~~~~~~~~~~~~~~~~~

I believe that is supposed to be:

	lockdep_assert_held(&cpu_buffer->mapping_lock);

-- Steve

> +
> +	if (inc && cpu_buffer->mapped == UINT_MAX)
> +		return -EBUSY;
> +
> +	if (WARN_ON(!inc && cpu_buffer->mapped == 0))
> +		return -EINVAL;
> +
> +	mutex_lock(&buffer->mutex);
> +	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
> +
> +	if (inc)
> +		cpu_buffer->mapped++;
> +	else
> +		cpu_buffer->mapped--;
> +
> +	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
> +	mutex_unlock(&buffer->mutex);
> +
> +	return 0;
> +}

Re: [PATCH v17 2/6] ring-buffer: Introducing ring-buffer mapping functions

[Steven Rostedt]

On Tue, 13 Feb 2024 15:53:09 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 13 Feb 2024 11:49:41 +0000
> Vincent Donnefort <vdonnefort@google.com> wrote:
> 
> Did you test with lockdep?
> 
> > +static int __rb_inc_dec_mapped(struct trace_buffer *buffer,
> > +			       struct ring_buffer_per_cpu *cpu_buffer,
> > +			       bool inc)
> > +{
> > +	unsigned long flags;
> > +
> > +	lockdep_assert_held(cpu_buffer->mapping_lock);  
> 
> /work/git/linux-trace.git/kernel/trace/ring_buffer.c: In function ‘__rb_inc_dec_mapped’:
> /work/git/linux-trace.git/include/linux/lockdep.h:234:61: error: invalid type argument of ‘->’ (have ‘struct mutex’)
>   234 | #define lockdep_is_held(lock)           lock_is_held(&(lock)->dep_map)
>       |                                                             ^~
> /work/git/linux-trace.git/include/asm-generic/bug.h:123:32: note: in definition of macro ‘WARN_ON’
>   123 |         int __ret_warn_on = !!(condition);                              \
>       |                                ^~~~~~~~~
> /work/git/linux-trace.git/include/linux/lockdep.h:267:9: note: in expansion of macro ‘lockdep_assert’
>   267 |         lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
>       |         ^~~~~~~~~~~~~~
> /work/git/linux-trace.git/include/linux/lockdep.h:267:24: note: in expansion of macro ‘lockdep_is_held’
>   267 |         lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
>       |                        ^~~~~~~~~~~~~~~
> /work/git/linux-trace.git/kernel/trace/ring_buffer.c:6167:9: note: in expansion of macro ‘lockdep_assert_held’
>  6167 |         lockdep_assert_held(cpu_buffer->mapping_lock);
>       |         ^~~~~~~~~~~~~~~~~~~
> 
> I believe that is supposed to be:
> 
> 	lockdep_assert_held(&cpu_buffer->mapping_lock);

If this is the only issue with this series, I may just fix up the patch
myself.

Re: [PATCH v17 2/6] ring-buffer: Introducing ring-buffer mapping functions

[kernel test robot]

Hi Vincent,

kernel test robot noticed the following build errors:

[auto build test ERROR on ca185770db914869ff9fe773bac5e0e5e4165b83]

url:    https://github.com/intel-lab-lkp/linux/commits/Vincent-Donnefort/ring-buffer-Zero-ring-buffer-sub-buffers/20240213-195302
base:   ca185770db914869ff9fe773bac5e0e5e4165b83
patch link:    https://lore.kernel.org/r/20240213114945.3528801-3-vdonnefort%40google.com
patch subject: [PATCH v17 2/6] ring-buffer: Introducing ring-buffer mapping functions
config: i386-buildonly-randconfig-001-20240214 (https://download.01.org/0day-ci/archive/20240214/202402140910.TFs9k0YR-lkp@intel.com/config)
compiler: clang version 17.0.6 (https://github.com/llvm/llvm-project 6009708b4367171ccdbf4b5905cb6a803753fe18)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240214/202402140910.TFs9k0YR-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202402140910.TFs9k0YR-lkp@intel.com/

All errors (new ones prefixed by >>):

>> kernel/trace/ring_buffer.c:6185:2: error: member reference type 'struct mutex' is not a pointer; did you mean to use '.'?
