[PATCH v6 00/20] fs: enhanced writeback error reporting with errseq_t (pile #1)

[PATCH v6 00/20] fs: enhanced writeback error reporting with errseq_t (pile #1)

[Jeff Layton]

v6:
===
This is the sixth posting of the patchset to revamp the way writeback
errors are tracked and reported.

This is a smaller set than the last one. The main difference from the
last set is that this one just adds errseq_t based error reporting for
the purposes of fsync, while leaving the internal callers of filemap_*
functions and the like largely untouched.

Some of these patches have been posted separately, but I'm re-posting
them here to make it clear that they're prerequisites to the later
patches in the series.

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 though, 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 the error flags 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 set 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 error checking is done using the traditional flag
based checks. The only real difference here is more reliable reporting
of errors at fsync.

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

Testing:
========
I've primarily been testing this with a couple of new xfstests that I
will post separately. These tests use dm-error fault injection to flip
the underlying block device to start throwing I/O errors, and then test
the behavior of the filesystem layer on top of that.

Jeff Layton (20):
  mm: fix mapping_set_error call in me_pagecache_dirty
  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
  mm: don't TestClearPageError in __filemap_fdatawait_range
  mm: drop "wait" parameter from write_one_page
  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: tracepoints for writeback error events
  mm: set both AS_EIO/AS_ENOSPC and errseq_t in mapping_set_error
  fs: add a new fstype flag to indicate how writeback errors are tracked
  Documentation: flesh out the section in vfs.txt on storing and
    reporting writeback errors
  dax: set errors in mapping when writeback fails
  fs: have call_fsync call filemap_report_wb_err if FS_WB_ERRSEQ is set
  block: convert to errseq_t based writeback error tracking
  fs: add f_md_wb_err field to struct file for tracking metadata errors
  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 |  48 ++++++++-
 drivers/dax/device.c              |   1 +
 fs/block_dev.c                    |   2 +
 fs/btrfs/super.c                  |   2 +-
 fs/buffer.c                       |  20 ++--
 fs/dax.c                          |  18 +++-
 fs/exofs/dir.c                    |   2 +-
 fs/ext2/dir.c                     |   2 +-
 fs/ext2/file.c                    |   2 +-
 fs/ext4/dir.c                     |   8 +-
 fs/ext4/file.c                    |   5 +-
 fs/ext4/fsync.c                   |  23 ++++-
 fs/ext4/super.c                   |   6 +-
 fs/file_table.c                   |   1 +
 fs/gfs2/lops.c                    |   2 +-
 fs/jfs/jfs_metapage.c             |   4 +-
 fs/libfs.c                        |   3 +-
 fs/minix/dir.c                    |   2 +-
 fs/open.c                         |   3 +
 fs/sysv/dir.c                     |   2 +-
 fs/ufs/dir.c                      |   2 +-
 fs/xfs/xfs_super.c                |   2 +-
 include/linux/buffer_head.h       |   1 +
 include/linux/errseq.h            |  19 ++++
 include/linux/fs.h                |  80 +++++++++++++--
 include/linux/mm.h                |   2 +-
 include/linux/pagemap.h           |  31 ++++--
 include/trace/events/filemap.h    |  52 ++++++++++
 lib/Makefile                      |   2 +-
 lib/errseq.c                      | 208 ++++++++++++++++++++++++++++++++++++++
 mm/filemap.c                      |  91 ++++++++++++++---
 mm/memory-failure.c               |   2 +-
 mm/page-writeback.c               |  21 ++--
 33 files changed, 595 insertions(+), 74 deletions(-)
 create mode 100644 include/linux/errseq.h
 create mode 100644 lib/errseq.c

-- 
2.13.0

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[PATCH v6 01/20] mm: fix mapping_set_error call in me_pagecache_dirty

[Jeff Layton]

The error code should be negative. Since this ends up in the default
case anyway, this is harmless, but it's less confusing to negate it.
Also, later patches will require a negative error code here.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 mm/memory-failure.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 342fac9ba89b..55bc61791fe1 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -684,7 +684,7 @@ static int me_pagecache_dirty(struct page *p, unsigned long pfn)
 		 * the first EIO, but we're not worse than other parts
 		 * of the kernel.
 		 */
-		mapping_set_error(mapping, EIO);
+		mapping_set_error(mapping, -EIO);
 	}
 
 	return me_pagecache_clean(p, pfn);
-- 
2.13.0

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[PATCH v6 02/20] buffer: use mapping_set_error instead of setting the flag

[Jeff Layton]

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

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[PATCH v6 03/20] fs: check for writeback errors after syncing out buffers in generic_file_fsync

[Jeff Layton]

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 | 2 +-
 fs/libfs.c     | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/ext2/file.c b/fs/ext2/file.c
index b21891a6bfca..ed00e7ae0ef3 100644
--- a/fs/ext2/file.c
+++ b/fs/ext2/file.c
@@ -177,7 +177,7 @@ int ext2_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 	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");
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

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[PATCH v6 04/20] buffer: set errors in mapping at the time that the error occurs

[Jeff Layton]

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>
---
 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

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[PATCH v6 05/20] mm: don't TestClearPageError in __filemap_fdatawait_range

[Jeff Layton]

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 6f1be573a5e6..1de71753de28 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -376,17 +376,16 @@ 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) &&
@@ -403,14 +402,11 @@ 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;
 }
 
 /**
@@ -430,14 +426,8 @@ 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

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[PATCH v6 06/20] mm: drop "wait" parameter from write_one_page

[Jeff Layton]

The callers all set it to 1.

Also, make it clear that this function will not set any sort of AS_*
error, and that the caller must do so if necessary. No existing caller
uses this on normal files, so none of them need it.

