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* [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1)
@ 2017-06-29 13:19 jlayton
  2017-06-29 13:19 ` [PATCH v8 01/18] fs: remove call_fsync helper function jlayton
                   ` (17 more replies)
  0 siblings, 18 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

v8:
===
- rename filemap_report_wb_err to file_check_and_advance_wb_err (per
  Darrick's suggestion)
- add a file_write_and_wait helper function (per HCH's suggestion)
- change __generic_file_fsync to use errseq_t reporting
- focus on data writeback for now, leave metadata for a follow-on set
- drop patch to always do metadata writeback in __generic_file_fsync

This is the eighth posting of the patchset to revamp the way writeback
errors are tracked and reported. Some of these patches are not new,
but I want to make it clear what I'd like to get merged into v4.13.

The main changes since the last set are a name change for the "report"
function to better indicate that it has side-effects.

Also, I've added a file_write_and_wait function to act as an analogue of
the old filemap_write_and_wait, but that uses errseq_t reporting. With
that change, it became pretty easy to convert __generic_file_fsync, so
I've gone ahead and done that. vfat now passes the simple testcase as
well.

Finally, I've dropped off a few patches here that were intended to make
it possible to report metadata writeback errors on all open fds as well.
That part is turning out to be trickier than expected, so I've decided
to just focus on data writeback here. We can pick up that piece in a
later patcheset.

If no one has major objections, I'll plan to send Linus a PR with this
pile once the merge window opens (unless someone else wants to pick it
up...Al?).

Background:
===========
The basic problem is that we have (for a very long time) tracked and
reported writeback errors based on two flags in the address_space:
AS_EIO and AS_ENOSPC. Those flags are cleared when they are checked,
so only the first caller to check them is able to consume them.

That model is quite unreliable, for several related reasons:

* only the first fsync caller on the inode will see the error. In a
  world of containerized setups, that's no longer viable. Applications
  need to know that their writes are safely stored, and they can
  currently miss seeing errors that they should be aware of when
  they're not.

* there are a lot of internal callers to filemap_fdatawait* and
  filemap_write_and_wait* that clear these errors but then never report
  them to userland in any fashion.

* Some internal callers report writeback errors, but can do so at
  non-sensical times. For instance, we might want to truncate a file,
  which triggers a pagecache flush. If that writeback fails, we might
  report that error to the truncate caller, but a subsequent fsync
  will likely not see it.

* Some internal callers try to reset the error flags after clearing
  them, but that's racy. Another task could check the flags between
  those two events.

Solution:
=========
This patchset adds a new datatype called an errseq_t that represents a
sequence of errors. It's a u32, with a field for a POSIX-flavor error
and a counter, managed with atomics. We can sample that value at a
particular point in time, and can later tell whether there have been any
errors since that point.

That allows us to provide traditional check-and-clear fsync semantics
on every open file description in a lightweight fashion. fsync callers
no longer need to coordinate between one another in order to ensure
that errors at fsync time are handled correctly.

Strategy:
=========
The aim with this pile is to do the minimum possible to support for
reliable reporting of errors on fsync, without substantially changing
the internals of the filesystems themselves.

Most of the internal calls to filemap_fdatawait are left alone, so all
of the internal error checkers are using the same error handling they
always have. The only real difference here is that we're better
reporting errors at fsync.

I think that we probably will want to eventually convert all of those
internal callers to use errseq_t based reporting, but that can be done
in an incremental fashion in follow-on patchsets.

Testing:
========
I've primarily been testing this with some new xfstests that I will post
in a separate series. These tests use dm-error fault injection to make
the underlying block device start throwing I/O errors, and then test the
how the filesystem layer reports errors after that.

Jeff Layton (18):
  fs: remove call_fsync helper function
  buffer: use mapping_set_error instead of setting the flag
  fs: check for writeback errors after syncing out buffers in
    generic_file_fsync
  buffer: set errors in mapping at the time that the error occurs
  jbd2: don't clear and reset errors after waiting on writeback
  mm: clear AS_EIO/AS_ENOSPC when writeback initiation fails
  mm: don't TestClearPageError in __filemap_fdatawait_range
  mm: clean up error handling in write_one_page
  lib: add errseq_t type and infrastructure for handling it
  fs: new infrastructure for writeback error handling and reporting
  mm: set both AS_EIO/AS_ENOSPC and errseq_t in mapping_set_error
  Documentation: flesh out the section in vfs.txt on storing and
    reporting writeback errors
  dax: set errors in mapping when writeback fails
  block: convert to errseq_t based writeback error tracking
  fs: convert __generic_file_fsync to use errseq_t based reporting
  ext4: use errseq_t based error handling for reporting data writeback
    errors
  xfs: minimal conversion to errseq_t writeback error reporting
  btrfs: minimal conversion to errseq_t writeback error reporting on
    fsync

 Documentation/filesystems/vfs.txt |  43 +++++++-
 MAINTAINERS                       |   6 ++
 drivers/dax/device.c              |   1 +
 fs/block_dev.c                    |   3 +-
 fs/btrfs/file.c                   |   7 +-
 fs/buffer.c                       |  20 ++--
 fs/dax.c                          |   4 +-
 fs/ext2/file.c                    |   5 +-
 fs/ext4/fsync.c                   |  13 ++-
 fs/file_table.c                   |   1 +
 fs/gfs2/lops.c                    |   2 +-
 fs/jbd2/commit.c                  |  16 +--
 fs/libfs.c                        |   6 +-
 fs/open.c                         |   3 +
 fs/sync.c                         |   2 +-
 fs/xfs/xfs_file.c                 |   2 +-
 include/linux/buffer_head.h       |   1 +
 include/linux/errseq.h            |  19 ++++
 include/linux/fs.h                |  68 +++++++++++--
 include/linux/pagemap.h           |  31 ++++--
 include/trace/events/filemap.h    |  57 +++++++++++
 ipc/shm.c                         |   2 +-
 lib/Makefile                      |   2 +-
 lib/errseq.c                      | 208 ++++++++++++++++++++++++++++++++++++++
 mm/filemap.c                      | 128 +++++++++++++++++++----
 mm/page-writeback.c               |  13 ++-
 26 files changed, 584 insertions(+), 79 deletions(-)
 create mode 100644 include/linux/errseq.h
 create mode 100644 lib/errseq.c

-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 01/18] fs: remove call_fsync helper function
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 13:19 ` [PATCH v8 02/18] buffer: use mapping_set_error instead of setting the flag jlayton
                   ` (16 subsequent siblings)
  17 siblings, 0 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/sync.c          | 2 +-
 include/linux/fs.h | 6 ------
 ipc/shm.c          | 2 +-
 3 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/fs/sync.c b/fs/sync.c
index 11ba023434b1..2a54c1f22035 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -192,7 +192,7 @@ int vfs_fsync_range(struct file *file, loff_t start, loff_t end, int datasync)
 		spin_unlock(&inode->i_lock);
 		mark_inode_dirty_sync(inode);
 	}
-	return call_fsync(file, start, end, datasync);
+	return file->f_op->fsync(file, start, end, datasync);
 }
 EXPORT_SYMBOL(vfs_fsync_range);
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 1e53cd281437..4ff4498297fa 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1739,12 +1739,6 @@ static inline int call_mmap(struct file *file, struct vm_area_struct *vma)
 	return file->f_op->mmap(file, vma);
 }
 
-static inline int call_fsync(struct file *file, loff_t start, loff_t end,
-			     int datasync)
-{
-	return file->f_op->fsync(file, start, end, datasync);
-}
-
 ssize_t rw_copy_check_uvector(int type, const struct iovec __user * uvector,
 			      unsigned long nr_segs, unsigned long fast_segs,
 			      struct iovec *fast_pointer,
diff --git a/ipc/shm.c b/ipc/shm.c
index 34c4344e8d4b..f45c7959b264 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -452,7 +452,7 @@ static int shm_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 
 	if (!sfd->file->f_op->fsync)
 		return -EINVAL;
-	return call_fsync(sfd->file, start, end, datasync);
+	return sfd->file->f_op->fsync(sfd->file, start, end, datasync);
 }
 
 static long shm_fallocate(struct file *file, int mode, loff_t offset,
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 02/18] buffer: use mapping_set_error instead of setting the flag
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
  2017-06-29 13:19 ` [PATCH v8 01/18] fs: remove call_fsync helper function jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 13:19 ` [PATCH v8 03/18] fs: check for writeback errors after syncing out buffers in generic_file_fsync jlayton
                   ` (15 subsequent siblings)
  17 siblings, 0 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 161be58c5cb0..4be8b914a222 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -482,7 +482,7 @@ static void __remove_assoc_queue(struct buffer_head *bh)
 	list_del_init(&bh->b_assoc_buffers);
 	WARN_ON(!bh->b_assoc_map);
 	if (buffer_write_io_error(bh))
-		set_bit(AS_EIO, &bh->b_assoc_map->flags);
+		mapping_set_error(bh->b_assoc_map, -EIO);
 	bh->b_assoc_map = NULL;
 }
 
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 03/18] fs: check for writeback errors after syncing out buffers in generic_file_fsync
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
  2017-06-29 13:19 ` [PATCH v8 01/18] fs: remove call_fsync helper function jlayton
  2017-06-29 13:19 ` [PATCH v8 02/18] buffer: use mapping_set_error instead of setting the flag jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 14:19   ` Christoph Hellwig
  2017-06-29 13:19 ` [PATCH v8 04/18] buffer: set errors in mapping at the time that the error occurs jlayton
                   ` (14 subsequent siblings)
  17 siblings, 1 reply; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

ext2 currently does a test+clear of the AS_EIO flag, which is
is problematic for some coming changes.

What we really need to do instead is call filemap_check_errors
in __generic_file_fsync after syncing out the buffers. That
will be sufficient for this case, and help other callers detect
these errors properly as well.

With that, we don't need to twiddle it in ext2.

Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
---
 fs/ext2/file.c | 5 +----
 fs/libfs.c     | 3 ++-
 2 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/fs/ext2/file.c b/fs/ext2/file.c
index b21891a6bfca..d34d32bdc944 100644
--- a/fs/ext2/file.c
+++ b/fs/ext2/file.c
@@ -174,15 +174,12 @@ int ext2_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 {
 	int ret;
 	struct super_block *sb = file->f_mapping->host->i_sb;
-	struct address_space *mapping = sb->s_bdev->bd_inode->i_mapping;
 
 	ret = generic_file_fsync(file, start, end, datasync);
-	if (ret == -EIO || test_and_clear_bit(AS_EIO, &mapping->flags)) {
+	if (ret == -EIO)
 		/* We don't really know where the IO error happened... */
 		ext2_error(sb, __func__,
 			   "detected IO error when writing metadata buffers");
-		ret = -EIO;
-	}
 	return ret;
 }
 
diff --git a/fs/libfs.c b/fs/libfs.c
index a04395334bb1..1dec90819366 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -991,7 +991,8 @@ int __generic_file_fsync(struct file *file, loff_t start, loff_t end,
 
 out:
 	inode_unlock(inode);
-	return ret;
+	err = filemap_check_errors(inode->i_mapping);
+	return ret ? ret : err;
 }
 EXPORT_SYMBOL(__generic_file_fsync);
 
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 04/18] buffer: set errors in mapping at the time that the error occurs
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (2 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 03/18] fs: check for writeback errors after syncing out buffers in generic_file_fsync jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 13:19 ` [PATCH v8 05/18] jbd2: don't clear and reset errors after waiting on writeback jlayton
                   ` (13 subsequent siblings)
  17 siblings, 0 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

I noticed on xfs that I could still sometimes get back an error on fsync
on a fd that was opened after the error condition had been cleared.

The problem is that the buffer code sets the write_io_error flag and
then later checks that flag to set the error in the mapping. That flag
perisists for quite a while however. If the file is later opened with
O_TRUNC, the buffers will then be invalidated and the mapping's error
set such that a subsequent fsync will return error. I think this is
incorrect, as there was no writeback between the open and fsync.

Add a new mark_buffer_write_io_error operation that sets the flag and
the error in the mapping at the same time. Replace all calls to
set_buffer_write_io_error with mark_buffer_write_io_error, and remove
the places that check this flag in order to set the error in the
mapping.

This sets the error in the mapping earlier, at the time that it's first
detected.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
---
 fs/buffer.c                 | 20 +++++++++++++-------
 fs/gfs2/lops.c              |  2 +-
 include/linux/buffer_head.h |  1 +
 3 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 4be8b914a222..b946149e8214 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -178,7 +178,7 @@ void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 		set_buffer_uptodate(bh);
 	} else {
 		buffer_io_error(bh, ", lost sync page write");
-		set_buffer_write_io_error(bh);
+		mark_buffer_write_io_error(bh);
 		clear_buffer_uptodate(bh);
 	}
 	unlock_buffer(bh);
@@ -352,8 +352,7 @@ void end_buffer_async_write(struct buffer_head *bh, int uptodate)
 		set_buffer_uptodate(bh);
 	} else {
 		buffer_io_error(bh, ", lost async page write");
-		mapping_set_error(page->mapping, -EIO);
-		set_buffer_write_io_error(bh);
+		mark_buffer_write_io_error(bh);
 		clear_buffer_uptodate(bh);
 		SetPageError(page);
 	}
@@ -481,8 +480,6 @@ static void __remove_assoc_queue(struct buffer_head *bh)
 {
 	list_del_init(&bh->b_assoc_buffers);
 	WARN_ON(!bh->b_assoc_map);
-	if (buffer_write_io_error(bh))
-		mapping_set_error(bh->b_assoc_map, -EIO);
 	bh->b_assoc_map = NULL;
 }
 
@@ -1181,6 +1178,17 @@ void mark_buffer_dirty(struct buffer_head *bh)
 }
 EXPORT_SYMBOL(mark_buffer_dirty);
 
+void mark_buffer_write_io_error(struct buffer_head *bh)
+{
+	set_buffer_write_io_error(bh);
+	/* FIXME: do we need to set this in both places? */
+	if (bh->b_page && bh->b_page->mapping)
+		mapping_set_error(bh->b_page->mapping, -EIO);
+	if (bh->b_assoc_map)
+		mapping_set_error(bh->b_assoc_map, -EIO);
+}
+EXPORT_SYMBOL(mark_buffer_write_io_error);
+
 /*
  * Decrement a buffer_head's reference count.  If all buffers against a page
  * have zero reference count, are clean and unlocked, and if the page is clean
@@ -3279,8 +3287,6 @@ drop_buffers(struct page *page, struct buffer_head **buffers_to_free)
 
 	bh = head;
 	do {
-		if (buffer_write_io_error(bh) && page->mapping)
-			mapping_set_error(page->mapping, -EIO);
 		if (buffer_busy(bh))
 			goto failed;
 		bh = bh->b_this_page;
diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index b1f9144b42c7..cd7857ab1a6a 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -182,7 +182,7 @@ static void gfs2_end_log_write_bh(struct gfs2_sbd *sdp, struct bio_vec *bvec,
 		bh = bh->b_this_page;
 	do {
 		if (error)
-			set_buffer_write_io_error(bh);
+			mark_buffer_write_io_error(bh);
 		unlock_buffer(bh);
 		next = bh->b_this_page;
 		size -= bh->b_size;
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index bd029e52ef5e..e0abeba3ced7 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -149,6 +149,7 @@ void buffer_check_dirty_writeback(struct page *page,
  */
 
 void mark_buffer_dirty(struct buffer_head *bh);
+void mark_buffer_write_io_error(struct buffer_head *bh);
 void init_buffer(struct buffer_head *, bh_end_io_t *, void *);
 void touch_buffer(struct buffer_head *bh);
 void set_bh_page(struct buffer_head *bh,
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 05/18] jbd2: don't clear and reset errors after waiting on writeback
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (3 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 04/18] buffer: set errors in mapping at the time that the error occurs jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 13:19 ` [PATCH v8 06/18] mm: clear AS_EIO/AS_ENOSPC when writeback initiation fails jlayton
                   ` (12 subsequent siblings)
  17 siblings, 0 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

Resetting this flag is almost certainly racy, and will be problematic
with some coming changes.

Make filemap_fdatawait_keep_errors return int, but not clear the flag(s).
Have jbd2 call it instead of filemap_fdatawait and don't attempt to
re-set the error flag if it fails.

Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/jbd2/commit.c   | 16 ++++------------
 include/linux/fs.h |  2 +-
 mm/filemap.c       | 16 ++++++++++++++--
 3 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index b6b194ec1b4f..3c1c31321d9b 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -263,18 +263,10 @@ static int journal_finish_inode_data_buffers(journal_t *journal,
 			continue;
 		jinode->i_flags |= JI_COMMIT_RUNNING;
 		spin_unlock(&journal->j_list_lock);
-		err = filemap_fdatawait(jinode->i_vfs_inode->i_mapping);
-		if (err) {
-			/*
-			 * Because AS_EIO is cleared by
-			 * filemap_fdatawait_range(), set it again so
-			 * that user process can get -EIO from fsync().
-			 */
-			mapping_set_error(jinode->i_vfs_inode->i_mapping, -EIO);
-
-			if (!ret)
-				ret = err;
-		}
+		err = filemap_fdatawait_keep_errors(
+				jinode->i_vfs_inode->i_mapping);
+		if (!ret)
+			ret = err;
 		spin_lock(&journal->j_list_lock);
 		jinode->i_flags &= ~JI_COMMIT_RUNNING;
 		smp_mb();
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 4ff4498297fa..74872c0f1c07 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2508,7 +2508,7 @@ extern int write_inode_now(struct inode *, int);
 extern int filemap_fdatawrite(struct address_space *);
 extern int filemap_flush(struct address_space *);
 extern int filemap_fdatawait(struct address_space *);
-extern void filemap_fdatawait_keep_errors(struct address_space *);
+extern int filemap_fdatawait_keep_errors(struct address_space *mapping);
 extern int filemap_fdatawait_range(struct address_space *, loff_t lstart,
 				   loff_t lend);
 extern int filemap_write_and_wait(struct address_space *mapping);
diff --git a/mm/filemap.c b/mm/filemap.c
index 6f1be573a5e6..e5711b2728f4 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -309,6 +309,16 @@ int filemap_check_errors(struct address_space *mapping)
 }
 EXPORT_SYMBOL(filemap_check_errors);
 
+static int filemap_check_and_keep_errors(struct address_space *mapping)
+{
+	/* Check for outstanding write errors */
+	if (test_bit(AS_EIO, &mapping->flags))
+		return -EIO;
+	if (test_bit(AS_ENOSPC, &mapping->flags))
+		return -ENOSPC;
+	return 0;
+}
+
 /**
  * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
  * @mapping:	address space structure to write
@@ -453,15 +463,17 @@ EXPORT_SYMBOL(filemap_fdatawait_range);
  * call sites are system-wide / filesystem-wide data flushers: e.g. sync(2),
  * fsfreeze(8)
  */
-void filemap_fdatawait_keep_errors(struct address_space *mapping)
+int filemap_fdatawait_keep_errors(struct address_space *mapping)
 {
 	loff_t i_size = i_size_read(mapping->host);
 
 	if (i_size == 0)
-		return;
+		return 0;
 
 	__filemap_fdatawait_range(mapping, 0, i_size - 1);
+	return filemap_check_and_keep_errors(mapping);
 }
+EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
 
 /**
  * filemap_fdatawait - wait for all under-writeback pages to complete
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 06/18] mm: clear AS_EIO/AS_ENOSPC when writeback initiation fails
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (4 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 05/18] jbd2: don't clear and reset errors after waiting on writeback jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 13:19 ` [PATCH v8 07/18] mm: don't TestClearPageError in __filemap_fdatawait_range jlayton
                   ` (11 subsequent siblings)
  17 siblings, 0 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

filemap_write_and_wait{_range} will return an error if writeback
initiation fails, but won't clear errors in the address_space. This is
particularly problematic on DAX, as it's effectively synchronous. Ensure
that we clear the AS_EIO/AS_ENOSPC flags when filemap_fdatawrite returns
an error.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 mm/filemap.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c
index e5711b2728f4..49bc9720fb00 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -515,6 +515,9 @@ int filemap_write_and_wait(struct address_space *mapping)
 			int err2 = filemap_fdatawait(mapping);
 			if (!err)
 				err = err2;
+		} else {
+			/* Clear any previously stored errors */
+			filemap_check_errors(mapping);
 		}
 	} else {
 		err = filemap_check_errors(mapping);
@@ -549,6 +552,9 @@ int filemap_write_and_wait_range(struct address_space *mapping,
 						lstart, lend);
 			if (!err)
 				err = err2;
+		} else {
+			/* Clear any previously stored errors */
+			filemap_check_errors(mapping);
 		}
 	} else {
 		err = filemap_check_errors(mapping);
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 07/18] mm: don't TestClearPageError in __filemap_fdatawait_range
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (5 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 06/18] mm: clear AS_EIO/AS_ENOSPC when writeback initiation fails jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 13:19 ` [PATCH v8 08/18] mm: clean up error handling in write_one_page jlayton
                   ` (10 subsequent siblings)
  17 siblings, 0 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

The -EIO returned here can end up overriding whatever error is marked in
the address space, and be returned at fsync time, even when there is a
more appropriate error stored in the mapping.

Read errors are also sometimes tracked on a per-page level using
PG_error. Suppose we have a read error on a page, and then that page is
subsequently dirtied by overwriting the whole page. Writeback doesn't
clear PG_error, so we can then end up successfully writing back that
page and still return -EIO on fsync.

Worse yet, PG_error is cleared during a sync() syscall, but the -EIO
return from that is silently discarded. Any subsystem that is relying on
PG_error to report errors during fsync can easily lose writeback errors
due to this. All you need is a stray sync() call to wait for writeback
to complete and you've lost the error.

Since the handling of the PG_error flag is somewhat inconsistent across
subsystems, let's just rely on marking the address space when there are
writeback errors. Change the TestClearPageError call to ClearPageError,
and make __filemap_fdatawait_range a void return function.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 mm/filemap.c | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 49bc9720fb00..eb99b5f23c61 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -386,17 +386,16 @@ int filemap_flush(struct address_space *mapping)
 }
 EXPORT_SYMBOL(filemap_flush);
 
-static int __filemap_fdatawait_range(struct address_space *mapping,
+static void __filemap_fdatawait_range(struct address_space *mapping,
 				     loff_t start_byte, loff_t end_byte)
 {
 	pgoff_t index = start_byte >> PAGE_SHIFT;
 	pgoff_t end = end_byte >> PAGE_SHIFT;
 	struct pagevec pvec;
 	int nr_pages;
-	int ret = 0;
 
 	if (end_byte < start_byte)
-		goto out;
+		return;
 
 	pagevec_init(&pvec, 0);
 	while ((index <= end) &&
@@ -413,14 +412,11 @@ static int __filemap_fdatawait_range(struct address_space *mapping,
 				continue;
 
 			wait_on_page_writeback(page);
-			if (TestClearPageError(page))
-				ret = -EIO;
+			ClearPageError(page);
 		}
 		pagevec_release(&pvec);
 		cond_resched();
 	}
-out:
-	return ret;
 }
 
 /**
@@ -440,14 +436,8 @@ static int __filemap_fdatawait_range(struct address_space *mapping,
 int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
 			    loff_t end_byte)
 {
-	int ret, ret2;
-
-	ret = __filemap_fdatawait_range(mapping, start_byte, end_byte);
-	ret2 = filemap_check_errors(mapping);
-	if (!ret)
-		ret = ret2;
-
-	return ret;
+	__filemap_fdatawait_range(mapping, start_byte, end_byte);
+	return filemap_check_errors(mapping);
 }
 EXPORT_SYMBOL(filemap_fdatawait_range);
 
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 08/18] mm: clean up error handling in write_one_page
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (6 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 07/18] mm: don't TestClearPageError in __filemap_fdatawait_range jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 13:19 ` [PATCH v8 09/18] lib: add errseq_t type and infrastructure for handling it jlayton
                   ` (9 subsequent siblings)
  17 siblings, 0 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

Don't try to check PageError since that's potentially racy and not
necessarily going to be set after writepage errors out.

Instead, check the mapping for an error after writepage returns.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 mm/page-writeback.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b901fe52b153..db30ce0b7d80 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2371,9 +2371,8 @@ int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
  *
  * The page must be locked by the caller and will be unlocked upon return.
  *
- * write_one_page() returns a negative error code if I/O failed. Note that
- * the address_space is not marked for error. The caller must do this if
- * needed.
+ * Note that the mapping's AS_EIO/AS_ENOSPC flags will be cleared when this
+ * function returns.
  */
 int write_one_page(struct page *page)
 {
@@ -2391,15 +2390,15 @@ int write_one_page(struct page *page)
 	if (clear_page_dirty_for_io(page)) {
 		get_page(page);
 		ret = mapping->a_ops->writepage(page, &wbc);
-		if (ret == 0) {
+		if (ret == 0)
 			wait_on_page_writeback(page);
-			if (PageError(page))
-				ret = -EIO;
-		}
 		put_page(page);
 	} else {
 		unlock_page(page);
 	}
+
+	if (!ret)
+		ret = filemap_check_errors(mapping);
 	return ret;
 }
 EXPORT_SYMBOL(write_one_page);
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 09/18] lib: add errseq_t type and infrastructure for handling it
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (7 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 08/18] mm: clean up error handling in write_one_page jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 13:19 ` [PATCH v8 10/18] fs: new infrastructure for writeback error handling and reporting jlayton
                   ` (8 subsequent siblings)
  17 siblings, 0 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

An errseq_t is a way of recording errors in one place, and allowing any
number of "subscribers" to tell whether an error has been set again
since a previous time.

It's implemented as an unsigned 32-bit value that is managed with atomic
operations. The low order bits are designated to hold an error code
(max size of MAX_ERRNO). The upper bits are used as a counter.

The API works with consumers sampling an errseq_t value at a particular
point in time. Later, that value can be used to tell whether new errors
have been set since that time.

Note that there is a 1 in 512k risk of collisions here if new errors
are being recorded frequently, since we have so few bits to use as a
counter. To mitigate this, one bit is used as a flag to tell whether the
value has been sampled since a new value was recorded. That allows
us to avoid bumping the counter if no one has sampled it since it
was last bumped.

Later patches will build on this infrastructure to change how writeback
errors are tracked in the kernel.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: NeilBrown <neilb@suse.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 MAINTAINERS            |   6 ++
 include/linux/errseq.h |  19 +++++
 lib/Makefile           |   2 +-
 lib/errseq.c           | 208 +++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 234 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/errseq.h
 create mode 100644 lib/errseq.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 9e984645c4b0..c2465dc21946 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4999,6 +4999,12 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/kristoffer/linux-hpc.git
 F:	drivers/video/fbdev/s1d13xxxfb.c
 F:	include/video/s1d13xxxfb.h
 
+ERRSEQ ERROR TRACKING INFRASTRUCTURE
+M:	Jeff Layton <jlayton@poochiereds.net>
+S:	Maintained
+F:	lib/errseq.c
+F:	include/linux/errseq.h
+
 ET131X NETWORK DRIVER
 M:	Mark Einon <mark.einon@gmail.com>
 S:	Odd Fixes
diff --git a/include/linux/errseq.h b/include/linux/errseq.h
new file mode 100644
index 000000000000..9e0d444ac88d
--- /dev/null
+++ b/include/linux/errseq.h
@@ -0,0 +1,19 @@
+#ifndef _LINUX_ERRSEQ_H
+#define _LINUX_ERRSEQ_H
+
+/* See lib/errseq.c for more info */
+
+typedef u32	errseq_t;
+
+errseq_t __errseq_set(errseq_t *eseq, int err);
+static inline void errseq_set(errseq_t *eseq, int err)
+{
+	/* Optimize for the common case of no error */
+	if (unlikely(err))
+		__errseq_set(eseq, err);
+}
+
+errseq_t errseq_sample(errseq_t *eseq);
+int errseq_check(errseq_t *eseq, errseq_t since);
+int errseq_check_and_advance(errseq_t *eseq, errseq_t *since);
+#endif
diff --git a/lib/Makefile b/lib/Makefile
index 0166fbc0fa81..519782d9ca3f 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -41,7 +41,7 @@ obj-y += bcd.o div64.o sort.o parser.o debug_locks.o random32.o \
 	 gcd.o lcm.o list_sort.o uuid.o flex_array.o iov_iter.o clz_ctz.o \
 	 bsearch.o find_bit.o llist.o memweight.o kfifo.o \
 	 percpu-refcount.o percpu_ida.o rhashtable.o reciprocal_div.o \
-	 once.o refcount.o usercopy.o
+	 once.o refcount.o usercopy.o errseq.o
 obj-y += string_helpers.o
 obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
 obj-y += hexdump.o
diff --git a/lib/errseq.c b/lib/errseq.c
new file mode 100644
index 000000000000..841fa24e6e00
--- /dev/null
+++ b/lib/errseq.c
@@ -0,0 +1,208 @@
+#include <linux/err.h>
+#include <linux/bug.h>
+#include <linux/atomic.h>
+#include <linux/errseq.h>
+
+/*
+ * An errseq_t is a way of recording errors in one place, and allowing any
+ * number of "subscribers" to tell whether it has changed since a previous
+ * point where it was sampled.
+ *
+ * It's implemented as an unsigned 32-bit value. The low order bits are
+ * designated to hold an error code (between 0 and -MAX_ERRNO). The upper bits
+ * are used as a counter. This is done with atomics instead of locking so that
+ * these functions can be called from any context.
+ *
+ * The general idea is for consumers to sample an errseq_t value. That value
+ * can later be used to tell whether any new errors have occurred since that
+ * sampling was done.
+ *
+ * Note that there is a risk of collisions if new errors are being recorded
+ * frequently, since we have so few bits to use as a counter.
+ *
+ * To mitigate this, one bit is used as a flag to tell whether the value has
+ * been sampled since a new value was recorded. That allows us to avoid bumping
+ * the counter if no one has sampled it since the last time an error was
+ * recorded.
+ *
+ * A new errseq_t should always be zeroed out.  A errseq_t value of all zeroes
+ * is the special (but common) case where there has never been an error. An all
+ * zero value thus serves as the "epoch" if one wishes to know whether there
+ * has ever been an error set since it was first initialized.
+ */
+
+/* The low bits are designated for error code (max of MAX_ERRNO) */
+#define ERRSEQ_SHIFT		ilog2(MAX_ERRNO + 1)
+
+/* This bit is used as a flag to indicate whether the value has been seen */
+#define ERRSEQ_SEEN		(1 << ERRSEQ_SHIFT)
+
+/* The lowest bit of the counter */
+#define ERRSEQ_CTR_INC		(1 << (ERRSEQ_SHIFT + 1))
+
+/**
+ * __errseq_set - set a errseq_t for later reporting
+ * @eseq: errseq_t field that should be set
+ * @err: error to set
+ *
+ * This function sets the error in *eseq, and increments the sequence counter
+ * if the last sequence was sampled at some point in the past.
+ *
+ * Any error set will always overwrite an existing error.
+ *
+ * Most callers will want to use the errseq_set inline wrapper to efficiently
+ * handle the common case where err is 0.
+ *
+ * We do return an errseq_t here, primarily for debugging purposes. The return
+ * value should not be used as a previously sampled value in later calls as it
+ * will not have the SEEN flag set.
+ */
+errseq_t __errseq_set(errseq_t *eseq, int err)
+{
+	errseq_t cur, old;
+
+	/* MAX_ERRNO must be able to serve as a mask */
+	BUILD_BUG_ON_NOT_POWER_OF_2(MAX_ERRNO + 1);
+
+	/*
+	 * Ensure the error code actually fits where we want it to go. If it
+	 * doesn't then just throw a warning and don't record anything. We
+	 * also don't accept zero here as that would effectively clear a
+	 * previous error.
+	 */
+	old = READ_ONCE(*eseq);
+
+	if (WARN(unlikely(err == 0 || (unsigned int)-err > MAX_ERRNO),
+				"err = %d\n", err))
+		return old;
+
+	for (;;) {
+		errseq_t new;
+
+		/* Clear out error bits and set new error */
+		new = (old & ~(MAX_ERRNO|ERRSEQ_SEEN)) | -err;
+
+		/* Only increment if someone has looked at it */
+		if (old & ERRSEQ_SEEN)
+			new += ERRSEQ_CTR_INC;
+
+		/* If there would be no change, then call it done */
+		if (new == old) {
+			cur = new;
+			break;
+		}
+
+		/* Try to swap the new value into place */
+		cur = cmpxchg(eseq, old, new);
+
+		/*
+		 * Call it success if we did the swap or someone else beat us
+		 * to it for the same value.
+		 */
+		if (likely(cur == old || cur == new))
+			break;
+
+		/* Raced with an update, try again */
+		old = cur;
+	}
+	return cur;
+}
+EXPORT_SYMBOL(__errseq_set);
+
+/**
+ * errseq_sample - grab current errseq_t value
+ * @eseq: pointer to errseq_t to be sampled
+ *
+ * This function allows callers to sample an errseq_t value, marking it as
+ * "seen" if required.
+ */
+errseq_t errseq_sample(errseq_t *eseq)
+{
+	errseq_t old = READ_ONCE(*eseq);
+	errseq_t new = old;
+
+	/*
+	 * For the common case of no errors ever having been set, we can skip
+	 * marking the SEEN bit. Once an error has been set, the value will
+	 * never go back to zero.
+	 */
+	if (old != 0) {
+		new |= ERRSEQ_SEEN;
+		if (old != new)
+			cmpxchg(eseq, old, new);
+	}
+	return new;
+}
+EXPORT_SYMBOL(errseq_sample);
+
+/**
+ * errseq_check - has an error occurred since a particular sample point?
+ * @eseq: pointer to errseq_t value to be checked
+ * @since: previously-sampled errseq_t from which to check
+ *
+ * Grab the value that eseq points to, and see if it has changed "since"
+ * the given value was sampled. The "since" value is not advanced, so there
+ * is no need to mark the value as seen.
+ *
+ * Returns the latest error set in the errseq_t or 0 if it hasn't changed.
+ */
+int errseq_check(errseq_t *eseq, errseq_t since)
+{
+	errseq_t cur = READ_ONCE(*eseq);
+
+	if (likely(cur == since))
+		return 0;
+	return -(cur & MAX_ERRNO);
+}
+EXPORT_SYMBOL(errseq_check);
+
+/**
+ * errseq_check_and_advance - check an errseq_t and advance to current value
+ * @eseq: pointer to value being checked and reported
+ * @since: pointer to previously-sampled errseq_t to check against and advance
+ *
+ * Grab the eseq value, and see whether it matches the value that "since"
+ * points to. If it does, then just return 0.
+ *
+ * If it doesn't, then the value has changed. Set the "seen" flag, and try to
+ * swap it into place as the new eseq value. Then, set that value as the new
+ * "since" value, and return whatever the error portion is set to.
+ *
+ * Note that no locking is provided here for concurrent updates to the "since"
+ * value. The caller must provide that if necessary. Because of this, callers
+ * may want to do a lockless errseq_check before taking the lock and calling
+ * this.
+ */
+int errseq_check_and_advance(errseq_t *eseq, errseq_t *since)
+{
+	int err = 0;
+	errseq_t old, new;
+
+	/*
+	 * Most callers will want to use the inline wrapper to check this,
+	 * so that the common case of no error is handled without needing
+	 * to take the lock that protects the "since" value.
+	 */
+	old = READ_ONCE(*eseq);
+	if (old != *since) {
+		/*
+		 * Set the flag and try to swap it into place if it has
+		 * changed.
+		 *
+		 * We don't care about the outcome of the swap here. If the
+		 * swap doesn't occur, then it has either been updated by a
+		 * writer who is altering the value in some way (updating
+		 * counter or resetting the error), or another reader who is
+		 * just setting the "seen" flag. Either outcome is OK, and we
+		 * can advance "since" and return an error based on what we
+		 * have.
+		 */
+		new = old | ERRSEQ_SEEN;
+		if (new != old)
+			cmpxchg(eseq, old, new);
+		*since = new;
+		err = -(new & MAX_ERRNO);
+	}
+	return err;
+}
+EXPORT_SYMBOL(errseq_check_and_advance);
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 10/18] fs: new infrastructure for writeback error handling and reporting
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (8 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 09/18] lib: add errseq_t type and infrastructure for handling it jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 13:45   ` Jeff Layton
  2017-06-29 17:52   ` Jeff Layton
  2017-06-29 13:19 ` [PATCH v8 11/18] mm: set both AS_EIO/AS_ENOSPC and errseq_t in mapping_set_error jlayton
                   ` (7 subsequent siblings)
  17 siblings, 2 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