    6185 |         lockdep_assert_held(cpu_buffer->mapping_lock);
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/lockdep.h:267:17: note: expanded from macro 'lockdep_assert_held'
     267 |         lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
         |         ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/lockdep.h:234:52: note: expanded from macro 'lockdep_is_held'
     234 | #define lockdep_is_held(lock)           lock_is_held(&(lock)->dep_map)
         |                                                             ^
   include/linux/lockdep.h:261:32: note: expanded from macro 'lockdep_assert'
     261 |         do { WARN_ON(debug_locks && !(cond)); } while (0)
         |              ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~
   include/asm-generic/bug.h:123:25: note: expanded from macro 'WARN_ON'
     123 |         int __ret_warn_on = !!(condition);                              \
         |                                ^~~~~~~~~
>> kernel/trace/ring_buffer.c:6185:2: error: cannot take the address of an rvalue of type 'struct lockdep_map'
    6185 |         lockdep_assert_held(cpu_buffer->mapping_lock);
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/lockdep.h:267:17: note: expanded from macro 'lockdep_assert_held'
     267 |         lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
         |         ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/lockdep.h:234:45: note: expanded from macro 'lockdep_is_held'
     234 | #define lockdep_is_held(lock)           lock_is_held(&(lock)->dep_map)
         |                                                      ^
   include/linux/lockdep.h:261:32: note: expanded from macro 'lockdep_assert'
     261 |         do { WARN_ON(debug_locks && !(cond)); } while (0)
         |              ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~
   include/asm-generic/bug.h:123:25: note: expanded from macro 'WARN_ON'
     123 |         int __ret_warn_on = !!(condition);                              \
         |                                ^~~~~~~~~
   2 errors generated.


vim +6185 kernel/trace/ring_buffer.c

  6174	
  6175	/*
  6176	 * Fast-path for rb_buffer_(un)map(). Called whenever the meta-page doesn't need
  6177	 * to be set-up or torn-down.
  6178	 */
  6179	static int __rb_inc_dec_mapped(struct trace_buffer *buffer,
  6180				       struct ring_buffer_per_cpu *cpu_buffer,
  6181				       bool inc)
  6182	{
  6183		unsigned long flags;
  6184	
> 6185		lockdep_assert_held(cpu_buffer->mapping_lock);
  6186	
  6187		if (inc && cpu_buffer->mapped == UINT_MAX)
  6188			return -EBUSY;
  6189	
  6190		if (WARN_ON(!inc && cpu_buffer->mapped == 0))
  6191			return -EINVAL;
  6192	
  6193		mutex_lock(&buffer->mutex);
  6194		raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
  6195	
  6196		if (inc)
  6197			cpu_buffer->mapped++;
  6198		else
  6199			cpu_buffer->mapped--;
  6200	
  6201		raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
  6202		mutex_unlock(&buffer->mutex);
  6203	
  6204		return 0;
  6205	}
  6206	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v17 2/6] ring-buffer: Introducing ring-buffer mapping functions

[kernel test robot]

Hi Vincent,

kernel test robot noticed the following build errors:

[auto build test ERROR on ca185770db914869ff9fe773bac5e0e5e4165b83]

url:    https://github.com/intel-lab-lkp/linux/commits/Vincent-Donnefort/ring-buffer-Zero-ring-buffer-sub-buffers/20240213-195302
base:   ca185770db914869ff9fe773bac5e0e5e4165b83
patch link:    https://lore.kernel.org/r/20240213114945.3528801-3-vdonnefort%40google.com
patch subject: [PATCH v17 2/6] ring-buffer: Introducing ring-buffer mapping functions