Also, add __must_check here since, in general, the callers need to
handle an error here in some fashion.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/exofs/dir.c        |  2 +-
 fs/ext2/dir.c         |  2 +-
 fs/jfs/jfs_metapage.c |  4 ++--
 fs/minix/dir.c        |  2 +-
 fs/sysv/dir.c         |  2 +-
 fs/ufs/dir.c          |  2 +-
 include/linux/mm.h    |  2 +-
 mm/page-writeback.c   | 14 +++++++-------
 8 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/fs/exofs/dir.c b/fs/exofs/dir.c
index 8eeb694332fe..98233a97b7b8 100644
--- a/fs/exofs/dir.c
+++ b/fs/exofs/dir.c
@@ -72,7 +72,7 @@ static int exofs_commit_chunk(struct page *page, loff_t pos, unsigned len)
 	set_page_dirty(page);
 
 	if (IS_DIRSYNC(dir))
-		err = write_one_page(page, 1);
+		err = write_one_page(page);
 	else
 		unlock_page(page);
 
diff --git a/fs/ext2/dir.c b/fs/ext2/dir.c
index d9650c9508e4..e2709695b177 100644
--- a/fs/ext2/dir.c
+++ b/fs/ext2/dir.c
@@ -100,7 +100,7 @@ static int ext2_commit_chunk(struct page *page, loff_t pos, unsigned len)
 	}
 
 	if (IS_DIRSYNC(dir)) {
-		err = write_one_page(page, 1);
+		err = write_one_page(page);
 		if (!err)
 			err = sync_inode_metadata(dir, 1);
 	} else {
diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
index 489aaa1403e5..744fa3c079e6 100644
--- a/fs/jfs/jfs_metapage.c
+++ b/fs/jfs/jfs_metapage.c
@@ -711,7 +711,7 @@ void force_metapage(struct metapage *mp)
 	get_page(page);
 	lock_page(page);
 	set_page_dirty(page);
-	write_one_page(page, 1);
+	write_one_page(page);
 	clear_bit(META_forcewrite, &mp->flag);
 	put_page(page);
 }
@@ -756,7 +756,7 @@ void release_metapage(struct metapage * mp)
 		set_page_dirty(page);
 		if (test_bit(META_sync, &mp->flag)) {
 			clear_bit(META_sync, &mp->flag);
-			write_one_page(page, 1);
+			write_one_page(page);
 			lock_page(page); /* write_one_page unlocks the page */
 		}
 	} else if (mp->lsn)	/* discard_metapage doesn't remove it */
diff --git a/fs/minix/dir.c b/fs/minix/dir.c
index 7edc9b395700..baa9721f1299 100644
--- a/fs/minix/dir.c
+++ b/fs/minix/dir.c
@@ -57,7 +57,7 @@ static int dir_commit_chunk(struct page *page, loff_t pos, unsigned len)
 		mark_inode_dirty(dir);
 	}
 	if (IS_DIRSYNC(dir))
-		err = write_one_page(page, 1);
+		err = write_one_page(page);
 	else
 		unlock_page(page);
 	return err;
diff --git a/fs/sysv/dir.c b/fs/sysv/dir.c
index 5bdae85ceef7..f5191cb2c947 100644
--- a/fs/sysv/dir.c
+++ b/fs/sysv/dir.c
@@ -45,7 +45,7 @@ static int dir_commit_chunk(struct page *page, loff_t pos, unsigned len)
 		mark_inode_dirty(dir);
 	}
 	if (IS_DIRSYNC(dir))
-		err = write_one_page(page, 1);
+		err = write_one_page(page);
 	else
 		unlock_page(page);
 	return err;
diff --git a/fs/ufs/dir.c b/fs/ufs/dir.c
index de01b8f2aa78..48609f1d9580 100644
--- a/fs/ufs/dir.c
+++ b/fs/ufs/dir.c
@@ -53,7 +53,7 @@ static int ufs_commit_chunk(struct page *page, loff_t pos, unsigned len)
 		mark_inode_dirty(dir);
 	}
 	if (IS_DIRSYNC(dir))
-		err = write_one_page(page, 1);
+		err = write_one_page(page);
 	else
 		unlock_page(page);
 	return err;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b892e95d4929..c0b1759304ec 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2199,7 +2199,7 @@ extern void filemap_map_pages(struct vm_fault *vmf,
 extern int filemap_page_mkwrite(struct vm_fault *vmf);
 
 /* mm/page-writeback.c */
-int write_one_page(struct page *page, int wait);
+int __must_check write_one_page(struct page *page);
 void task_dirty_inc(struct task_struct *tsk);
 
 /* readahead.c */
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 143c1c25d680..b901fe52b153 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2366,15 +2366,16 @@ int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
 }
 
 /**
- * write_one_page - write out a single page and optionally wait on I/O
+ * write_one_page - write out a single page and wait on I/O
  * @page: the page to write
- * @wait: if true, wait on writeout
  *
  * 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.
+ * 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.
  */
-int write_one_page(struct page *page, int wait)
+int write_one_page(struct page *page)
 {
 	struct address_space *mapping = page->mapping;
 	int ret = 0;
@@ -2385,13 +2386,12 @@ int write_one_page(struct page *page, int wait)
 
 	BUG_ON(!PageLocked(page));
 
-	if (wait)
-		wait_on_page_writeback(page);
+	wait_on_page_writeback(page);
 
 	if (clear_page_dirty_for_io(page)) {
 		get_page(page);
 		ret = mapping->a_ops->writepage(page, &wbc);
-		if (ret == 0 && wait) {
+		if (ret == 0) {
 			wait_on_page_writeback(page);
 			if (PageError(page))
 				ret = -EIO;
-- 
2.13.0