Most filesystems currently use mapping_set_error and
filemap_check_errors for setting and reporting/clearing writeback errors
at the mapping level. filemap_check_errors is indirectly called from
most of the filemap_fdatawait_* functions and from
filemap_write_and_wait*. These functions are called from all sorts of
contexts to wait on writeback to finish -- e.g. mostly in fsync, but
also in truncate calls, getattr, etc.

The non-fsync callers are problematic. We should be reporting writeback
errors during fsync, but many places spread over the tree clear out
errors before they can be properly reported, or report errors at
nonsensical times.

If I get -EIO on a stat() call, there is no reason for me to assume that
it is because some previous writeback failed. The fact that it also
clears out the error such that a subsequent fsync returns 0 is a bug,
and a nasty one since that's potentially silent data corruption.

This patch adds a small bit of new infrastructure for setting and
reporting errors during address_space writeback. While the above was my
original impetus for adding this, I think it's also the case that
current fsync semantics are just problematic for userland. Most
applications that call fsync do so to ensure that the data they wrote
has hit the backing store.

In the case where there are multiple writers to the file at the same
time, this is really hard to determine. The first one to call fsync will
see any stored error, and the rest get back 0. The processes with open
fds may not be associated with one another in any way. They could even
be in different containers, so ensuring coordination between all fsync
callers is not really an option.

One way to remedy this would be to track what file descriptor was used
to dirty the file, but that's rather cumbersome and would likely be
slow. However, there is a simpler way to improve the semantics here
without incurring too much overhead.

This set adds an errseq_t to struct address_space, and a corresponding
one is added to struct file. Writeback errors are recorded in the
mapping's errseq_t, and the one in struct file is used as the "since"
value.

This changes the semantics of the Linux fsync implementation such that
applications can now use it to determine whether there were any
writeback errors since fsync(fd) was last called (or since the file was
opened in the case of fsync having never been called).

Note that those writeback errors may have occurred when writing data
that was dirtied via an entirely different fd, but that's the case now
with the current mapping_set_error/filemap_check_error infrastructure.
This will at least prevent you from getting a false report of success.

The new behavior is still consistent with the POSIX spec, and is more
reliable for application developers. This patch just adds some basic
infrastructure for doing this, and ensures that the f_wb_err "cursor"
is properly set when a file is opened. Later patches will change the
existing code to use this new infrastructure for reporting errors at
fsync time.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 drivers/dax/device.c           |  1 +
 fs/block_dev.c                 |  1 +
 fs/file_table.c                |  1 +
 fs/open.c                      |  3 ++
 include/linux/fs.h             | 60 ++++++++++++++++++++++++++++-
 include/trace/events/filemap.h | 57 ++++++++++++++++++++++++++++
 mm/filemap.c                   | 86 ++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 208 insertions(+), 1 deletion(-)

diff --git a/drivers/dax/device.c b/drivers/dax/device.c
index 006e657dfcb9..12943d19bfc4 100644
--- a/drivers/dax/device.c
+++ b/drivers/dax/device.c
@@ -499,6 +499,7 @@ static int dax_open(struct inode *inode, struct file *filp)
 	inode->i_mapping = __dax_inode->i_mapping;
 	inode->i_mapping->host = __dax_inode;
 	filp->f_mapping = inode->i_mapping;
+	filp->f_wb_err = filemap_sample_wb_err(filp->f_mapping);
 	filp->private_data = dev_dax;
 	inode->i_flags = S_DAX;
 
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 519599dddd36..4d62fe771587 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1743,6 +1743,7 @@ static int blkdev_open(struct inode * inode, struct file * filp)
 		return -ENOMEM;
 
 	filp->f_mapping = bdev->bd_inode->i_mapping;
+	filp->f_wb_err = filemap_sample_wb_err(filp->f_mapping);
 
 	return blkdev_get(bdev, filp->f_mode, filp);
 }
diff --git a/fs/file_table.c b/fs/file_table.c
index 954d510b765a..72e861a35a7f 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -168,6 +168,7 @@ struct file *alloc_file(const struct path *path, fmode_t mode,
 	file->f_path = *path;
 	file->f_inode = path->dentry->d_inode;
 	file->f_mapping = path->dentry->d_inode->i_mapping;
+	file->f_wb_err = filemap_sample_wb_err(file->f_mapping);
 	if ((mode & FMODE_READ) &&
 	     likely(fop->read || fop->read_iter))
 		mode |= FMODE_CAN_READ;
diff --git a/fs/open.c b/fs/open.c
index cd0c5be8d012..280d4a963791 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -707,6 +707,9 @@ static int do_dentry_open(struct file *f,
 	f->f_inode = inode;
 	f->f_mapping = inode->i_mapping;
 
+	/* Ensure that we skip any errors that predate opening of the file */
+	f->f_wb_err = filemap_sample_wb_err(f->f_mapping);
+
 	if (unlikely(f->f_flags & O_PATH)) {
 		f->f_mode = FMODE_PATH;
 		f->f_op = &empty_fops;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 74872c0f1c07..b524fd442057 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -30,7 +30,7 @@
 #include <linux/percpu-rwsem.h>
 #include <linux/workqueue.h>
 #include <linux/delayed_call.h>
-
+#include <linux/errseq.h>
 #include <asm/byteorder.h>
 #include <uapi/linux/fs.h>
 
@@ -392,6 +392,7 @@ struct address_space {
 	gfp_t			gfp_mask;	/* implicit gfp mask for allocations */
 	struct list_head	private_list;	/* ditto */
 	void			*private_data;	/* ditto */
+	errseq_t		wb_err;
 } __attribute__((aligned(sizeof(long))));
 	/*
 	 * On most architectures that alignment is already the case; but
@@ -846,6 +847,7 @@ struct file {
 	 * Must not be taken from IRQ context.
 	 */
 	spinlock_t		f_lock;
+	errseq_t		f_wb_err;
 	atomic_long_t		f_count;
 	unsigned int 		f_flags;
 	fmode_t			f_mode;
@@ -2520,6 +2522,62 @@ extern int filemap_fdatawrite_range(struct address_space *mapping,
 				loff_t start, loff_t end);
 extern int filemap_check_errors(struct address_space *mapping);
 
+extern void __filemap_set_wb_err(struct address_space *mapping, int err);
+extern int __must_check file_check_and_advance_wb_err(struct file *file);
+extern int __must_check file_write_and_wait_range(struct file *file,
+						loff_t start, loff_t end);
+
+/**
+ * filemap_set_wb_err - set a writeback error on an address_space
+ * @mapping: mapping in which to set writeback error
+ * @err: error to be set in mapping
+ *
+ * When writeback fails in some way, we must record that error so that
+ * userspace can be informed when fsync and the like are called.  We endeavor
+ * to report errors on any file that was open at the time of the error.  Some
+ * internal callers also need to know when writeback errors have occurred.
+ *
+ * When a writeback error occurs, most filesystems will want to call
+ * filemap_set_wb_err to record the error in the mapping so that it will be
+ * automatically reported whenever fsync is called on the file.
+ *
+ * FIXME: mention FS_* flag here?
+ */
+static inline void filemap_set_wb_err(struct address_space *mapping, int err)
+{
+	/* Fastpath for common case of no error */
+	if (unlikely(err))
+		__filemap_set_wb_err(mapping, err);
+}
+
+/**
+ * filemap_check_wb_error - has an error occurred since the mark was sampled?
+ * @mapping: mapping to check for writeback errors
+ * @since: previously-sampled errseq_t
+ *
+ * Grab the errseq_t value from the mapping, and see if it has changed "since"
+ * the given value was sampled.
+ *
+ * If it has then report the latest error set, otherwise return 0.
+ */
+static inline int filemap_check_wb_err(struct address_space *mapping,
+					errseq_t since)
+{
+	return errseq_check(&mapping->wb_err, since);
+}
+
+/**
+ * filemap_sample_wb_err - sample the current errseq_t to test for later errors
+ * @mapping: mapping to be sampled
+ *
+ * Writeback errors are always reported relative to a particular sample point
+ * in the past. This function provides those sample points.
+ */
+static inline errseq_t filemap_sample_wb_err(struct address_space *mapping)
+{
+	return errseq_sample(&mapping->wb_err);
+}
+
 extern int vfs_fsync_range(struct file *file, loff_t start, loff_t end,
 			   int datasync);
 extern int vfs_fsync(struct file *file, int datasync);
diff --git a/include/trace/events/filemap.h b/include/trace/events/filemap.h
index 42febb6bc1d5..ff91325b8123 100644
--- a/include/trace/events/filemap.h
+++ b/include/trace/events/filemap.h
@@ -10,6 +10,7 @@
 #include <linux/memcontrol.h>
 #include <linux/device.h>
 #include <linux/kdev_t.h>
+#include <linux/errseq.h>
 
 DECLARE_EVENT_CLASS(mm_filemap_op_page_cache,
 
@@ -52,6 +53,62 @@ DEFINE_EVENT(mm_filemap_op_page_cache, mm_filemap_add_to_page_cache,
 	TP_ARGS(page)
 	);
 
+TRACE_EVENT(filemap_set_wb_err,
+		TP_PROTO(struct address_space *mapping, errseq_t eseq),
+
+		TP_ARGS(mapping, eseq),
+
+		TP_STRUCT__entry(
+			__field(unsigned long, i_ino)
+			__field(dev_t, s_dev)
+			__field(errseq_t, errseq)
+		),
+
+		TP_fast_assign(
+			__entry->i_ino = mapping->host->i_ino;
+			__entry->errseq = eseq;
+			if (mapping->host->i_sb)
+				__entry->s_dev = mapping->host->i_sb->s_dev;
+			else
+				__entry->s_dev = mapping->host->i_rdev;
+		),
+
+		TP_printk("dev=%d:%d ino=0x%lx errseq=0x%x",
+			MAJOR(__entry->s_dev), MINOR(__entry->s_dev),
+			__entry->i_ino, __entry->errseq)
+);
+
+TRACE_EVENT(file_check_and_advance_wb_err,
+		TP_PROTO(struct file *file, errseq_t old),
+
+		TP_ARGS(file, old),
+
+		TP_STRUCT__entry(
+			__field(struct file *, file);
+			__field(unsigned long, i_ino)
+			__field(dev_t, s_dev)
+			__field(errseq_t, old)
+			__field(errseq_t, new)
+		),
+
+		TP_fast_assign(
+			__entry->file = file;
+			__entry->i_ino = file->f_mapping->host->i_ino;
+			if (file->f_mapping->host->i_sb)
+				__entry->s_dev =
+					file->f_mapping->host->i_sb->s_dev;
+			else
+				__entry->s_dev =
+					file->f_mapping->host->i_rdev;
+			__entry->old = old;
+			__entry->new = file->f_wb_err;
+		),
+
+		TP_printk("file=%p dev=%d:%d ino=0x%lx old=0x%x new=0x%x",
+			__entry->file, MAJOR(__entry->s_dev),
+			MINOR(__entry->s_dev), __entry->i_ino, __entry->old,
+			__entry->new)
+);
 #endif /* _TRACE_FILEMAP_H */
 
 /* This part must be outside protection */
diff --git a/mm/filemap.c b/mm/filemap.c
index eb99b5f23c61..5d03381dc0e0 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -553,6 +553,92 @@ int filemap_write_and_wait_range(struct address_space *mapping,
 }
 EXPORT_SYMBOL(filemap_write_and_wait_range);
 