config: x86_64-randconfig-161-20240214 (https://download.01.org/0day-ci/archive/20240214/202402141856.fVl4pCHi-lkp@intel.com/config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240214/202402141856.fVl4pCHi-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202402141856.fVl4pCHi-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from arch/x86/include/asm/bug.h:87,
                    from include/linux/bug.h:5,
                    from include/linux/jump_label.h:256,
                    from arch/x86/include/asm/string_64.h:6,
                    from arch/x86/include/asm/string.h:5,
                    from include/linux/string.h:61,
                    from include/linux/bitmap.h:12,
                    from include/linux/cpumask.h:12,
                    from include/linux/interrupt.h:8,
                    from include/linux/trace_recursion.h:5,
                    from kernel/trace/ring_buffer.c:7:
   kernel/trace/ring_buffer.c: In function '__rb_inc_dec_mapped':
>> include/linux/lockdep.h:234:52: error: invalid type argument of '->' (have 'struct mutex')
     234 | #define lockdep_is_held(lock)  lock_is_held(&(lock)->dep_map)
         |                                                    ^~
   include/asm-generic/bug.h:123:25: note: in definition of macro 'WARN_ON'
     123 |  int __ret_warn_on = !!(condition);    \
         |                         ^~~~~~~~~
   include/linux/lockdep.h:267:2: note: in expansion of macro 'lockdep_assert'
     267 |  lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
         |  ^~~~~~~~~~~~~~
   include/linux/lockdep.h:267:17: note: in expansion of macro 'lockdep_is_held'
     267 |  lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
         |                 ^~~~~~~~~~~~~~~
   kernel/trace/ring_buffer.c:6185:2: note: in expansion of macro 'lockdep_assert_held'
    6185 |  lockdep_assert_held(cpu_buffer->mapping_lock);
         |  ^~~~~~~~~~~~~~~~~~~


vim +234 include/linux/lockdep.h

f607c668577481 Peter Zijlstra 2009-07-20  233  
f8319483f57f1c Peter Zijlstra 2016-11-30 @234  #define lockdep_is_held(lock)		lock_is_held(&(lock)->dep_map)
f8319483f57f1c Peter Zijlstra 2016-11-30  235  #define lockdep_is_held_type(lock, r)	lock_is_held_type(&(lock)->dep_map, (r))
f607c668577481 Peter Zijlstra 2009-07-20  236  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH v17 3/6] tracing: Add snapshot refcount

[Steven Rostedt]

On Tue, 13 Feb 2024 11:49:42 +0000
Vincent Donnefort <vdonnefort@google.com> wrote:

> @@ -9678,7 +9739,9 @@ trace_array_create_systems(const char *name, const char *systems)
>  	raw_spin_lock_init(&tr->start_lock);
>  
>  	tr->max_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
> -
> +#ifdef CONFIG_TRCER_MAX_TRACE

Oops!

I'll fix this too.

-- Steve

> +	spinlock_init(&tr->snapshot_trigger_lock);
> +#endif
>  	tr->current_trace = &nop_trace;
>  
>  	INIT_LIST_HEAD(&tr->systems);

Re: [PATCH v17 3/6] tracing: Add snapshot refcount

[Steven Rostedt]

On Mon, 19 Feb 2024 13:17:54 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 13 Feb 2024 11:49:42 +0000
> Vincent Donnefort <vdonnefort@google.com> wrote:
> 
> > @@ -9678,7 +9739,9 @@ trace_array_create_systems(const char *name, const char *systems)
> >  	raw_spin_lock_init(&tr->start_lock);
> >  
> >  	tr->max_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
> > -
> > +#ifdef CONFIG_TRCER_MAX_TRACE  
> 
> Oops!
> 
> I'll fix this too.
> 
> 
> > +	spinlock_init(&tr->snapshot_trigger_lock);

And this too:

kernel/trace/trace.c:9245:9: error: implicit declaration of function ‘spinlock_init’; did you mean ‘spin_lock_init’? [-Werror=implicit-function-declaration]
 9245 |         spinlock_init(&tr->snapshot_trigger_lock);
      |         ^~~~~~~~~~~~~

-- Steve

> > +#endif
> >  	tr->current_trace = &nop_trace;
> >  
> >  	INIT_LIST_HEAD(&tr->systems);