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[PATCH v6 07/20] mm: clean up error handling in write_one_page

[Jeff Layton]

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 | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index b901fe52b153..e369e8ea2a29 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2371,14 +2371,13 @@ 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)
 {
 	struct address_space *mapping = page->mapping;
-	int ret = 0;
+	int ret = 0, ret2;
 	struct writeback_control wbc = {
 		.sync_mode = WB_SYNC_ALL,
 		.nr_to_write = 1,
@@ -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

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[PATCH v6 08/20] lib: add errseq_t type and infrastructure for handling it

[Jeff Layton]

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>
---
 include/linux/errseq.h |  19 +++++
 lib/Makefile           |   2 +-
 lib/errseq.c           | 200 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 220 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/errseq.h
 create mode 100644 lib/errseq.c

diff --git a/include/linux/errseq.h b/include/linux/errseq.h
new file mode 100644
index 000000000000..0d2555f310cd
--- /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;
+
+void __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..d129c0611c1f
--- /dev/null
+++ b/lib/errseq.c
@@ -0,0 +1,200 @@
+#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.
+ */
+void __errseq_set(errseq_t *eseq, int err)
+{
+	errseq_t 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.
+	 */
+	if (WARN(unlikely(err == 0 || (unsigned int)-err > MAX_ERRNO),
+				"err = %d\n", err))
+		return;
+
+	old = READ_ONCE(*eseq);
+	for (;;) {
+		errseq_t new, cur;
+
+		/* 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)
+			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;
+	}
+}
+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 it to the 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

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[PATCH v6 09/20] fs: new infrastructure for writeback error handling and reporting

[Jeff Layton]

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.

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   | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 mm/filemap.c         | 38 +++++++++++++++++++++++++++++++++++++
 6 files changed, 97 insertions(+)

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 803e5a9b2654..e57321b7ee2a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -30,6 +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 +393,7 @@ 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 +848,7 @@ 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;
@@ -2526,6 +2529,56 @@ 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 int __must_check filemap_report_wb_err(struct file *file);
+
+/**
+ * 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)
+{
+	errseq_set(&mapping->wb_err, 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/mm/filemap.c b/mm/filemap.c
index 1de71753de28..aeb58db10688 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -536,6 +536,44 @@ int filemap_write_and_wait_range(struct address_space *mapping,
 EXPORT_SYMBOL(filemap_write_and_wait_range);
 
 /**
+ * filemap_report_wb_err - report wb error (if any) that was previously set
+ * @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 filemap_report_wb_err(struct file *file)
+{
+	int err = 0;
+	struct address_space *mapping = file->f_mapping;
+
+	/* Locklessly handle the common case where nothing has changed */
+	if (errseq_check(&mapping->wb_err, READ_ONCE(file->f_wb_err))) {
+		/* Something changed, must use slow path */
+		spin_lock(&file->f_lock);
+		err = errseq_check_and_advance(&mapping->wb_err,
+						&file->f_wb_err);
+		spin_unlock(&file->f_lock);
+	}
+	return err;
+}
+EXPORT_SYMBOL(filemap_report_wb_err);
+
+/**
  * replace_page_cache_page - replace a pagecache page with a new one
  * @old:	page to be replaced
  * @new:	page to replace with
-- 
2.13.0

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[PATCH v6 10/13] ext4: add more robust reporting of metadata writeback errors

[Jeff Layton]

ext4 uses the blockdev mapping for tracking metadata stored in the
pagecache. Sample its wb_err when opening a file and store that in
the f_md_wb_err field.

Change ext4_sync_file to check for data errors first, and then check the
blockdev mapping for metadata errors afterward.

Note that because metadata writeback errors are only tracked on a
per-device level, this does mean that we'll end up reporting an error on
all open file descriptors when there is a metadata writeback failure.
That's not ideal, but we can possibly improve upon it in the future.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/ext4/dir.c   |  8 ++++++--
 fs/ext4/file.c  |  5 ++++-
 fs/ext4/fsync.c | 13 +++++++++++++
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index e8b365000d73..6bbb19510f74 100644
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -611,9 +611,13 @@ static int ext4_dx_readdir(struct file *file, struct dir_context *ctx)
 
 static int ext4_dir_open(struct inode * inode, struct file * filp)
 {
+	int ret = 0;
+
 	if (ext4_encrypted_inode(inode))
-		return fscrypt_get_encryption_info(inode) ? -EACCES : 0;
-	return 0;
+		ret = fscrypt_get_encryption_info(inode) ? -EACCES : 0;
+	if (!ret)
+		filp->f_md_wb_err = filemap_sample_wb_err(inode->i_sb->s_bdev->bd_inode->i_mapping);
+	return ret;
 }
 
 static int ext4_release_dir(struct inode *inode, struct file *filp)
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 831fd6beebf0..fe0d6e01c4b7 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -435,7 +435,10 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
 		if (ret < 0)
 			return ret;
 	}
-	return dquot_file_open(inode, filp);
+	ret = dquot_file_open(inode, filp);
+	if (!ret)
+		filp->f_md_wb_err = filemap_sample_wb_err(sb->s_bdev->bd_inode->i_mapping);
+	return ret;
 }
 
 /*
diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
index 03d6259d8662..36363a6730d7 100644
--- a/fs/ext4/fsync.c
+++ b/fs/ext4/fsync.c
@@ -165,6 +165,19 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	err = filemap_report_wb_err(file);
 	if (!ret)
 		ret = err;
+
+	/*
+	 * Was there a metadata writeback error since last fsync?
+	 *
+	 * FIXME: ext4 tracks metadata with a whole-block device mapping. So,
+	 * if there is any sort of metadata writeback error, we'll report an
+	 * error on all open fds, even ones not associated with the inode
+	 */
+	err = filemap_report_md_wb_err(file,
+				inode->i_sb->s_bdev->bd_inode->i_mapping);
+	if (!ret)
+		ret = err;
+
 	trace_ext4_sync_file_exit(inode, ret);
 	return ret;
 }
-- 
2.13.0