+void __filemap_set_wb_err(struct address_space *mapping, int err)
+{
+	errseq_t eseq = __errseq_set(&mapping->wb_err, err);
+
+	trace_filemap_set_wb_err(mapping, eseq);
+}
+EXPORT_SYMBOL(__filemap_set_wb_err);
+
+/**
+ * file_check_and_advance_wb_err - report wb error (if any) that was previously
+ * 				   and advance wb_err to current one
+ * @file: struct file on which the error is being reported
+ *
+ * When userland calls fsync (or something like nfsd does the equivalent), we
+ * want to report any writeback errors that occurred since the last fsync (or
+ * since the file was opened if there haven't been any).
+ *
+ * Grab the wb_err from the mapping. If it matches what we have in the file,
+ * then just quickly return 0. The file is all caught up.
+ *
+ * If it doesn't match, then take the mapping value, set the "seen" flag in
+ * it and try to swap it into place. If it works, or another task beat us
+ * to it with the new value, then update the f_wb_err and return the error
+ * portion. The error at this point must be reported via proper channels
+ * (a'la fsync, or NFS COMMIT operation, etc.).
+ *
+ * While we handle mapping->wb_err with atomic operations, the f_wb_err
+ * value is protected by the f_lock since we must ensure that it reflects
+ * the latest value swapped in for this file descriptor.
+ */
+int file_check_and_advance_wb_err(struct file *file)
+{
+	int err = 0;
+	errseq_t old = READ_ONCE(file->f_wb_err);
+	struct address_space *mapping = file->f_mapping;
+
+	/* Locklessly handle the common case where nothing has changed */
+	if (errseq_check(&mapping->wb_err, old)) {
+		/* Something changed, must use slow path */
+		spin_lock(&file->f_lock);
+		old = file->f_wb_err;
+		err = errseq_check_and_advance(&mapping->wb_err,
+						&file->f_wb_err);
+		trace_file_check_and_advance_wb_err(file, old);
+		spin_unlock(&file->f_lock);
+	}
+	return err;
+}
+EXPORT_SYMBOL(file_check_and_advance_wb_err);
+
+/**
+ * file_write_and_wait_range - write out & wait on a file range
+ * @file:	file pointing to address_space with pages
+ * @lstart:	offset in bytes where the range starts
+ * @lend:	offset in bytes where the range ends (inclusive)
+ *
+ * Write out and wait upon file offsets lstart->lend, inclusive.
+ *
+ * Note that @lend is inclusive (describes the last byte to be written) so
+ * that this function can be used to write to the very end-of-file (end = -1).
+ *
+ * After writing out and waiting on the data, we check and advance the
+ * f_wb_err cursor to the latest value, and return any errors detected there.
+ */
+int file_write_and_wait_range(struct file *file, loff_t lstart, loff_t lend)
+{
+	int err = 0;
+	struct address_space *mapping = file->f_mapping;
+
+	if ((!dax_mapping(mapping) && mapping->nrpages) ||
+	    (dax_mapping(mapping) && mapping->nrexceptional)) {
+		int err2;
+
+		err = __filemap_fdatawrite_range(mapping, lstart, lend,
+						 WB_SYNC_ALL);
+		/* See comment of filemap_write_and_wait() */
+		if (err != -EIO)
+			__filemap_fdatawait_range(mapping, lstart, lend);
+		err2 = file_check_and_advance_wb_err(file);
+		if (!err)
+			err = err2;
+	}
+	return err;
+}
+EXPORT_SYMBOL(file_write_and_wait_range);
+
 /**
  * replace_page_cache_page - replace a pagecache page with a new one
  * @old:	page to be replaced
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 11/18] mm: set both AS_EIO/AS_ENOSPC and errseq_t in mapping_set_error
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (9 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 10/18] fs: new infrastructure for writeback error handling and reporting jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 13:19 ` [PATCH v8 12/18] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors jlayton
                   ` (6 subsequent siblings)
  17 siblings, 0 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

When a writeback error occurs, we want later callers to be able to pick
up that fact when they go to wait on that writeback to complete.
Traditionally, we've used AS_EIO/AS_ENOSPC flags to track that, but
that's problematic since only one "checker" will be informed when an
error occurs.

In later patches, we're going to want to convert many of these callers
to check for errors since a well-defined point in time. For now, ensure
that we can handle both sorts of checks by both setting errors in both
places when there is a writeback failure.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 include/linux/pagemap.h | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 316a19f6b635..28acc94e0f81 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -28,14 +28,33 @@ enum mapping_flags {
 	AS_NO_WRITEBACK_TAGS = 5,
 };
 
+/**
+ * mapping_set_error - record a writeback error in the address_space
+ * @mapping - the mapping in which an error should be set
+ * @error - the error to set in the mapping
+ *
+ * When writeback fails in some way, we must record that error so that
+ * userspace can be informed when fsync and the like are called.  We endeavor
+ * to report errors on any file that was open at the time of the error.  Some
+ * internal callers also need to know when writeback errors have occurred.
+ *
+ * When a writeback error occurs, most filesystems will want to call
+ * mapping_set_error to record the error in the mapping so that it can be
+ * reported when the application calls fsync(2).
+ */
 static inline void mapping_set_error(struct address_space *mapping, int error)
 {
-	if (unlikely(error)) {
-		if (error == -ENOSPC)
-			set_bit(AS_ENOSPC, &mapping->flags);
-		else
-			set_bit(AS_EIO, &mapping->flags);
-	}
+	if (likely(!error))
+		return;
+
+	/* Record in wb_err for checkers using errseq_t based tracking */
+	filemap_set_wb_err(mapping, error);
+
+	/* Record it in flags for now, for legacy callers */
+	if (error == -ENOSPC)
+		set_bit(AS_ENOSPC, &mapping->flags);
+	else
+		set_bit(AS_EIO, &mapping->flags);
 }
 
 static inline void mapping_set_unevictable(struct address_space *mapping)
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 12/18] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (10 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 11/18] mm: set both AS_EIO/AS_ENOSPC and errseq_t in mapping_set_error jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 17:11   ` Darrick J. Wong
  2017-06-29 13:19 ` [PATCH v8 13/18] dax: set errors in mapping when writeback fails jlayton
                   ` (5 subsequent siblings)
  17 siblings, 1 reply; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

Let's try to make this extra clear for fs authors.

Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 Documentation/filesystems/vfs.txt | 43 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 40 insertions(+), 3 deletions(-)

diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index f42b90687d40..1366043b3942 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -576,7 +576,42 @@ should clear PG_Dirty and set PG_Writeback.  It can be actually
 written at any point after PG_Dirty is clear.  Once it is known to be
 safe, PG_Writeback is cleared.
 
-Writeback makes use of a writeback_control structure...
+Writeback makes use of a writeback_control structure to direct the
+operations.  This gives the the writepage and writepages operations some
+information about the nature of and reason for the writeback request,
+and the constraints under which it is being done.  It is also used to
+return information back to the caller about the result of a writepage or
+writepages request.
+
+Handling errors during writeback
+--------------------------------
+Most applications that utilize the pagecache will periodically call
+fsync to ensure that data written has made it to the backing store.
+When there is an error during writeback, they expect that error to be
+reported when fsync is called.  After an error has been reported on one
+fsync, subsequent fsync calls on the same file descriptor should return
+0, unless further writeback errors have occurred since the previous
+fsync.
+
+Ideally, the kernel would report an error only on file descriptions on
+which writes were done that subsequently failed to be written back.  The
+generic pagecache infrastructure does not track the file descriptions
+that have dirtied each individual page however, so determining which
+file descriptors should get back an error is not possible.
+
+Instead, the generic writeback error tracking infrastructure in the
+kernel settles for reporting errors to fsync on all file descriptions
+that were open at the time that the error occurred.  In a situation with
+multiple writers, all of them will get back an error on a subsequent fsync,
+even if all of the writes done through that particular file descriptor
+succeeded (or even if there were no writes on that file descriptor at all).
+
+Filesystems that wish to use this infrastructure should call
+mapping_set_error to record the error in the address_space when it
+occurs.  Then, at the end of their fsync operation, they should call
+file_check_and_advance_wb_err to ensure that the struct file's error
+cursor has advanced to the correct point in the stream of errors emitted
+by the backing device(s).
 
 struct address_space_operations
 -------------------------------
@@ -804,7 +839,8 @@ struct address_space_operations {
 The File Object
 ===============
 
-A file object represents a file opened by a process.
+A file object represents a file opened by a process. This is also known
+as an "open file description" in POSIX parlance.
 
 
 struct file_operations
@@ -887,7 +923,8 @@ otherwise noted.
 
   release: called when the last reference to an open file is closed
 
-  fsync: called by the fsync(2) system call
+  fsync: called by the fsync(2) system call. Also see the section above
+	 entitled "Handling errors during writeback".
 
   fasync: called by the fcntl(2) system call when asynchronous
 	(non-blocking) mode is enabled for a file
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 13/18] dax: set errors in mapping when writeback fails
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (11 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 12/18] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 13:19 ` [PATCH v8 14/18] block: convert to errseq_t based writeback error tracking jlayton
                   ` (4 subsequent siblings)
  17 siblings, 0 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

Jan Kara's description for this patch is much better than mine, so I'm
quoting it verbatim here:

DAX currently doesn't set errors in the mapping when cache flushing
fails in dax_writeback_mapping_range(). Since this function can get
called only from fsync(2) or sync(2), this is actually as good as it can
currently get since we correctly propagate the error up from
dax_writeback_mapping_range() to filemap_fdatawrite()

However, in the future better writeback error handling will enable us to
properly report these errors on fsync(2) even if there are multiple file
descriptors open against the file or if sync(2) gets called before
fsync(2). So convert DAX to using standard error reporting through the
mapping.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-and-tested-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/dax.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/dax.c b/fs/dax.c
index c22eaf162f95..441280e15d5b 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -856,8 +856,10 @@ int dax_writeback_mapping_range(struct address_space *mapping,
 
 			ret = dax_writeback_one(bdev, dax_dev, mapping,
 					indices[i], pvec.pages[i]);
-			if (ret < 0)
+			if (ret < 0) {
+				mapping_set_error(mapping, ret);
 				goto out;
+			}
 		}
 	}
 out:
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 14/18] block: convert to errseq_t based writeback error tracking
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (12 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 13/18] dax: set errors in mapping when writeback fails jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 14:18   ` Christoph Hellwig
  2017-06-29 13:19 ` [PATCH v8 15/18] fs: convert __generic_file_fsync to use errseq_t based reporting jlayton
                   ` (3 subsequent siblings)
  17 siblings, 1 reply; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

This is a very minimal conversion to errseq_t based error tracking
for raw block device access. Just have it use the standard
file_write_and_wait_range call.

Note that there are internal callers that call sync_blockdev
and the like that are not affected by this. They'll continue
to use the AS_EIO/AS_ENOSPC flags for error reporting like
they always have for now.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/block_dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 4d62fe771587..bcb0be6e423a 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -624,7 +624,7 @@ int blkdev_fsync(struct file *filp, loff_t start, loff_t end, int datasync)
 	struct block_device *bdev = I_BDEV(bd_inode);
 	int error;
 	
-	error = filemap_write_and_wait_range(filp->f_mapping, start, end);
+	error = file_write_and_wait_range(filp, start, end);
 	if (error)
 		return error;
 
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 15/18] fs: convert __generic_file_fsync to use errseq_t based reporting
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (13 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 14/18] block: convert to errseq_t based writeback error tracking jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 13:19 ` [PATCH v8 16/18] ext4: use errseq_t based error handling for reporting data writeback errors jlayton
                   ` (2 subsequent siblings)
  17 siblings, 0 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/libfs.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index 1dec90819366..3aabe553fc45 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -974,7 +974,7 @@ int __generic_file_fsync(struct file *file, loff_t start, loff_t end,
 	int err;
 	int ret;
 
-	err = filemap_write_and_wait_range(inode->i_mapping, start, end);
+	err = file_write_and_wait_range(file, start, end);
 	if (err)
 		return err;
 
@@ -991,8 +991,11 @@ int __generic_file_fsync(struct file *file, loff_t start, loff_t end,
 
 out:
 	inode_unlock(inode);
-	err = filemap_check_errors(inode->i_mapping);
-	return ret ? ret : err;
+	/* check and advance again to catch errors after syncing out buffers */
+	err = file_check_and_advance_wb_err(file);
+	if (ret == 0)
+		ret = err;
+	return ret;
 }
 EXPORT_SYMBOL(__generic_file_fsync);
 
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 16/18] ext4: use errseq_t based error handling for reporting data writeback errors
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (14 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 15/18] fs: convert __generic_file_fsync to use errseq_t based reporting jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 14:12   ` Christoph Hellwig
  2017-06-29 13:19 ` [PATCH v8 17/18] xfs: minimal conversion to errseq_t writeback error reporting jlayton
  2017-06-29 13:19 ` [PATCH v8 18/18] btrfs: minimal conversion to errseq_t writeback error reporting on fsync jlayton
  17 siblings, 1 reply; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

Add a call to filemap_report_wb_err at the end of ext4_sync_file. This
will ensure that we check and advance the errseq_t in the file, which
allows us to track and report errors on all open fds when they occur.

Note that metadata writeback errors are not yet reported on all fds at
this point. That will be added in a later patch.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/ext4/fsync.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
index 9d549608fd30..d7cf0934c71c 100644
--- a/fs/ext4/fsync.c
+++ b/fs/ext4/fsync.c
@@ -100,8 +100,10 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	tid_t commit_tid;
 	bool needs_barrier = false;
 
-	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
-		return -EIO;
+	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb)))) {
+		ret = -EIO;
+		goto out;
+	}
 
 	J_ASSERT(ext4_journal_current_handle() == NULL);
 
@@ -124,9 +126,10 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 		goto out;
 	}
 
-	ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
+	ret = file_write_and_wait_range(file, start, end);
 	if (ret)
-		return ret;
+		goto out;
+
 	/*
 	 * data=writeback,ordered:
 	 *  The caller's filemap_fdatawrite()/wait will sync the data.
@@ -152,7 +155,7 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 		needs_barrier = true;
 	ret = jbd2_complete_transaction(journal, commit_tid);
 	if (needs_barrier) {
-	issue_flush:
+issue_flush:
 		err = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
 		if (!ret)
 			ret = err;
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 17/18] xfs: minimal conversion to errseq_t writeback error reporting
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (15 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 16/18] ext4: use errseq_t based error handling for reporting data writeback errors jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 14:12   ` Christoph Hellwig
  2017-06-29 17:13   ` Darrick J. Wong
  2017-06-29 13:19 ` [PATCH v8 18/18] btrfs: minimal conversion to errseq_t writeback error reporting on fsync jlayton
  17 siblings, 2 replies; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

Just check and advance the data errseq_t in struct file before
before returning from fsync on normal files. Internal filemap_*
callers are left as-is.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/xfs/xfs_file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 5fb5a0958a14..6600b264b0b6 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -140,7 +140,7 @@ xfs_file_fsync(
 
 	trace_xfs_file_fsync(ip);
 
-	error = filemap_write_and_wait_range(inode->i_mapping, start, end);
+	error = file_write_and_wait_range(file, start, end);
 	if (error)
 		return error;
 
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* [PATCH v8 18/18] btrfs: minimal conversion to errseq_t writeback error reporting on fsync
  2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
                   ` (16 preceding siblings ...)
  2017-06-29 13:19 ` [PATCH v8 17/18] xfs: minimal conversion to errseq_t writeback error reporting jlayton
@ 2017-06-29 13:19 ` jlayton
  2017-06-29 14:17   ` Christoph Hellwig
  17 siblings, 1 reply; 36+ messages in thread
From: jlayton @ 2017-06-29 13:19 UTC (permalink / raw)
  To: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

From: Jeff Layton <jlayton@redhat.com>

Just check and advance the errseq_t in the file before returning.
Internal callers of filemap_* functions are left as-is.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/btrfs/file.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index da1096eb1a40..1f57e1a523d9 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2011,7 +2011,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	struct btrfs_trans_handle *trans;
 	struct btrfs_log_ctx ctx;
-	int ret = 0;
+	int ret = 0, err;
 	bool full_sync = 0;
 	u64 len;
 
@@ -2030,7 +2030,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	 */
 	ret = start_ordered_ops(inode, start, end);
 	if (ret)
-		return ret;
+		goto out;
 
 	inode_lock(inode);
 	atomic_inc(&root->log_batch);
@@ -2227,6 +2227,9 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 		ret = btrfs_end_transaction(trans);
 	}
 out:
+	err = file_check_and_advance_wb_err(file);
+	if (!ret)
+		ret = err;
 	return ret > 0 ? -EIO : ret;
 }
 
-- 
2.13.0

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 10/18] fs: new infrastructure for writeback error handling and reporting
  2017-06-29 13:19 ` [PATCH v8 10/18] fs: new infrastructure for writeback error handling and reporting jlayton
@ 2017-06-29 13:45   ` Jeff Layton
  2017-06-29 17:52   ` Jeff Layton
  1 sibling, 0 replies; 36+ messages in thread
From: Jeff Layton @ 2017-06-29 13:45 UTC (permalink / raw)
  To: jlayton, Andrew Morton, Al Viro, Jan Kara, tytso, axboe,
	mawilcox, ross.zwisler, corbet, Chris Mason, Josef Bacik,
	David Sterba, Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