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[PATCH v6 10/20] mm: tracepoints for writeback error events

[Jeff Layton]

To enable that, make __errseq_set return the value that it was set to
when we exit the loop. Take heed that that value is not suitable as a
later "since" value, as it will not have been marked seen.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 include/linux/errseq.h         |  2 +-
 include/linux/fs.h             |  5 +++-
 include/trace/events/filemap.h | 55 ++++++++++++++++++++++++++++++++++++++++++
 lib/errseq.c                   | 20 ++++++++++-----
 mm/filemap.c                   | 13 +++++++++-
 5 files changed, 86 insertions(+), 9 deletions(-)

diff --git a/include/linux/errseq.h b/include/linux/errseq.h
index 0d2555f310cd..9e0d444ac88d 100644
--- a/include/linux/errseq.h
+++ b/include/linux/errseq.h
@@ -5,7 +5,7 @@
 
 typedef u32	errseq_t;
 
-void __errseq_set(errseq_t *eseq, int err);
+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 */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e57321b7ee2a..6cd87887430b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2530,6 +2530,7 @@ extern int filemap_fdatawrite_range(struct address_space *mapping,
 extern int filemap_check_errors(struct address_space *mapping);
 
 extern int __must_check filemap_report_wb_err(struct file *file);
+extern void __filemap_set_wb_err(struct address_space *mapping, int err);
 
 /**
  * filemap_set_wb_err - set a writeback error on an address_space
@@ -2549,7 +2550,9 @@ extern int __must_check filemap_report_wb_err(struct file *file);
  */
 static inline void filemap_set_wb_err(struct address_space *mapping, int err)
 {
-	errseq_set(&mapping->wb_err, err);
+	/* Fastpath for common case of no error */
+	if (unlikely(err))
+		__filemap_set_wb_err(mapping, err);
 }
 
 /**
diff --git a/include/trace/events/filemap.h b/include/trace/events/filemap.h
index 42febb6bc1d5..2af66920f267 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 +53,60 @@ 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(filemap_report_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/lib/errseq.c b/lib/errseq.c
index d129c0611c1f..009972d3000c 100644
--- a/lib/errseq.c
+++ b/lib/errseq.c
@@ -52,10 +52,14 @@
  *
  * 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.
  */
-void __errseq_set(errseq_t *eseq, int err)
+errseq_t __errseq_set(errseq_t *eseq, int err)
 {
-	errseq_t old;
+	errseq_t cur, old;
 
 	/* MAX_ERRNO must be able to serve as a mask */
 	BUILD_BUG_ON_NOT_POWER_OF_2(MAX_ERRNO + 1);
@@ -66,13 +70,14 @@ void __errseq_set(errseq_t *eseq, int err)
 	 * 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;
+		return old;
 
-	old = READ_ONCE(*eseq);
 	for (;;) {
-		errseq_t new, cur;
+		errseq_t new;
 
 		/* Clear out error bits and set new error */
 		new = (old & ~(MAX_ERRNO|ERRSEQ_SEEN)) | -err;
@@ -82,8 +87,10 @@ void __errseq_set(errseq_t *eseq, int err)
 			new += ERRSEQ_CTR_INC;
 
 		/* If there would be no change, then call it done */
-		if (new == old)
+		if (new == old) {
+			cur = new;
 			break;
+		}
 
 		/* Try to swap the new value into place */
 		cur = cmpxchg(eseq, old, new);
@@ -98,6 +105,7 @@ void __errseq_set(errseq_t *eseq, int err)
 		/* Raced with an update, try again */
 		old = cur;
 	}
+	return cur;
 }
 EXPORT_SYMBOL(__errseq_set);
 
diff --git a/mm/filemap.c b/mm/filemap.c
index aeb58db10688..c5e19ea0bf12 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -535,6 +535,14 @@ 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);
+
 /**
  * filemap_report_wb_err - report wb error (if any) that was previously set
  * @file: struct file on which the error is being reported
@@ -559,14 +567,17 @@ EXPORT_SYMBOL(filemap_write_and_wait_range);
 int filemap_report_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, READ_ONCE(file->f_wb_err))) {
+	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_filemap_report_wb_err(file, old);
 		spin_unlock(&file->f_lock);
 	}
 	return err;
-- 
2.13.0

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[PATCH v6 11/13] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors

[Jeff Layton]

I waxed a little loquacious here, but I figured that more detail was
better, and writeback error handling is so hard to get right.

Although I think we'll eventually remove it once the transition is
complete, I've gone ahead and documented the FS_WB_ERRSEQ flag as well.

Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 Documentation/filesystems/vfs.txt | 50 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 47 insertions(+), 3 deletions(-)

diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index f42b90687d40..c3efdd833a3d 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -576,7 +576,49 @@ 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, expect that error to be
+reported when fsync is called.  After an error has been reported to
+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
+filemap_set_wb_err to record the error in the address_space when it
+occurs.  Then, at the end of their fsync operation, they should call
+filemap_report_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).
+
+Older kernels used a different method for tracking errors, based on flags
+in the address_space. We're currently switching everything over to use
+the infrastructure based on errseq_t values. During the transition,
+filesystem authors will want to also ensure their file_system_type has
+FS_WB_ERRSEQ set in fs_flags to ensure that shared infrastructure is
+aware of the model in use.
 
 struct address_space_operations
 -------------------------------
@@ -804,7 +846,8 @@ 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 +930,8 @@ 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

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[PATCH v6 11/20] mm: set both AS_EIO/AS_ENOSPC and errseq_t in mapping_set_error

[Jeff Layton]

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

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[PATCH v6 12/20] fs: add a new fstype flag to indicate how writeback errors are tracked

[Jeff Layton]

Now that we have new infrastructure for handling writeback errors using
errseq_t, we need to convert the existing code to use it. We could
attempt to retrofit the old interfaces on top of the new, but there is
a conceptual disconnect here in the case of internal callers that
invoke filemap_fdatawait and the like.

When reporting writeback errors, we will always report errors that have
occurred since a particular point in time. With the old writeback error
reporting, the time we used was "since it was last tested/cleared" which
is entirely arbitrary and potentially racy. Now, we can report the
latest error that has occurred since an arbitrary point in time
(represented as a sampled errseq_t value).

This means that we need to touch each filesystem that calls
filemap_check_errors in some fashion and ensure that we establish sane
"since" values for those callers. But...some code is shared between
filesystems and needs to be able to handle both error tracking schemes.

Add a new FS_WB_ERRSEQ flag to the fstype. Later patches will set and
key off of that to decide what behavior should be used.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 include/linux/fs.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6cd87887430b..17ba6284ab14 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2023,6 +2023,7 @@ struct file_system_type {
 #define FS_BINARY_MOUNTDATA	2
 #define FS_HAS_SUBTYPE		4
 #define FS_USERNS_MOUNT		8	/* Can be mounted by userns root */
+#define FS_WB_ERRSEQ		16	/* errseq_t writeback err tracking */
 #define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move() during rename() internally. */
 	struct dentry *(*mount) (struct file_system_type *, int,
 		       const char *, void *);
-- 
2.13.0

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Re: [PATCH v6 12/20] fs: add a new fstype flag to indicate how writeback errors are tracked

[Christoph Hellwig]

On Mon, Jun 12, 2017 at 08:23:06AM -0400, Jeff Layton wrote:
> Add a new FS_WB_ERRSEQ flag to the fstype. Later patches will set and
> key off of that to decide what behavior should be used.

Please invert this so that only file systems that keep the old semantics
need a flag.

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Re: [PATCH v6 12/20] fs: add a new fstype flag to indicate how writeback errors are tracked

[Jeff Layton]

On Mon, 2017-06-12 at 05:45 -0700, Christoph Hellwig wrote:
> On Mon, Jun 12, 2017 at 08:23:06AM -0400, Jeff Layton wrote:
> > Add a new FS_WB_ERRSEQ flag to the fstype. Later patches will set and
> > key off of that to decide what behavior should be used.
> 
> Please invert this so that only file systems that keep the old semantics
> need a flag.


That's definitely what I want for the endgame here. My plan was to add
this flag for now, and then eventually reverse it (or drop it) once all
or most filesystems are converted.

We can do it that way from the get-go if you like. It'll mean tossing in
 a patch add this flag to all filesystems that have an fsync operation
and that use the pagecache, and then gradually remove it from them as we
convert them.

Which method do you prefer?
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Re: [PATCH v6 12/20] fs: add a new fstype flag to indicate how writeback errors are tracked

[Christoph Hellwig]

On Tue, Jun 13, 2017 at 06:24:32AM -0400, Jeff Layton wrote:
> That's definitely what I want for the endgame here. My plan was to add
> this flag for now, and then eventually reverse it (or drop it) once all
> or most filesystems are converted.
> 
> We can do it that way from the get-go if you like. It'll mean tossing in
>  a patch add this flag to all filesystems that have an fsync operation
> and that use the pagecache, and then gradually remove it from them as we
> convert them.
> 
> Which method do you prefer?

Please do it from the get-go.  Or in fact figure out if we can get
away without it entirely.  Moving the error reporting into ->fsync
should help greatly with that, so what's missing after that?

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Re: [PATCH v6 12/20] fs: add a new fstype flag to indicate how writeback errors are tracked

[Jeff Layton]

On Tue, 2017-06-13 at 23:47 -0700, Christoph Hellwig wrote:
> On Tue, Jun 13, 2017 at 06:24:32AM -0400, Jeff Layton wrote:
> > That's definitely what I want for the endgame here. My plan was to add
> > this flag for now, and then eventually reverse it (or drop it) once all
> > or most filesystems are converted.
> > 
> > We can do it that way from the get-go if you like. It'll mean tossing in
> >  a patch add this flag to all filesystems that have an fsync operation
> > and that use the pagecache, and then gradually remove it from them as we
> > convert them.
> > 
> > Which method do you prefer?
> 
> Please do it from the get-go.  Or in fact figure out if we can get
> away without it entirely.  Moving the error reporting into ->fsync
> should help greatly with that, so what's missing after that?

In this smaller set, it's only really used for DAX. In the larger patch
series I have (which needs updating on top of this), there are other
things that key off of it:

sync_file_range: ->fsync isn't called directly there, and I think we
probably want similar semantics to fsync() for it

JBD2: will try to re-set the error after clearing it with
filemap_fdatawait. That's problematic with the new infrastructure so we
need some way to avoid it.

What I think I'll do for now is add a new FS_DAX_WB_ERRSEQ flag that
will go away by the end of the series. As the need arises for a similar
flag in other areas, I'll add them then.

The overall goal is not to need these flags. It may take a bit of time
to get there though.

Thanks for the review so far!
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Re: [PATCH v6 12/20] fs: add a new fstype flag to indicate how writeback errors are tracked

[Christoph Hellwig]

On Wed, Jun 14, 2017 at 01:24:43PM -0400, Jeff Layton wrote:
> In this smaller set, it's only really used for DAX.