On Thu, 2017-06-29 at 09:19 -0400, jlayton@kernel.org wrote:
> From: Jeff Layton <jlayton@redhat.com>
> 
> Most filesystems currently use mapping_set_error and
> filemap_check_errors for setting and reporting/clearing writeback errors
> at the mapping level. filemap_check_errors is indirectly called from
> most of the filemap_fdatawait_* functions and from
> filemap_write_and_wait*. These functions are called from all sorts of
> contexts to wait on writeback to finish -- e.g. mostly in fsync, but
> also in truncate calls, getattr, etc.
> 
> The non-fsync callers are problematic. We should be reporting writeback
> errors during fsync, but many places spread over the tree clear out
> errors before they can be properly reported, or report errors at
> nonsensical times.
> 
> If I get -EIO on a stat() call, there is no reason for me to assume that
> it is because some previous writeback failed. The fact that it also
> clears out the error such that a subsequent fsync returns 0 is a bug,
> and a nasty one since that's potentially silent data corruption.
> 
> This patch adds a small bit of new infrastructure for setting and
> reporting errors during address_space writeback. While the above was my
> original impetus for adding this, I think it's also the case that
> current fsync semantics are just problematic for userland. Most
> applications that call fsync do so to ensure that the data they wrote
> has hit the backing store.
> 
> In the case where there are multiple writers to the file at the same
> time, this is really hard to determine. The first one to call fsync will
> see any stored error, and the rest get back 0. The processes with open
> fds may not be associated with one another in any way. They could even
> be in different containers, so ensuring coordination between all fsync
> callers is not really an option.
> 
> One way to remedy this would be to track what file descriptor was used
> to dirty the file, but that's rather cumbersome and would likely be
> slow. However, there is a simpler way to improve the semantics here
> without incurring too much overhead.
> 
> This set adds an errseq_t to struct address_space, and a corresponding
> one is added to struct file. Writeback errors are recorded in the
> mapping's errseq_t, and the one in struct file is used as the "since"
> value.
> 
> This changes the semantics of the Linux fsync implementation such that
> applications can now use it to determine whether there were any
> writeback errors since fsync(fd) was last called (or since the file was
> opened in the case of fsync having never been called).
> 
> Note that those writeback errors may have occurred when writing data
> that was dirtied via an entirely different fd, but that's the case now
> with the current mapping_set_error/filemap_check_error infrastructure.
> This will at least prevent you from getting a false report of success.
> 
> The new behavior is still consistent with the POSIX spec, and is more
> reliable for application developers. This patch just adds some basic
> infrastructure for doing this, and ensures that the f_wb_err "cursor"
> is properly set when a file is opened. Later patches will change the
> existing code to use this new infrastructure for reporting errors at
> fsync time.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> Reviewed-by: Jan Kara <jack@suse.cz>
> ---
>  drivers/dax/device.c           |  1 +
>  fs/block_dev.c                 |  1 +
>  fs/file_table.c                |  1 +
>  fs/open.c                      |  3 ++
>  include/linux/fs.h             | 60 ++++++++++++++++++++++++++++-
>  include/trace/events/filemap.h | 57 ++++++++++++++++++++++++++++
>  mm/filemap.c                   | 86 ++++++++++++++++++++++++++++++++++++++++++
>  7 files changed, 208 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index 006e657dfcb9..12943d19bfc4 100644
> --- a/drivers/dax/device.c
> +++ b/drivers/dax/device.c
> @@ -499,6 +499,7 @@ static int dax_open(struct inode *inode, struct file *filp)
>  	inode->i_mapping = __dax_inode->i_mapping;
>  	inode->i_mapping->host = __dax_inode;
>  	filp->f_mapping = inode->i_mapping;
> +	filp->f_wb_err = filemap_sample_wb_err(filp->f_mapping);
>  	filp->private_data = dev_dax;
>  	inode->i_flags = S_DAX;
>  
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 519599dddd36..4d62fe771587 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1743,6 +1743,7 @@ static int blkdev_open(struct inode * inode, struct file * filp)
>  		return -ENOMEM;
>  
>  	filp->f_mapping = bdev->bd_inode->i_mapping;
> +	filp->f_wb_err = filemap_sample_wb_err(filp->f_mapping);
>  
>  	return blkdev_get(bdev, filp->f_mode, filp);
>  }
> diff --git a/fs/file_table.c b/fs/file_table.c
> index 954d510b765a..72e861a35a7f 100644
> --- a/fs/file_table.c
> +++ b/fs/file_table.c
> @@ -168,6 +168,7 @@ struct file *alloc_file(const struct path *path, fmode_t mode,
>  	file->f_path = *path;
>  	file->f_inode = path->dentry->d_inode;
>  	file->f_mapping = path->dentry->d_inode->i_mapping;
> +	file->f_wb_err = filemap_sample_wb_err(file->f_mapping);
>  	if ((mode & FMODE_READ) &&
>  	     likely(fop->read || fop->read_iter))
>  		mode |= FMODE_CAN_READ;
> diff --git a/fs/open.c b/fs/open.c
> index cd0c5be8d012..280d4a963791 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -707,6 +707,9 @@ static int do_dentry_open(struct file *f,
>  	f->f_inode = inode;
>  	f->f_mapping = inode->i_mapping;
>  
> +	/* Ensure that we skip any errors that predate opening of the file */
> +	f->f_wb_err = filemap_sample_wb_err(f->f_mapping);
> +
>  	if (unlikely(f->f_flags & O_PATH)) {
>  		f->f_mode = FMODE_PATH;
>  		f->f_op = &empty_fops;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 74872c0f1c07..b524fd442057 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -30,7 +30,7 @@
>  #include <linux/percpu-rwsem.h>
>  #include <linux/workqueue.h>
>  #include <linux/delayed_call.h>
> -
> +#include <linux/errseq.h>
>  #include <asm/byteorder.h>
>  #include <uapi/linux/fs.h>
>  
> @@ -392,6 +392,7 @@ struct address_space {
>  	gfp_t			gfp_mask;	/* implicit gfp mask for allocations */
>  	struct list_head	private_list;	/* ditto */
>  	void			*private_data;	/* ditto */
> +	errseq_t		wb_err;
>  } __attribute__((aligned(sizeof(long))));
>  	/*
>  	 * On most architectures that alignment is already the case; but
> @@ -846,6 +847,7 @@ struct file {
>  	 * Must not be taken from IRQ context.
>  	 */
>  	spinlock_t		f_lock;
> +	errseq_t		f_wb_err;

Ahh, this field needs to be moved to the end of the struct to avoid
conflict with Jens' work. I'll fix that in my linux-next branch.

>  	atomic_long_t		f_count;
>  	unsigned int 		f_flags;
>  	fmode_t			f_mode;
> @@ -2520,6 +2522,62 @@ extern int filemap_fdatawrite_range(struct address_space *mapping,
>  				loff_t start, loff_t end);
>  extern int filemap_check_errors(struct address_space *mapping);
>  
> +extern void __filemap_set_wb_err(struct address_space *mapping, int err);
> +extern int __must_check file_check_and_advance_wb_err(struct file *file);
> +extern int __must_check file_write_and_wait_range(struct file *file,
> +						loff_t start, loff_t end);
> +
> +/**
> + * filemap_set_wb_err - set a writeback error on an address_space
> + * @mapping: mapping in which to set writeback error
> + * @err: error to be set in mapping
> + *
> + * When writeback fails in some way, we must record that error so that
> + * userspace can be informed when fsync and the like are called.  We endeavor
> + * to report errors on any file that was open at the time of the error.  Some
> + * internal callers also need to know when writeback errors have occurred.
> + *
> + * When a writeback error occurs, most filesystems will want to call
> + * filemap_set_wb_err to record the error in the mapping so that it will be
> + * automatically reported whenever fsync is called on the file.
> + *
> + * FIXME: mention FS_* flag here?
> + */
> +static inline void filemap_set_wb_err(struct address_space *mapping, int err)
> +{
> +	/* Fastpath for common case of no error */
> +	if (unlikely(err))
> +		__filemap_set_wb_err(mapping, err);
> +}
> +
> +/**
> + * filemap_check_wb_error - has an error occurred since the mark was sampled?
> + * @mapping: mapping to check for writeback errors
> + * @since: previously-sampled errseq_t
> + *
> + * Grab the errseq_t value from the mapping, and see if it has changed "since"
> + * the given value was sampled.
> + *
> + * If it has then report the latest error set, otherwise return 0.
> + */
> +static inline int filemap_check_wb_err(struct address_space *mapping,
> +					errseq_t since)
> +{
> +	return errseq_check(&mapping->wb_err, since);
> +}
> +
> +/**
> + * filemap_sample_wb_err - sample the current errseq_t to test for later errors
> + * @mapping: mapping to be sampled
> + *
> + * Writeback errors are always reported relative to a particular sample point
> + * in the past. This function provides those sample points.
> + */
> +static inline errseq_t filemap_sample_wb_err(struct address_space *mapping)
> +{
> +	return errseq_sample(&mapping->wb_err);
> +}
> +
>  extern int vfs_fsync_range(struct file *file, loff_t start, loff_t end,
>  			   int datasync);
>  extern int vfs_fsync(struct file *file, int datasync);
> diff --git a/include/trace/events/filemap.h b/include/trace/events/filemap.h
> index 42febb6bc1d5..ff91325b8123 100644
> --- a/include/trace/events/filemap.h
> +++ b/include/trace/events/filemap.h
> @@ -10,6 +10,7 @@
>  #include <linux/memcontrol.h>
>  #include <linux/device.h>
>  #include <linux/kdev_t.h>
> +#include <linux/errseq.h>
>  
>  DECLARE_EVENT_CLASS(mm_filemap_op_page_cache,
>  
> @@ -52,6 +53,62 @@ DEFINE_EVENT(mm_filemap_op_page_cache, mm_filemap_add_to_page_cache,
>  	TP_ARGS(page)
>  	);
>  
> +TRACE_EVENT(filemap_set_wb_err,
> +		TP_PROTO(struct address_space *mapping, errseq_t eseq),
> +
> +		TP_ARGS(mapping, eseq),
> +
> +		TP_STRUCT__entry(
> +			__field(unsigned long, i_ino)
> +			__field(dev_t, s_dev)
> +			__field(errseq_t, errseq)
> +		),
> +
> +		TP_fast_assign(
> +			__entry->i_ino = mapping->host->i_ino;
> +			__entry->errseq = eseq;
> +			if (mapping->host->i_sb)
> +				__entry->s_dev = mapping->host->i_sb->s_dev;
> +			else
> +				__entry->s_dev = mapping->host->i_rdev;
> +		),
> +
> +		TP_printk("dev=%d:%d ino=0x%lx errseq=0x%x",
> +			MAJOR(__entry->s_dev), MINOR(__entry->s_dev),
> +			__entry->i_ino, __entry->errseq)
> +);
> +
> +TRACE_EVENT(file_check_and_advance_wb_err,
> +		TP_PROTO(struct file *file, errseq_t old),
> +
> +		TP_ARGS(file, old),
> +
> +		TP_STRUCT__entry(
> +			__field(struct file *, file);
> +			__field(unsigned long, i_ino)
> +			__field(dev_t, s_dev)
> +			__field(errseq_t, old)
> +			__field(errseq_t, new)
> +		),
> +
> +		TP_fast_assign(
> +			__entry->file = file;
> +			__entry->i_ino = file->f_mapping->host->i_ino;
> +			if (file->f_mapping->host->i_sb)
> +				__entry->s_dev =
> +					file->f_mapping->host->i_sb->s_dev;
> +			else
> +				__entry->s_dev =
> +					file->f_mapping->host->i_rdev;
> +			__entry->old = old;
> +			__entry->new = file->f_wb_err;
> +		),
> +
> +		TP_printk("file=%p dev=%d:%d ino=0x%lx old=0x%x new=0x%x",
> +			__entry->file, MAJOR(__entry->s_dev),
> +			MINOR(__entry->s_dev), __entry->i_ino, __entry->old,
> +			__entry->new)
> +);
>  #endif /* _TRACE_FILEMAP_H */
>  
>  /* This part must be outside protection */
> diff --git a/mm/filemap.c b/mm/filemap.c
> index eb99b5f23c61..5d03381dc0e0 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -553,6 +553,92 @@ int filemap_write_and_wait_range(struct address_space *mapping,
>  }
>  EXPORT_SYMBOL(filemap_write_and_wait_range);
>  
> +void __filemap_set_wb_err(struct address_space *mapping, int err)
> +{
> +	errseq_t eseq = __errseq_set(&mapping->wb_err, err);
> +
> +	trace_filemap_set_wb_err(mapping, eseq);
> +}
> +EXPORT_SYMBOL(__filemap_set_wb_err);
> +
> +/**
> + * file_check_and_advance_wb_err - report wb error (if any) that was previously
> + * 				   and advance wb_err to current one
> + * @file: struct file on which the error is being reported
> + *
> + * When userland calls fsync (or something like nfsd does the equivalent), we
> + * want to report any writeback errors that occurred since the last fsync (or
> + * since the file was opened if there haven't been any).
> + *
> + * Grab the wb_err from the mapping. If it matches what we have in the file,
> + * then just quickly return 0. The file is all caught up.
> + *
> + * If it doesn't match, then take the mapping value, set the "seen" flag in
> + * it and try to swap it into place. If it works, or another task beat us
> + * to it with the new value, then update the f_wb_err and return the error
> + * portion. The error at this point must be reported via proper channels
> + * (a'la fsync, or NFS COMMIT operation, etc.).
> + *
> + * While we handle mapping->wb_err with atomic operations, the f_wb_err
> + * value is protected by the f_lock since we must ensure that it reflects
> + * the latest value swapped in for this file descriptor.
> + */
> +int file_check_and_advance_wb_err(struct file *file)
> +{
> +	int err = 0;
> +	errseq_t old = READ_ONCE(file->f_wb_err);
> +	struct address_space *mapping = file->f_mapping;
> +
> +	/* Locklessly handle the common case where nothing has changed */
> +	if (errseq_check(&mapping->wb_err, old)) {
> +		/* Something changed, must use slow path */
> +		spin_lock(&file->f_lock);
> +		old = file->f_wb_err;
> +		err = errseq_check_and_advance(&mapping->wb_err,
> +						&file->f_wb_err);
> +		trace_file_check_and_advance_wb_err(file, old);
> +		spin_unlock(&file->f_lock);
> +	}
> +	return err;
> +}
> +EXPORT_SYMBOL(file_check_and_advance_wb_err);
> +
> +/**
> + * file_write_and_wait_range - write out & wait on a file range
> + * @file:	file pointing to address_space with pages
> + * @lstart:	offset in bytes where the range starts
> + * @lend:	offset in bytes where the range ends (inclusive)
> + *
> + * Write out and wait upon file offsets lstart->lend, inclusive.
> + *
> + * Note that @lend is inclusive (describes the last byte to be written) so
> + * that this function can be used to write to the very end-of-file (end = -1).
> + *
> + * After writing out and waiting on the data, we check and advance the
> + * f_wb_err cursor to the latest value, and return any errors detected there.
> + */
> +int file_write_and_wait_range(struct file *file, loff_t lstart, loff_t lend)
> +{
> +	int err = 0;
> +	struct address_space *mapping = file->f_mapping;
> +
> +	if ((!dax_mapping(mapping) && mapping->nrpages) ||
> +	    (dax_mapping(mapping) && mapping->nrexceptional)) {
> +		int err2;
> +
> +		err = __filemap_fdatawrite_range(mapping, lstart, lend,
> +						 WB_SYNC_ALL);
> +		/* See comment of filemap_write_and_wait() */
> +		if (err != -EIO)
> +			__filemap_fdatawait_range(mapping, lstart, lend);
> +		err2 = file_check_and_advance_wb_err(file);
> +		if (!err)
> +			err = err2;
> +	}
> +	return err;
> +}
> +EXPORT_SYMBOL(file_write_and_wait_range);
> +
>  /**
>   * replace_page_cache_page - replace a pagecache page with a new one
>   * @old:	page to be replaced

-- 
Jeff Layton <jlayton@redhat.com>

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 16/18] ext4: use errseq_t based error handling for reporting data writeback errors
  2017-06-29 13:19 ` [PATCH v8 16/18] ext4: use errseq_t based error handling for reporting data writeback errors jlayton
@ 2017-06-29 14:12   ` Christoph Hellwig
  2017-06-29 20:26     ` Jeff Layton
  0 siblings, 1 reply; 36+ messages in thread
From: Christoph Hellwig @ 2017-06-29 14:12 UTC (permalink / raw)
  To: jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong, Carlos Maiolino, Eryu Guan, David Howells,
	Christoph Hellwig, Liu Bo, linux-fsdevel, linux-mm, linux-ext4,
	linux-xfs, linux-btrfs, linux-block

> -	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
> -		return -EIO;
> +	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb)))) {
> +		ret = -EIO;
> +		goto out;
> +	}

This just seems to add a call to trace_ext4_sync_file_exit for this
case, which seems unrelated to the patch.