DAX only is implemented by three filesystems, please just fix them
up in one go.

> sync_file_range: ->fsync isn't called directly there, and I think we
> probably want similar semantics to fsync() for it

sync_file_range is only supposed to sync data, so it should not call
->fsync.

> JBD2: will try to re-set the error after clearing it with
> filemap_fdatawait. That's problematic with the new infrastructure so we
> need some way to avoid it.

JBD2 only has two users, please fix them up in one go.

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Re: [PATCH v6 12/20] fs: add a new fstype flag to indicate how writeback errors are tracked

[Jeff Layton]

On Thu, 2017-06-15 at 01:22 -0700, Christoph Hellwig wrote:
> On Wed, Jun 14, 2017 at 01:24:43PM -0400, Jeff Layton wrote:
> > In this smaller set, it's only really used for DAX.
> 
> DAX only is implemented by three filesystems, please just fix them
> up in one go.
> 

Ok.

> > sync_file_range: ->fsync isn't called directly there, and I think we
> > probably want similar semantics to fsync() for it
> 
> sync_file_range is only supposed to sync data, so it should not call
> ->fsync.
> 

Correct.

But if there is a data writeback error, should we report an error on all
open fds at that time (like we will for fsync)?

I think we probably do want to do that, but like you say...there is no
file op for sync_file_range. It'll need some way to figure out what sort
of error tracking is in play.

> > JBD2: will try to re-set the error after clearing it with
> > filemap_fdatawait. That's problematic with the new infrastructure so we
> > need some way to avoid it.
> 
> JBD2 only has two users, please fix them up in one go.

I came up with a fix yesterday that makes the flag unnecessary there.

Thanks,
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Re: [PATCH v6 12/20] fs: add a new fstype flag to indicate how writeback errors are tracked

[Christoph Hellwig]

On Thu, Jun 15, 2017 at 06:42:12AM -0400, Jeff Layton wrote:
> Correct.
> 
> But if there is a data writeback error, should we report an error on all
> open fds at that time (like we will for fsync)?

We should in theory, but I don't see how to properly do it.  In addition
sync_file_range just can't be used for data integrity to start with, so
I don't think it's worth it.  At some point we should add a proper
fsync_range syscall, though.

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Re: [PATCH v6 12/20] fs: add a new fstype flag to indicate how writeback errors are tracked

[Jeff Layton]

On Thu, 2017-06-15 at 07:57 -0700, Christoph Hellwig wrote:
> On Thu, Jun 15, 2017 at 06:42:12AM -0400, Jeff Layton wrote:
> > Correct.
> > 
> > But if there is a data writeback error, should we report an error on all
> > open fds at that time (like we will for fsync)?
> 
> We should in theory, but I don't see how to properly do it.  In addition
> sync_file_range just can't be used for data integrity to start with, so
> I don't think it's worth it.  At some point we should add a proper
> fsync_range syscall, though.

filemap_report_wb_err will always return 0 if the inode never has
mapping_set_error called on it. So, I think we should be able to do it
there once we get all of the fs' converted over. That'll have to happen
at the end of the series however.

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[PATCH v6 12/13] xfs: minimal conversion to errseq_t writeback error reporting

[Jeff Layton]

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.

We also set the FS_WB_ERRSEQ flag just for completeness sake.
Not much is really using it at this point.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/xfs/xfs_file.c  | 15 +++++++++++----
 fs/xfs/xfs_super.c |  2 +-
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 5fb5a0958a14..bc3b1575e8db 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -134,7 +134,7 @@ xfs_file_fsync(
 	struct inode		*inode = file->f_mapping->host;
 	struct xfs_inode	*ip = XFS_I(inode);
 	struct xfs_mount	*mp = ip->i_mount;
-	int			error = 0;
+	int			error = 0, err2;
 	int			log_flushed = 0;
 	xfs_lsn_t		lsn = 0;
 
@@ -142,10 +142,12 @@ xfs_file_fsync(
 
 	error = filemap_write_and_wait_range(inode->i_mapping, start, end);
 	if (error)
-		return error;
+		goto out;
 
-	if (XFS_FORCED_SHUTDOWN(mp))
-		return -EIO;
+	if (XFS_FORCED_SHUTDOWN(mp)) {
+		error = -EIO;
+		goto out;
+	}
 
 	xfs_iflags_clear(ip, XFS_ITRUNCATED);
 
@@ -197,6 +199,11 @@ xfs_file_fsync(
 	    mp->m_logdev_targp == mp->m_ddev_targp)
 		xfs_blkdev_issue_flush(mp->m_ddev_targp);
 
+out:
+	err2 = filemap_report_wb_err(file);
+	if (!error)
+		error = err2;
+
 	return error;
 }
 
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 455a575f101d..28d3be187025 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1758,7 +1758,7 @@ static struct file_system_type xfs_fs_type = {
 	.name			= "xfs",
 	.mount			= xfs_fs_mount,
 	.kill_sb		= kill_block_super,
-	.fs_flags		= FS_REQUIRES_DEV,
+	.fs_flags		= FS_REQUIRES_DEV | FS_WB_ERRSEQ,
 };
 MODULE_ALIAS_FS("xfs");
 
-- 
2.13.0

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[PATCH v6 13/13] btrfs: minimal conversion to errseq_t writeback error reporting on fsync

[Jeff Layton]

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..4632f16bc49c 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 = filemap_report_wb_err(file);
+	if (!ret)
+		ret = err;
 	return ret > 0 ? -EIO : ret;
 }
 
-- 
2.13.0

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[PATCH v6 13/20] Documentation: flesh out the section in vfs.txt on storing and reporting writeback errors

[Jeff Layton]

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

Also, although I think we'll eventually remove it once the transition is
complete, I've gone ahead and documented the FS_WB_ERRSEQ flag as well.

Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 Documentation/filesystems/vfs.txt | 48 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 45 insertions(+), 3 deletions(-)

diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index f42b90687d40..0f6415c26385 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -576,7 +576,47 @@ 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, expect that error to be
+reported when fsync is called.  After an error has been reported to
+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 need to do two things:
+
+1) call mapping_set_error to record the error in the address_space when
+one occurs.
+
+2) set FS_WB_ERRSEQ in the fs_flags field in the file_system_type to
+indicate to other subsystems that the filesystem wants to use errseq_t
+based error reporting for writeback.
+
+The flag may go away in the future or moved to an opt-out flag once
+the majority of filesystems are converted to use errseq_t based reporting.
 
 struct address_space_operations
 -------------------------------
@@ -804,7 +844,8 @@ 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 +928,8 @@ 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

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[PATCH v6 14/20] dax: set errors in mapping when writeback fails

[Jeff Layton]

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

-----------------8<-----------------
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.
-----------------8<-----------------

For now, only do this when the FS_WB_ERRSEQ flag is set. The
AS_EIO/AS_ENOSPC flags are not currently cleared in the older code when
writeback initiation fails, only when we discover an error after waiting
on writeback to complete, so we only want to do this with errseq_t based
error handling to prevent seeing duplicate errors on fsync.

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 | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/fs/dax.c b/fs/dax.c
index 2a6889b3585f..ba3b17eefcfc 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -856,8 +856,24 @@ 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) {
+				/*
+				 * For fs' that use errseq_t based error
+				 * tracking, we must call mapping_set_error
+				 * here to ensure that fsync on all open fds
+				 * get back an error. Doing this with the old
+				 * wb error tracking infrastructure is
+				 * problematic though, as DAX writeback is
+				 * synchronous, and the error flags are not
+				 * cleared when initiation fails, only when
+				 * it fails after the write has been submitted
+				 * to the backing store.
+				 */
+				if (mapping->host->i_sb->s_type->fs_flags &
+						FS_WB_ERRSEQ)
+					mapping_set_error(mapping, ret);
 				goto out;
+			}
 		}
 	}
 out:
-- 
2.13.0

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Re: [PATCH v6 14/20] dax: set errors in mapping when writeback fails

[Christoph Hellwig]

On Mon, Jun 12, 2017 at 08:23:10AM -0400, Jeff Layton wrote:
> For now, only do this when the FS_WB_ERRSEQ flag is set. The
> AS_EIO/AS_ENOSPC flags are not currently cleared in the older code when
> writeback initiation fails, only when we discover an error after waiting
> on writeback to complete, so we only want to do this with errseq_t based
> error handling to prevent seeing duplicate errors on fsync.

Please make sure this doens't stay conditional by the end of the series.
We only have three file systems using dax, and a series should be able
to make them agree on a single interface.

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[PATCH v6 15/20] fs: have call_fsync call filemap_report_wb_err if FS_WB_ERRSEQ is set

[Jeff Layton]

Allow filesystems to opt-in to a final check of wb_err if FS_WB_ERRSEQ
is set. Technically, we could just plumb these calls into all of the
fsync operations, but I think this means less code, changes and churn.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 include/linux/fs.h | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 17ba6284ab14..ef3feeec80b2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1742,12 +1742,6 @@ 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,
@@ -2583,6 +2577,20 @@ static inline errseq_t filemap_sample_wb_err(struct address_space *mapping)
 	return errseq_sample(&mapping->wb_err);
 }
 
+static inline int call_fsync(struct file *file, loff_t start, loff_t end,
+			     int datasync)
+{
+	int ret;
+
+	ret = file->f_op->fsync(file, start, end, datasync);
+	if (file->f_mapping->host->i_sb->s_type->fs_flags & FS_WB_ERRSEQ) {
+		int ret2 = filemap_report_wb_err(file);
+		if (!ret)
+			ret = ret2;
+	}
+	return ret;
+}
+
 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);
-- 
2.13.0

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Re: [PATCH v6 15/20] fs: have call_fsync call filemap_report_wb_err if FS_WB_ERRSEQ is set

[Christoph Hellwig]

On Mon, Jun 12, 2017 at 08:23:11AM -0400, Jeff Layton wrote:
> Allow filesystems to opt-in to a final check of wb_err if FS_WB_ERRSEQ
> is set. Technically, we could just plumb these calls into all of the
> fsync operations, but I think this means less code, changes and churn.

Please add it to every fs, that is a consistent with how we handle
everything else related to writeback.

Oh, and please kill this idiotic call_fsync helper while you're at it.

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[PATCH v6 16/20] block: convert to errseq_t based writeback error tracking

[Jeff Layton]

This is a very minimal conversion to errseq_t based error tracking
for raw block device access.

Only real change that is strictly required is that we must ensure that
filemap_report_wb_err is unconditionally called after fsync, which is
now done if FS_WB_ERRSEQ is set in fs_flags. That ensures that the
errseq_t in the file is advanced to the latest value in the mapping.