>  	if (ret)
> -		return ret;
> +		goto out;
> +

Same here.

>  	/*
>  	 * data=writeback,ordered:
>  	 *  The caller's filemap_fdatawrite()/wait will sync the data.
> @@ -152,7 +155,7 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
>  		needs_barrier = true;
>  	ret = jbd2_complete_transaction(journal, commit_tid);
>  	if (needs_barrier) {
> -	issue_flush:
> +issue_flush:
>  		err = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);

And while I much prefer your new label placement it also doesn't
seem to belong into this patch.

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 17/18] xfs: minimal conversion to errseq_t writeback error reporting
  2017-06-29 13:19 ` [PATCH v8 17/18] xfs: minimal conversion to errseq_t writeback error reporting jlayton
@ 2017-06-29 14:12   ` Christoph Hellwig
  2017-06-30 16:45     ` Jeff Layton
  2017-06-29 17:13   ` Darrick J. Wong
  1 sibling, 1 reply; 36+ messages in thread
From: Christoph Hellwig @ 2017-06-29 14:12 UTC (permalink / raw)
  To: jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong, Carlos Maiolino, Eryu Guan, David Howells,
	Christoph Hellwig, Liu Bo, linux-fsdevel, linux-mm, linux-ext4,
	linux-xfs, linux-btrfs, linux-block

Nice and simple, this looks great!

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

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 18/18] btrfs: minimal conversion to errseq_t writeback error reporting on fsync
  2017-06-29 13:19 ` [PATCH v8 18/18] btrfs: minimal conversion to errseq_t writeback error reporting on fsync jlayton
@ 2017-06-29 14:17   ` Christoph Hellwig
  2017-06-29 20:32     ` Jeff Layton
  0 siblings, 1 reply; 36+ messages in thread
From: Christoph Hellwig @ 2017-06-29 14:17 UTC (permalink / raw)
  To: jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong, Carlos Maiolino, Eryu Guan, David Howells,
	Christoph Hellwig, Liu Bo, linux-fsdevel, linux-mm, linux-ext4,
	linux-xfs, linux-btrfs, linux-block

On Thu, Jun 29, 2017 at 09:19:54AM -0400, jlayton@kernel.org wrote:
> From: Jeff Layton <jlayton@redhat.com>
> 
> Just check and advance the errseq_t in the file before returning.
> Internal callers of filemap_* functions are left as-is.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  fs/btrfs/file.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index da1096eb1a40..1f57e1a523d9 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -2011,7 +2011,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
>  	struct btrfs_root *root = BTRFS_I(inode)->root;
>  	struct btrfs_trans_handle *trans;
>  	struct btrfs_log_ctx ctx;
> -	int ret = 0;
> +	int ret = 0, err;
>  	bool full_sync = 0;
>  	u64 len;
>  
> @@ -2030,7 +2030,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
>  	 */
>  	ret = start_ordered_ops(inode, start, end);
>  	if (ret)
> -		return ret;
> +		goto out;
>  
>  	inode_lock(inode);
>  	atomic_inc(&root->log_batch);
> @@ -2227,6 +2227,9 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
>  		ret = btrfs_end_transaction(trans);
>  	}
>  out:
> +	err = file_check_and_advance_wb_err(file);
> +	if (!ret)
> +		ret = err;
>  	return ret > 0 ? -EIO : ret;

This means that we'll lose the exact error returned from
start_ordered_ops.  Beyond that I can't really provide good feedback
as the btrfs fsync code looks so much different from all the other
fs fsync code..

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 14/18] block: convert to errseq_t based writeback error tracking
  2017-06-29 13:19 ` [PATCH v8 14/18] block: convert to errseq_t based writeback error tracking jlayton
@ 2017-06-29 14:18   ` Christoph Hellwig
  0 siblings, 0 replies; 36+ messages in thread
From: Christoph Hellwig @ 2017-06-29 14:18 UTC (permalink / raw)
  To: jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong, Carlos Maiolino, Eryu Guan, David Howells,
	Christoph Hellwig, Liu Bo, linux-fsdevel, linux-mm, linux-ext4,
	linux-xfs, linux-btrfs, linux-block

Looks good,

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

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 03/18] fs: check for writeback errors after syncing out buffers in generic_file_fsync
  2017-06-29 13:19 ` [PATCH v8 03/18] fs: check for writeback errors after syncing out buffers in generic_file_fsync jlayton
@ 2017-06-29 14:19   ` Christoph Hellwig
  2017-06-29 20:17     ` Jeff Layton
  0 siblings, 1 reply; 36+ messages in thread
From: Christoph Hellwig @ 2017-06-29 14:19 UTC (permalink / raw)
  To: jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong, Carlos Maiolino, Eryu Guan, David Howells,
	Christoph Hellwig, Liu Bo, linux-fsdevel, linux-mm, linux-ext4,
	linux-xfs, linux-btrfs, linux-block

On Thu, Jun 29, 2017 at 09:19:39AM -0400, jlayton@kernel.org wrote:
> From: Jeff Layton <jlayton@redhat.com>
> 
> ext2 currently does a test+clear of the AS_EIO flag, which is
> is problematic for some coming changes.
> 
> What we really need to do instead is call filemap_check_errors
> in __generic_file_fsync after syncing out the buffers. That
> will be sufficient for this case, and help other callers detect
> these errors properly as well.
> 
> With that, we don't need to twiddle it in ext2.

Seems like much of this code is getting replaced later in the
series..

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 12/18] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors
  2017-06-29 13:19 ` [PATCH v8 12/18] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors jlayton
@ 2017-06-29 17:11   ` Darrick J. Wong
  2017-06-29 18:13     ` Jeff Layton
  0 siblings, 1 reply; 36+ messages in thread
From: Darrick J. Wong @ 2017-06-29 17:11 UTC (permalink / raw)
  To: jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

On Thu, Jun 29, 2017 at 09:19:48AM -0400, jlayton@kernel.org wrote:
> From: Jeff Layton <jlayton@redhat.com>
> 
> Let's try to make this extra clear for fs authors.
> 
> Cc: Jan Kara <jack@suse.cz>
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  Documentation/filesystems/vfs.txt | 43 ++++++++++++++++++++++++++++++++++++---
>  1 file changed, 40 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
> index f42b90687d40..1366043b3942 100644
> --- a/Documentation/filesystems/vfs.txt
> +++ b/Documentation/filesystems/vfs.txt
> @@ -576,7 +576,42 @@ should clear PG_Dirty and set PG_Writeback.  It can be actually
>  written at any point after PG_Dirty is clear.  Once it is known to be
>  safe, PG_Writeback is cleared.
>  
> -Writeback makes use of a writeback_control structure...
> +Writeback makes use of a writeback_control structure to direct the
> +operations.  This gives the the writepage and writepages operations some
> +information about the nature of and reason for the writeback request,
> +and the constraints under which it is being done.  It is also used to
> +return information back to the caller about the result of a writepage or
> +writepages request.
> +
> +Handling errors during writeback
> +--------------------------------
> +Most applications that utilize the pagecache will periodically call
> +fsync to ensure that data written has made it to the backing store.

/me wonders if this sentence ought to be worded more strongly, e.g.

"Applications that utilize the pagecache must call a data
synchronization syscall such as fsync, fdatasync, or msync to ensure
that data written has made it to the backing store."

I'm also wondering -- fdatasync and msync will also report any writeback
errors that have happened anywhere (like fsync), since they all map to
vfs_fsync_range, correct?  If so, I think it worth it to state
explicitly that the other *sync methods behave the same as fsync w.r.t.
writeback error reporting.

--D

> +When there is an error during writeback, they expect that error to be
> +reported when fsync is called.  After an error has been reported on one
> +fsync, subsequent fsync calls on the same file descriptor should return
> +0, unless further writeback errors have occurred since the previous
> +fsync.
> +
> +Ideally, the kernel would report an error only on file descriptions on
> +which writes were done that subsequently failed to be written back.  The
> +generic pagecache infrastructure does not track the file descriptions
> +that have dirtied each individual page however, so determining which
> +file descriptors should get back an error is not possible.
> +
> +Instead, the generic writeback error tracking infrastructure in the
> +kernel settles for reporting errors to fsync on all file descriptions
> +that were open at the time that the error occurred.  In a situation with
> +multiple writers, all of them will get back an error on a subsequent fsync,
> +even if all of the writes done through that particular file descriptor
> +succeeded (or even if there were no writes on that file descriptor at all).
> +
> +Filesystems that wish to use this infrastructure should call
> +mapping_set_error to record the error in the address_space when it
> +occurs.  Then, at the end of their fsync operation, they should call
> +file_check_and_advance_wb_err to ensure that the struct file's error
> +cursor has advanced to the correct point in the stream of errors emitted
> +by the backing device(s).
>  
>  struct address_space_operations
>  -------------------------------
> @@ -804,7 +839,8 @@ struct address_space_operations {
>  The File Object
>  ===============
>  
> -A file object represents a file opened by a process.
> +A file object represents a file opened by a process. This is also known
> +as an "open file description" in POSIX parlance.
>  
>  
>  struct file_operations
> @@ -887,7 +923,8 @@ otherwise noted.
>  
>    release: called when the last reference to an open file is closed
>  
> -  fsync: called by the fsync(2) system call
> +  fsync: called by the fsync(2) system call. Also see the section above
> +	 entitled "Handling errors during writeback".
>  
>    fasync: called by the fcntl(2) system call when asynchronous
>  	(non-blocking) mode is enabled for a file
> -- 
> 2.13.0
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 17/18] xfs: minimal conversion to errseq_t writeback error reporting
  2017-06-29 13:19 ` [PATCH v8 17/18] xfs: minimal conversion to errseq_t writeback error reporting jlayton
  2017-06-29 14:12   ` Christoph Hellwig
@ 2017-06-29 17:13   ` Darrick J. Wong
  1 sibling, 0 replies; 36+ messages in thread
From: Darrick J. Wong @ 2017-06-29 17:13 UTC (permalink / raw)
  To: jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

On Thu, Jun 29, 2017 at 09:19:53AM -0400, jlayton@kernel.org wrote:
> From: Jeff Layton <jlayton@redhat.com>
> 
> Just check and advance the data errseq_t in struct file before
> before returning from fsync on normal files. Internal filemap_*
> callers are left as-is.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/xfs/xfs_file.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 5fb5a0958a14..6600b264b0b6 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -140,7 +140,7 @@ xfs_file_fsync(
>  
>  	trace_xfs_file_fsync(ip);
>  
> -	error = filemap_write_and_wait_range(inode->i_mapping, start, end);
> +	error = file_write_and_wait_range(file, start, end);
>  	if (error)
>  		return error;
>  
> -- 
> 2.13.0
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 10/18] fs: new infrastructure for writeback error handling and reporting
  2017-06-29 13:19 ` [PATCH v8 10/18] fs: new infrastructure for writeback error handling and reporting jlayton
  2017-06-29 13:45   ` Jeff Layton
@ 2017-06-29 17:52   ` Jeff Layton
  1 sibling, 0 replies; 36+ messages in thread
From: Jeff Layton @ 2017-06-29 17:52 UTC (permalink / raw)
  To: jlayton, Andrew Morton, Al Viro, Jan Kara, tytso, axboe,
	mawilcox, ross.zwisler, corbet, Chris Mason, Josef Bacik,
	David Sterba, Darrick J . Wong
  Cc: Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

On Thu, 2017-06-29 at 09:19 -0400, jlayton@kernel.org wrote:
> From: Jeff Layton <jlayton@redhat.com>
> 
> Most filesystems currently use mapping_set_error and
> filemap_check_errors for setting and reporting/clearing writeback errors
> at the mapping level. filemap_check_errors is indirectly called from
> most of the filemap_fdatawait_* functions and from
> filemap_write_and_wait*. These functions are called from all sorts of
> contexts to wait on writeback to finish -- e.g. mostly in fsync, but
> also in truncate calls, getattr, etc.
> 
> The non-fsync callers are problematic. We should be reporting writeback
> errors during fsync, but many places spread over the tree clear out
> errors before they can be properly reported, or report errors at
> nonsensical times.
> 
> If I get -EIO on a stat() call, there is no reason for me to assume that
> it is because some previous writeback failed. The fact that it also
> clears out the error such that a subsequent fsync returns 0 is a bug,
> and a nasty one since that's potentially silent data corruption.
> 
> This patch adds a small bit of new infrastructure for setting and
> reporting errors during address_space writeback. While the above was my
> original impetus for adding this, I think it's also the case that
> current fsync semantics are just problematic for userland. Most
> applications that call fsync do so to ensure that the data they wrote
> has hit the backing store.
> 
> In the case where there are multiple writers to the file at the same
> time, this is really hard to determine. The first one to call fsync will
> see any stored error, and the rest get back 0. The processes with open
> fds may not be associated with one another in any way. They could even
> be in different containers, so ensuring coordination between all fsync
> callers is not really an option.
> 
> One way to remedy this would be to track what file descriptor was used
> to dirty the file, but that's rather cumbersome and would likely be
> slow. However, there is a simpler way to improve the semantics here
> without incurring too much overhead.
> 
> This set adds an errseq_t to struct address_space, and a corresponding
> one is added to struct file. Writeback errors are recorded in the
> mapping's errseq_t, and the one in struct file is used as the "since"
> value.
> 
> This changes the semantics of the Linux fsync implementation such that
> applications can now use it to determine whether there were any
> writeback errors since fsync(fd) was last called (or since the file was
> opened in the case of fsync having never been called).
> 
> Note that those writeback errors may have occurred when writing data
> that was dirtied via an entirely different fd, but that's the case now
> with the current mapping_set_error/filemap_check_error infrastructure.
> This will at least prevent you from getting a false report of success.
> 
> The new behavior is still consistent with the POSIX spec, and is more
> reliable for application developers. This patch just adds some basic
> infrastructure for doing this, and ensures that the f_wb_err "cursor"
> is properly set when a file is opened. Later patches will change the
> existing code to use this new infrastructure for reporting errors at
> fsync time.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> Reviewed-by: Jan Kara <jack@suse.cz>
> ---
>  drivers/dax/device.c           |  1 +
>  fs/block_dev.c                 |  1 +
>  fs/file_table.c                |  1 +
>  fs/open.c                      |  3 ++
>  include/linux/fs.h             | 60 ++++++++++++++++++++++++++++-
>  include/trace/events/filemap.h | 57 ++++++++++++++++++++++++++++
>  mm/filemap.c                   | 86 ++++++++++++++++++++++++++++++++++++++++++
>  7 files changed, 208 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index 006e657dfcb9..12943d19bfc4 100644
> --- a/drivers/dax/device.c
> +++ b/drivers/dax/device.c
> @@ -499,6 +499,7 @@ static int dax_open(struct inode *inode, struct file *filp)
>  	inode->i_mapping = __dax_inode->i_mapping;
>  	inode->i_mapping->host = __dax_inode;
>  	filp->f_mapping = inode->i_mapping;
> +	filp->f_wb_err = filemap_sample_wb_err(filp->f_mapping);
>  	filp->private_data = dev_dax;
>  	inode->i_flags = S_DAX;
>  
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 519599dddd36..4d62fe771587 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1743,6 +1743,7 @@ static int blkdev_open(struct inode * inode, struct file * filp)
>  		return -ENOMEM;
>  
>  	filp->f_mapping = bdev->bd_inode->i_mapping;
> +	filp->f_wb_err = filemap_sample_wb_err(filp->f_mapping);
>  
>  	return blkdev_get(bdev, filp->f_mode, filp);
>  }
> diff --git a/fs/file_table.c b/fs/file_table.c
> index 954d510b765a..72e861a35a7f 100644
> --- a/fs/file_table.c
> +++ b/fs/file_table.c
> @@ -168,6 +168,7 @@ struct file *alloc_file(const struct path *path, fmode_t mode,
>  	file->f_path = *path;
>  	file->f_inode = path->dentry->d_inode;
>  	file->f_mapping = path->dentry->d_inode->i_mapping;
> +	file->f_wb_err = filemap_sample_wb_err(file->f_mapping);
>  	if ((mode & FMODE_READ) &&
>  	     likely(fop->read || fop->read_iter))
>  		mode |= FMODE_CAN_READ;
> diff --git a/fs/open.c b/fs/open.c
> index cd0c5be8d012..280d4a963791 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -707,6 +707,9 @@ static int do_dentry_open(struct file *f,
>  	f->f_inode = inode;
>  	f->f_mapping = inode->i_mapping;
>  
> +	/* Ensure that we skip any errors that predate opening of the file */
> +	f->f_wb_err = filemap_sample_wb_err(f->f_mapping);
> +
>  	if (unlikely(f->f_flags & O_PATH)) {
>  		f->f_mode = FMODE_PATH;
>  		f->f_op = &empty_fops;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 74872c0f1c07..b524fd442057 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -30,7 +30,7 @@
>  #include <linux/percpu-rwsem.h>
>  #include <linux/workqueue.h>
>  #include <linux/delayed_call.h>
> -
> +#include <linux/errseq.h>
>  #include <asm/byteorder.h>
>  #include <uapi/linux/fs.h>
>  
> @@ -392,6 +392,7 @@ struct address_space {
>  	gfp_t			gfp_mask;	/* implicit gfp mask for allocations */
>  	struct list_head	private_list;	/* ditto */
>  	void			*private_data;	/* ditto */
> +	errseq_t		wb_err;
>  } __attribute__((aligned(sizeof(long))));
>  	/*
>  	 * On most architectures that alignment is already the case; but
> @@ -846,6 +847,7 @@ struct file {
>  	 * Must not be taken from IRQ context.
>  	 */
>  	spinlock_t		f_lock;
> +	errseq_t		f_wb_err;
>  	atomic_long_t		f_count;
>  	unsigned int 		f_flags;
>  	fmode_t			f_mode;
> @@ -2520,6 +2522,62 @@ extern int filemap_fdatawrite_range(struct address_space *mapping,
>  				loff_t start, loff_t end);
>  extern int filemap_check_errors(struct address_space *mapping);
>  
> +extern void __filemap_set_wb_err(struct address_space *mapping, int err);
> +extern int __must_check file_check_and_advance_wb_err(struct file *file);
> +extern int __must_check file_write_and_wait_range(struct file *file,
> +						loff_t start, loff_t end);
> +
> +/**
> + * filemap_set_wb_err - set a writeback error on an address_space
> + * @mapping: mapping in which to set writeback error
> + * @err: error to be set in mapping
> + *
> + * When writeback fails in some way, we must record that error so that
> + * userspace can be informed when fsync and the like are called.  We endeavor
> + * to report errors on any file that was open at the time of the error.  Some
> + * internal callers also need to know when writeback errors have occurred.
> + *
> + * When a writeback error occurs, most filesystems will want to call
> + * filemap_set_wb_err to record the error in the mapping so that it will be
> + * automatically reported whenever fsync is called on the file.
> + *
> + * FIXME: mention FS_* flag here?
> + */
> +static inline void filemap_set_wb_err(struct address_space *mapping, int err)
> +{
> +	/* Fastpath for common case of no error */
> +	if (unlikely(err))
> +		__filemap_set_wb_err(mapping, err);
> +}
> +
> +/**
> + * filemap_check_wb_error - has an error occurred since the mark was sampled?
> + * @mapping: mapping to check for writeback errors
> + * @since: previously-sampled errseq_t
> + *
> + * Grab the errseq_t value from the mapping, and see if it has changed "since"
> + * the given value was sampled.
> + *
> + * If it has then report the latest error set, otherwise return 0.
> + */
> +static inline int filemap_check_wb_err(struct address_space *mapping,
> +					errseq_t since)
> +{
> +	return errseq_check(&mapping->wb_err, since);
> +}
> +
> +/**
> + * filemap_sample_wb_err - sample the current errseq_t to test for later errors
> + * @mapping: mapping to be sampled
> + *
> + * Writeback errors are always reported relative to a particular sample point
> + * in the past. This function provides those sample points.
> + */
> +static inline errseq_t filemap_sample_wb_err(struct address_space *mapping)
> +{
> +	return errseq_sample(&mapping->wb_err);
> +}
> +
>  extern int vfs_fsync_range(struct file *file, loff_t start, loff_t end,
>  			   int datasync);
>  extern int vfs_fsync(struct file *file, int datasync);
> diff --git a/include/trace/events/filemap.h b/include/trace/events/filemap.h
> index 42febb6bc1d5..ff91325b8123 100644
> --- a/include/trace/events/filemap.h
> +++ b/include/trace/events/filemap.h
> @@ -10,6 +10,7 @@
>  #include <linux/memcontrol.h>
>  #include <linux/device.h>
>  #include <linux/kdev_t.h>
> +#include <linux/errseq.h>
>  
>  DECLARE_EVENT_CLASS(mm_filemap_op_page_cache,
>  
> @@ -52,6 +53,62 @@ DEFINE_EVENT(mm_filemap_op_page_cache, mm_filemap_add_to_page_cache,
>  	TP_ARGS(page)
>  	);
>  
> +TRACE_EVENT(filemap_set_wb_err,
> +		TP_PROTO(struct address_space *mapping, errseq_t eseq),
> +
> +		TP_ARGS(mapping, eseq),
> +
> +		TP_STRUCT__entry(
> +			__field(unsigned long, i_ino)
> +			__field(dev_t, s_dev)
> +			__field(errseq_t, errseq)
> +		),
> +
> +		TP_fast_assign(
> +			__entry->i_ino = mapping->host->i_ino;
> +			__entry->errseq = eseq;
> +			if (mapping->host->i_sb)
> +				__entry->s_dev = mapping->host->i_sb->s_dev;
> +			else
> +				__entry->s_dev = mapping->host->i_rdev;
> +		),
> +
> +		TP_printk("dev=%d:%d ino=0x%lx errseq=0x%x",
> +			MAJOR(__entry->s_dev), MINOR(__entry->s_dev),
> +			__entry->i_ino, __entry->errseq)
> +);
> +
> +TRACE_EVENT(file_check_and_advance_wb_err,
> +		TP_PROTO(struct file *file, errseq_t old),
> +
> +		TP_ARGS(file, old),
> +
> +		TP_STRUCT__entry(
> +			__field(struct file *, file);
> +			__field(unsigned long, i_ino)
> +			__field(dev_t, s_dev)
> +			__field(errseq_t, old)
> +			__field(errseq_t, new)
> +		),
> +
> +		TP_fast_assign(
> +			__entry->file = file;
> +			__entry->i_ino = file->f_mapping->host->i_ino;
> +			if (file->f_mapping->host->i_sb)
> +				__entry->s_dev =
> +					file->f_mapping->host->i_sb->s_dev;
> +			else
> +				__entry->s_dev =
> +					file->f_mapping->host->i_rdev;
> +			__entry->old = old;
> +			__entry->new = file->f_wb_err;
> +		),
> +
> +		TP_printk("file=%p dev=%d:%d ino=0x%lx old=0x%x new=0x%x",
> +			__entry->file, MAJOR(__entry->s_dev),
> +			MINOR(__entry->s_dev), __entry->i_ino, __entry->old,
> +			__entry->new)
> +);
>  #endif /* _TRACE_FILEMAP_H */
>  
>  /* This part must be outside protection */
> diff --git a/mm/filemap.c b/mm/filemap.c
> index eb99b5f23c61..5d03381dc0e0 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -553,6 +553,92 @@ int filemap_write_and_wait_range(struct address_space *mapping,
>  }
>  EXPORT_SYMBOL(filemap_write_and_wait_range);
>  
> +void __filemap_set_wb_err(struct address_space *mapping, int err)
> +{
> +	errseq_t eseq = __errseq_set(&mapping->wb_err, err);
> +
> +	trace_filemap_set_wb_err(mapping, eseq);
> +}
> +EXPORT_SYMBOL(__filemap_set_wb_err);
> +
> +/**
> + * file_check_and_advance_wb_err - report wb error (if any) that was previously
> + * 				   and advance wb_err to current one
> + * @file: struct file on which the error is being reported
> + *
> + * When userland calls fsync (or something like nfsd does the equivalent), we
> + * want to report any writeback errors that occurred since the last fsync (or
> + * since the file was opened if there haven't been any).
> + *
> + * Grab the wb_err from the mapping. If it matches what we have in the file,
> + * then just quickly return 0. The file is all caught up.
> + *
> + * If it doesn't match, then take the mapping value, set the "seen" flag in
> + * it and try to swap it into place. If it works, or another task beat us
> + * to it with the new value, then update the f_wb_err and return the error
> + * portion. The error at this point must be reported via proper channels
> + * (a'la fsync, or NFS COMMIT operation, etc.).
> + *
> + * While we handle mapping->wb_err with atomic operations, the f_wb_err
> + * value is protected by the f_lock since we must ensure that it reflects
> + * the latest value swapped in for this file descriptor.
> + */
> +int file_check_and_advance_wb_err(struct file *file)
> +{
> +	int err = 0;
> +	errseq_t old = READ_ONCE(file->f_wb_err);
> +	struct address_space *mapping = file->f_mapping;
> +
> +	/* Locklessly handle the common case where nothing has changed */
> +	if (errseq_check(&mapping->wb_err, old)) {
> +		/* Something changed, must use slow path */
> +		spin_lock(&file->f_lock);
> +		old = file->f_wb_err;
> +		err = errseq_check_and_advance(&mapping->wb_err,
> +						&file->f_wb_err);
> +		trace_file_check_and_advance_wb_err(file, old);
> +		spin_unlock(&file->f_lock);
> +	}
> +	return err;
> +}
> +EXPORT_SYMBOL(file_check_and_advance_wb_err);
> +
> +/**
> + * file_write_and_wait_range - write out & wait on a file range
> + * @file:	file pointing to address_space with pages
> + * @lstart:	offset in bytes where the range starts
> + * @lend:	offset in bytes where the range ends (inclusive)
> + *
> + * Write out and wait upon file offsets lstart->lend, inclusive.
> + *
> + * Note that @lend is inclusive (describes the last byte to be written) so
> + * that this function can be used to write to the very end-of-file (end = -1).
> + *
> + * After writing out and waiting on the data, we check and advance the
> + * f_wb_err cursor to the latest value, and return any errors detected there.
> + */
> +int file_write_and_wait_range(struct file *file, loff_t lstart, loff_t lend)
> +{
> +	int err = 0;
> +	struct address_space *mapping = file->f_mapping;
> +
> +	if ((!dax_mapping(mapping) && mapping->nrpages) ||
> +	    (dax_mapping(mapping) && mapping->nrexceptional)) {
> +		int err2;
> +
> +		err = __filemap_fdatawrite_range(mapping, lstart, lend,
> +						 WB_SYNC_ALL);
> +		/* See comment of filemap_write_and_wait() */
> +		if (err != -EIO)
> +			__filemap_fdatawait_range(mapping, lstart, lend);
> +		err2 = file_check_and_advance_wb_err(file);
> +		if (!err)
> +			err = err2;

Braino on my part here.

We need to do the check and advance unconditionally in this function to
handle the case where the nrpages and/or nrexceptional are 0. Fixed in
my tree.

> +	}
> +	return err;
> +}
> +EXPORT_SYMBOL(file_write_and_wait_range);
> +
>  /**
>   * replace_page_cache_page - replace a pagecache page with a new one
>   * @old:	page to be replaced

-- 
Jeff Layton <jlayton@redhat.com>

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 12/18] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors
  2017-06-29 17:11   ` Darrick J. Wong
@ 2017-06-29 18:13     ` Jeff Layton
  2017-06-29 18:21       ` Matthew Wilcox
  0 siblings, 1 reply; 36+ messages in thread
From: Jeff Layton @ 2017-06-29 18:13 UTC (permalink / raw)
  To: Darrick J. Wong, jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Carlos Maiolino, Eryu Guan, David Howells, Christoph Hellwig,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

On Thu, 2017-06-29 at 10:11 -0700, Darrick J. Wong wrote:
> On Thu, Jun 29, 2017 at 09:19:48AM -0400, jlayton@kernel.org wrote:
> > From: Jeff Layton <jlayton@redhat.com>
> > 
> > Let's try to make this extra clear for fs authors.
> > 
> > Cc: Jan Kara <jack@suse.cz>
> > Signed-off-by: Jeff Layton <jlayton@redhat.com>
> > ---
> >  Documentation/filesystems/vfs.txt | 43 ++++++++++++++++++++++++++++++++++++---
> >  1 file changed, 40 insertions(+), 3 deletions(-)
> > 
> > diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
> > index f42b90687d40..1366043b3942 100644
> > --- a/Documentation/filesystems/vfs.txt
> > +++ b/Documentation/filesystems/vfs.txt
> > @@ -576,7 +576,42 @@ should clear PG_Dirty and set PG_Writeback.  It can be actually
> >  written at any point after PG_Dirty is clear.  Once it is known to be
> >  safe, PG_Writeback is cleared.
> >  
> > -Writeback makes use of a writeback_control structure...
> > +Writeback makes use of a writeback_control structure to direct the
> > +operations.  This gives the the writepage and writepages operations some
> > +information about the nature of and reason for the writeback request,
> > +and the constraints under which it is being done.  It is also used to
> > +return information back to the caller about the result of a writepage or
> > +writepages request.
> > +
> > +Handling errors during writeback
> > +--------------------------------
> > +Most applications that utilize the pagecache will periodically call
> > +fsync to ensure that data written has made it to the backing store.
> 
> /me wonders if this sentence ought to be worded more strongly, e.g.
> 
> "Applications that utilize the pagecache must call a data
> synchronization syscall such as fsync, fdatasync, or msync to ensure
> that data written has made it to the backing store."
> 

Well...only if they care about the data. There are some that don't. :)

> I'm also wondering -- fdatasync and msync will also report any writeback
> errors that have happened anywhere (like fsync), since they all map to
> vfs_fsync_range, correct?  If so, I think it worth it to state
> explicitly that the other *sync methods behave the same as fsync w.r.t.
> writeback error reporting.
> 

Good point. I'll fix this to make it clear that fsync, msync and
fdatasync all advance the error cursor in the same way.

While we're on the subject...

What should we do about sync_file_range here? It doesn't currently call
any filesystem operations directly, so we don't have a good way to make
it selectively use errseq_t handling there.

I could resurrect the FS_* flag for that, though I don't really like
that. Should I just go ahead and convert it over to use errseq_t under
the theory that most callers will eventually want that anyway?

Thanks for the review so far!

> > +When there is an error during writeback, they expect that error to be
> > +reported when fsync is called.  After an error has been reported on one
> > +fsync, subsequent fsync calls on the same file descriptor should return
> > +0, unless further writeback errors have occurred since the previous
> > +fsync.
> > +
> > +Ideally, the kernel would report an error only on file descriptions on
> > +which writes were done that subsequently failed to be written back.  The
> > +generic pagecache infrastructure does not track the file descriptions
> > +that have dirtied each individual page however, so determining which
> > +file descriptors should get back an error is not possible.
> > +
> > +Instead, the generic writeback error tracking infrastructure in the
> > +kernel settles for reporting errors to fsync on all file descriptions
> > +that were open at the time that the error occurred.  In a situation with
> > +multiple writers, all of them will get back an error on a subsequent fsync,
> > +even if all of the writes done through that particular file descriptor
> > +succeeded (or even if there were no writes on that file descriptor at all).
> > +
> > +Filesystems that wish to use this infrastructure should call
> > +mapping_set_error to record the error in the address_space when it
> > +occurs.  Then, at the end of their fsync operation, they should call
> > +file_check_and_advance_wb_err to ensure that the struct file's error
> > +cursor has advanced to the correct point in the stream of errors emitted
> > +by the backing device(s).
> >  
> >  struct address_space_operations
> >  -------------------------------
> > @@ -804,7 +839,8 @@ struct address_space_operations {
> >  The File Object
> >  ===============
> >  
> > -A file object represents a file opened by a process.
> > +A file object represents a file opened by a process. This is also known
> > +as an "open file description" in POSIX parlance.
> >  
> >  
> >  struct file_operations
> > @@ -887,7 +923,8 @@ otherwise noted.
> >  
> >    release: called when the last reference to an open file is closed
> >  
> > -  fsync: called by the fsync(2) system call
> > +  fsync: called by the fsync(2) system call. Also see the section above
> > +	 entitled "Handling errors during writeback".
> >  
> >    fasync: called by the fcntl(2) system call when asynchronous
> >  	(non-blocking) mode is enabled for a file
> > -- 
> > 2.13.0
> > 
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Jeff Layton <jlayton@poochiereds.net>

^ permalink raw reply	[flat|nested] 36+ messages in thread

* RE: [PATCH v8 12/18] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors
  2017-06-29 18:13     ` Jeff Layton
@ 2017-06-29 18:21       ` Matthew Wilcox
  2017-06-29 20:42         ` Jeff Layton
  0 siblings, 1 reply; 36+ messages in thread
From: Matthew Wilcox @ 2017-06-29 18:21 UTC (permalink / raw)
  To: Jeff Layton, Darrick J. Wong, jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, ross.zwisler,
	corbet, Chris Mason, Josef Bacik, David Sterba, Carlos Maiolino,
	Eryu Guan, David Howells, Christoph Hellwig, Liu Bo,
	linux-fsdevel, linux-mm, linux-ext4, linux-xfs, linux-btrfs,
	linux-block

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^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 03/18] fs: check for writeback errors after syncing out buffers in generic_file_fsync
  2017-06-29 14:19   ` Christoph Hellwig
@ 2017-06-29 20:17     ` Jeff Layton
  0 siblings, 0 replies; 36+ messages in thread
From: Jeff Layton @ 2017-06-29 20:17 UTC (permalink / raw)
  To: Christoph Hellwig, jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong, Carlos Maiolino, Eryu Guan, David Howells,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

On Thu, 2017-06-29 at 07:19 -0700, Christoph Hellwig wrote:
> On Thu, Jun 29, 2017 at 09:19:39AM -0400, jlayton@kernel.org wrote:
> > From: Jeff Layton <jlayton@redhat.com>
> > 
> > ext2 currently does a test+clear of the AS_EIO flag, which is
> > is problematic for some coming changes.
> > 
> > What we really need to do instead is call filemap_check_errors
> > in __generic_file_fsync after syncing out the buffers. That
> > will be sufficient for this case, and help other callers detect
> > these errors properly as well.
> > 
> > With that, we don't need to twiddle it in ext2.
> 
> Seems like much of this code is getting replaced later in the
> series..


It does. I suppose I could squash this in with the __generic_file_fsync
patch.

-- 
Jeff Layton <jlayton@poochiereds.net>

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 16/18] ext4: use errseq_t based error handling for reporting data writeback errors
  2017-06-29 14:12   ` Christoph Hellwig
@ 2017-06-29 20:26     ` Jeff Layton
  0 siblings, 0 replies; 36+ messages in thread
From: Jeff Layton @ 2017-06-29 20:26 UTC (permalink / raw)
  To: Christoph Hellwig, jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong, Carlos Maiolino, Eryu Guan, David Howells,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

On Thu, 2017-06-29 at 07:12 -0700, Christoph Hellwig wrote:
> > -	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
> > -		return -EIO;
> > +	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb)))) {
> > +		ret = -EIO;
> > +		goto out;
> > +	}
> 
> This just seems to add a call to trace_ext4_sync_file_exit for this
> case, which seems unrelated to the patch.
> 
> >  	if (ret)
> > -		return ret;
> > +		goto out;
> > +
> 
> Same here.
> 
> >  	/*
> >  	 * data=writeback,ordered:
> >  	 *  The caller's filemap_fdatawrite()/wait will sync the data.
> > @@ -152,7 +155,7 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> >  		needs_barrier = true;
> >  	ret = jbd2_complete_transaction(journal, commit_tid);
> >  	if (needs_barrier) {
> > -	issue_flush:
> > +issue_flush:
> >  		err = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
> 
> And while I much prefer your new label placement it also doesn't
> seem to belong into this patch.

I revised the patch description earlier to say:

    While we're at it, ensure we always "goto out" instead of just
    returning directly, so that we always hit the exit tracepoint.

...but I'm fine with taking that out if you prefer.
-- 
Jeff Layton <jlayton@poochiereds.net>

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 18/18] btrfs: minimal conversion to errseq_t writeback error reporting on fsync
  2017-06-29 14:17   ` Christoph Hellwig
@ 2017-06-29 20:32     ` Jeff Layton
  0 siblings, 0 replies; 36+ messages in thread
From: Jeff Layton @ 2017-06-29 20:32 UTC (permalink / raw)
  To: Christoph Hellwig, jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong, Carlos Maiolino, Eryu Guan, David Howells,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

On Thu, 2017-06-29 at 07:17 -0700, Christoph Hellwig wrote:
> On Thu, Jun 29, 2017 at 09:19:54AM -0400, jlayton@kernel.org wrote:
> > From: Jeff Layton <jlayton@redhat.com>
> > 
> > Just check and advance the errseq_t in the file before returning.
> > Internal callers of filemap_* functions are left as-is.
> > 
> > Signed-off-by: Jeff Layton <jlayton@redhat.com>
> > ---
> >  fs/btrfs/file.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > index da1096eb1a40..1f57e1a523d9 100644
> > --- a/fs/btrfs/file.c
> > +++ b/fs/btrfs/file.c
> > @@ -2011,7 +2011,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> >  	struct btrfs_root *root = BTRFS_I(inode)->root;
> >  	struct btrfs_trans_handle *trans;
> >  	struct btrfs_log_ctx ctx;
> > -	int ret = 0;
> > +	int ret = 0, err;
> >  	bool full_sync = 0;
> >  	u64 len;
> >  
> > @@ -2030,7 +2030,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> >  	 */
> >  	ret = start_ordered_ops(inode, start, end);
> >  	if (ret)
> > -		return ret;
> > +		goto out;
> >  
> >  	inode_lock(inode);
> >  	atomic_inc(&root->log_batch);
> > @@ -2227,6 +2227,9 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> >  		ret = btrfs_end_transaction(trans);
> >  	}
> >  out:
> > +	err = file_check_and_advance_wb_err(file);
> > +	if (!ret)
> > +		ret = err;
> >  	return ret > 0 ? -EIO : ret;
> 
> This means that we'll lose the exact error returned from
> start_ordered_ops.  Beyond that I can't really provide good feedback
> as the btrfs fsync code looks so much different from all the other
> fs fsync code..

Well, no...we'll keep the error from start_ordered_ops if there was one.
 We just advance the cursor past any stored error in that case without
returning it.

I have another fix for this patch too: there's a call to
filemap_check_errors in this function that I think should probably use
filemap_check_wb_err instead. Fixed in my tree.

I do agree though that while this works in my testing I'd like the btrfs
guys to ACK this as I don't fully grok the btrfs fsync code at all.
-- 
Jeff Layton <jlayton@poochiereds.net>

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 12/18] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors
  2017-06-29 18:21       ` Matthew Wilcox
@ 2017-06-29 20:42         ` Jeff Layton
  0 siblings, 0 replies; 36+ messages in thread
From: Jeff Layton @ 2017-06-29 20:42 UTC (permalink / raw)
  To: Matthew Wilcox, Darrick J. Wong, jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, ross.zwisler,
	corbet, Chris Mason, Josef Bacik, David Sterba, Carlos Maiolino,
	Eryu Guan, David Howells, Christoph Hellwig, Liu Bo,
	linux-fsdevel, linux-mm, linux-ext4, linux-xfs, linux-btrfs,
	linux-block

On Thu, 2017-06-29 at 18:21 +0000, Matthew Wilcox wrote:
> From: Jeff Layton [mailto:jlayton@poochiereds.net]
> > On Thu, 2017-06-29 at 10:11 -0700, Darrick J. Wong wrote:
> > > On Thu, Jun 29, 2017 at 09:19:48AM -0400, jlayton@kernel.org wrote:
> > > > +Handling errors during writeback
> > > > +--------------------------------
> > > > +Most applications that utilize the pagecache will periodically call
> > > > +fsync to ensure that data written has made it to the backing store.
> > > 
> > > /me wonders if this sentence ought to be worded more strongly, e.g.
> > > 
> > > "Applications that utilize the pagecache must call a data
> > > synchronization syscall such as fsync, fdatasync, or msync to ensure
> > > that data written has made it to the backing store."
> > 
> > Well...only if they care about the data. There are some that don't. :)
> 
> Also, applications don't "utilize the pagecache"; filesystems use the pagecache.
> Applications may or may not use cached I/O.  How about this:
> 

I meant "applications that do buffered I/O" as opposed to O_DIRECT, but
yeah that's not very clear.


> Applications which care about data integrity and use cached I/O will
> periodically call fsync(), msync() or fdatasync() to ensure that their
> data is durable.
> 
> > What should we do about sync_file_range here? It doesn't currently call
> > any filesystem operations directly, so we don't have a good way to make
> > it selectively use errseq_t handling there.
> > 
> > I could resurrect the FS_* flag for that, though I don't really like
> > that. Should I just go ahead and convert it over to use errseq_t under
> > the theory that most callers will eventually want that anyway?
> 
> I think so.

Ok, I'll leave that for the next pile of patches though.

Here's a revised section

------------------------------8<--------------------------------
Handling errors during writeback
--------------------------------
Most applications that do buffered I/O will periodically call a file
synchronization call (fsync, fdatasync, msync or sync_file_range) to
ensure that data written has made it to the backing store.  When there
is an error during writeback, they expect that error to be reported when
a file sync request is made.  After an error has been reported on one
request, subsequent requests on the same file descriptor should return
0, unless further writeback errors have occurred since the previous file
syncronization.

Ideally, the kernel would report errors only on file descriptions on
which writes were done that subsequently failed to be written back.  The
generic pagecache infrastructure does not track the file descriptions
that have dirtied each individual page however, so determining which
file descriptors should get back an error is not possible.

Instead, the generic writeback error tracking infrastructure in the
kernel settles for reporting errors to fsync on all file descriptions
that were open at the time that the error occurred.  In a situation with
multiple writers, all of them will get back an error on a subsequent
fsync,
even if all of the writes done through that particular file descriptor
succeeded (or even if there were no writes on that file descriptor at
all).

Filesystems that wish to use this infrastructure should call
mapping_set_error to record the error in the address_space when it
occurs.  Then, after writing back data from the pagecache in their
file->fsync operation, they should call file_check_and_advance_wb_err to
ensure that the struct file's error cursor has advanced to the correct
point in the stream of errors emitted by the backing device(s).
------------------------------8<--------------------------------

Thanks for the review so far!
-- 
Jeff Layton <jlayton@poochiereds.net>

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 17/18] xfs: minimal conversion to errseq_t writeback error reporting
  2017-06-29 14:12   ` Christoph Hellwig
@ 2017-06-30 16:45     ` Jeff Layton
  2017-06-30 16:49       ` Christoph Hellwig
  0 siblings, 1 reply; 36+ messages in thread
From: Jeff Layton @ 2017-06-30 16:45 UTC (permalink / raw)
  To: Christoph Hellwig, jlayton
  Cc: Andrew Morton, Al Viro, Jan Kara, tytso, axboe, mawilcox,
	ross.zwisler, corbet, Chris Mason, Josef Bacik, David Sterba,
	Darrick J . Wong, Carlos Maiolino, Eryu Guan, David Howells,
	Liu Bo, linux-fsdevel, linux-mm, linux-ext4, linux-xfs,
	linux-btrfs, linux-block

On Thu, 2017-06-29 at 07:12 -0700, Christoph Hellwig wrote:
> Nice and simple, this looks great!
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Thanks! I think this turned out to be a lot cleaner too.

For filesystems that use filemap_write_and_wait_range today this now
becomes a pretty straight conversion to file_write_and_wait_range -- one
liner patches for the most part.

I've started rolling patches to do that, but now I'm wondering...

Should I aim to do that with an individual patch for each fs, or is it
better to do a swath of them all at once in a single patch here?
-- 
Jeff Layton <jlayton@redhat.com>

^ permalink raw reply	[flat|nested] 36+ messages in thread

* Re: [PATCH v8 17/18] xfs: minimal conversion to errseq_t writeback error reporting
  2017-06-30 16:45     ` Jeff Layton
@ 2017-06-30 16:49       ` Christoph Hellwig
  0 siblings, 0 replies; 36+ messages in thread
From: Christoph Hellwig @ 2017-06-30 16:49 UTC (permalink / raw)
  To: Jeff Layton
  Cc: Christoph Hellwig, jlayton, Andrew Morton, Al Viro, Jan Kara,
	tytso, axboe, mawilcox, ross.zwisler, corbet, Chris Mason,
	Josef Bacik, David Sterba, Darrick J . Wong, Carlos Maiolino,
	Eryu Guan, David Howells, Liu Bo, linux-fsdevel, linux-mm,
	linux-ext4, linux-xfs, linux-btrfs, linux-block

On Fri, Jun 30, 2017 at 12:45:54PM -0400, Jeff Layton wrote:
> Should I aim to do that with an individual patch for each fs, or is it
> better to do a swath of them all at once in a single patch here?

I'd be perfectly happy with one big patch for all the trivial
conversions.

^ permalink raw reply	[flat|nested] 36+ messages in thread

end of thread, back to index

Thread overview: 36+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-06-29 13:19 [PATCH v8 00/18] fs: enhanced writeback error reporting with errseq_t (pile #1) jlayton
2017-06-29 13:19 ` [PATCH v8 01/18] fs: remove call_fsync helper function jlayton
2017-06-29 13:19 ` [PATCH v8 02/18] buffer: use mapping_set_error instead of setting the flag jlayton
2017-06-29 13:19 ` [PATCH v8 03/18] fs: check for writeback errors after syncing out buffers in generic_file_fsync jlayton
2017-06-29 14:19   ` Christoph Hellwig
2017-06-29 20:17     ` Jeff Layton
2017-06-29 13:19 ` [PATCH v8 04/18] buffer: set errors in mapping at the time that the error occurs jlayton
2017-06-29 13:19 ` [PATCH v8 05/18] jbd2: don't clear and reset errors after waiting on writeback jlayton
2017-06-29 13:19 ` [PATCH v8 06/18] mm: clear AS_EIO/AS_ENOSPC when writeback initiation fails jlayton
2017-06-29 13:19 ` [PATCH v8 07/18] mm: don't TestClearPageError in __filemap_fdatawait_range jlayton
2017-06-29 13:19 ` [PATCH v8 08/18] mm: clean up error handling in write_one_page jlayton
2017-06-29 13:19 ` [PATCH v8 09/18] lib: add errseq_t type and infrastructure for handling it jlayton
2017-06-29 13:19 ` [PATCH v8 10/18] fs: new infrastructure for writeback error handling and reporting jlayton
2017-06-29 13:45   ` Jeff Layton
2017-06-29 17:52   ` Jeff Layton
2017-06-29 13:19 ` [PATCH v8 11/18] mm: set both AS_EIO/AS_ENOSPC and errseq_t in mapping_set_error jlayton
2017-06-29 13:19 ` [PATCH v8 12/18] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors jlayton
2017-06-29 17:11   ` Darrick J. Wong
2017-06-29 18:13     ` Jeff Layton
2017-06-29 18:21       ` Matthew Wilcox
2017-06-29 20:42         ` Jeff Layton
2017-06-29 13:19 ` [PATCH v8 13/18] dax: set errors in mapping when writeback fails jlayton
2017-06-29 13:19 ` [PATCH v8 14/18] block: convert to errseq_t based writeback error tracking jlayton
2017-06-29 14:18   ` Christoph Hellwig
2017-06-29 13:19 ` [PATCH v8 15/18] fs: convert __generic_file_fsync to use errseq_t based reporting jlayton
2017-06-29 13:19 ` [PATCH v8 16/18] ext4: use errseq_t based error handling for reporting data writeback errors jlayton
2017-06-29 14:12   ` Christoph Hellwig
2017-06-29 20:26     ` Jeff Layton
2017-06-29 13:19 ` [PATCH v8 17/18] xfs: minimal conversion to errseq_t writeback error reporting jlayton
2017-06-29 14:12   ` Christoph Hellwig
2017-06-30 16:45     ` Jeff Layton
2017-06-30 16:49       ` Christoph Hellwig
2017-06-29 17:13   ` Darrick J. Wong
2017-06-29 13:19 ` [PATCH v8 18/18] btrfs: minimal conversion to errseq_t writeback error reporting on fsync jlayton
2017-06-29 14:17   ` Christoph Hellwig
2017-06-29 20:32     ` Jeff Layton

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