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 | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 4d62fe771587..4bf865cc99de 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -801,6 +801,7 @@ static struct file_system_type bd_type = {
 	.name		= "bdev",
 	.mount		= bd_mount,
 	.kill_sb	= kill_anon_super,
+	.fs_flags	= FS_WB_ERRSEQ,
 };
 
 struct super_block *blockdev_superblock __read_mostly;
-- 
2.13.0

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[PATCH v6 17/20] fs: add f_md_wb_err field to struct file for tracking metadata errors

[Jeff Layton]

Some filesystems keep a different mapping for metadata writeback. Add a
second errseq_t to struct file for tracking metadata writeback errors.
Also add a new function for checking a mapping of the caller's choosing
vs. the f_md_wb_err value.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 include/linux/fs.h             |  3 +++
 include/trace/events/filemap.h | 23 ++++++++++-------------
 mm/filemap.c                   | 40 +++++++++++++++++++++++++++++++---------
 3 files changed, 44 insertions(+), 22 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index ef3feeec80b2..e366835c93b3 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -871,6 +871,7 @@ struct file {
 	struct list_head	f_tfile_llink;
 #endif /* #ifdef CONFIG_EPOLL */
 	struct address_space	*f_mapping;
+	errseq_t		f_md_wb_err; /* optional metadata wb error tracking */
 } __attribute__((aligned(4)));	/* lest something weird decides that 2 is OK */
 
 struct file_handle {
@@ -2525,6 +2526,8 @@ extern int filemap_fdatawrite_range(struct address_space *mapping,
 extern int filemap_check_errors(struct address_space *mapping);
 
 extern int __must_check filemap_report_wb_err(struct file *file);
+extern int __must_check filemap_report_md_wb_err(struct file *file,
+					struct address_space *mapping);
 extern void __filemap_set_wb_err(struct address_space *mapping, int err);
 
 /**
diff --git a/include/trace/events/filemap.h b/include/trace/events/filemap.h
index 2af66920f267..6e0d78c01a2e 100644
--- a/include/trace/events/filemap.h
+++ b/include/trace/events/filemap.h
@@ -79,12 +79,11 @@ TRACE_EVENT(filemap_set_wb_err,
 );
 
 TRACE_EVENT(filemap_report_wb_err,
-		TP_PROTO(struct file *file, errseq_t old),
+		TP_PROTO(struct address_space *mapping, errseq_t old, errseq_t new),
 
-		TP_ARGS(file, old),
+		TP_ARGS(mapping, old, new),
 
 		TP_STRUCT__entry(
-			__field(struct file *, file);
 			__field(unsigned long, i_ino)
 			__field(dev_t, s_dev)
 			__field(errseq_t, old)
@@ -92,20 +91,18 @@ TRACE_EVENT(filemap_report_wb_err,
 		),
 
 		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;
+			__entry->i_ino = mapping->host->i_ino;
+			if (mapping->host->i_sb)
+				__entry->s_dev = mapping->host->i_sb->s_dev;
 			else
-				__entry->s_dev = file->f_mapping->host->i_rdev;
+				__entry->s_dev = mapping->host->i_rdev;
 			__entry->old = old;
-			__entry->new = file->f_wb_err;
+			__entry->new = new;
 		),
 
-		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)
+		TP_printk("dev=%d:%d ino=0x%lx old=0x%x new=0x%x",
+			MAJOR(__entry->s_dev), MINOR(__entry->s_dev),
+			__entry->i_ino, __entry->old, __entry->new)
 );
 #endif /* _TRACE_FILEMAP_H */
 
diff --git a/mm/filemap.c b/mm/filemap.c
index c5e19ea0bf12..ef0ff6b87759 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -564,27 +564,49 @@ EXPORT_SYMBOL(__filemap_set_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 filemap_report_wb_err(struct file *file)
+static int __filemap_report_wb_err(errseq_t *cursor, spinlock_t *lock,
+				struct address_space *mapping)
 {
 	int err = 0;
-	errseq_t old = READ_ONCE(file->f_wb_err);
-	struct address_space *mapping = file->f_mapping;
+	errseq_t old = READ_ONCE(*cursor);
 
 	/* 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_filemap_report_wb_err(file, old);
-		spin_unlock(&file->f_lock);
+		spin_lock(lock);
+		old = *cursor;
+		err = errseq_check_and_advance(&mapping->wb_err, cursor);
+		trace_filemap_report_wb_err(mapping, old, *cursor);
+		spin_unlock(lock);
 	}
 	return err;
 }
+EXPORT_SYMBOL(__filemap_report_wb_err);
+
+int filemap_report_wb_err(struct file *file)
+{
+	return __filemap_report_wb_err(&file->f_wb_err, &file->f_lock,
+					file->f_mapping);
+}
 EXPORT_SYMBOL(filemap_report_wb_err);
 
 /**
+ * filemap_report_md_wb_err - report wb error (if any) that was previously set
+ * @file: struct file on which the error is being reported
+ * @mapping: pointer to metadata mapping to check
+ *
+ * Many filesystems keep inode metadata in the pagecache, and will use the
+ * cache to write it back to the backing store. This function is for these
+ * callers to track metadata writeback.
+ */
+int filemap_report_md_wb_err(struct file *file, struct address_space *mapping)
+{
+	return __filemap_report_wb_err(&file->f_md_wb_err, &file->f_lock,
+					mapping);
+}
+EXPORT_SYMBOL(filemap_report_md_wb_err);
+
+/**
  * replace_page_cache_page - replace a pagecache page with a new one
  * @old:	page to be replaced
  * @new:	page to replace with
-- 
2.13.0

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[PATCH v6 18/20] ext4: use errseq_t based error handling for reporting data writeback errors

[Jeff Layton]

Add the FS_WB_ERRSEQ flag to indicate to other subsystems that errseq_t
based error reporting for data writeback is in effect, and to opt-in to
reporting those errors in call_fsync.

ext4 uses the blockdev mapping for tracking metadata stored in the
pagecache. Sample its wb_err when opening a file and store that in
the f_md_wb_err field. Ensure that we check and advance the metadata
before returning in fsync.

Note that because metadata writeback errors are only tracked on a
per-device level, this does mean that we'll end up reporting an error on
all open file descriptors on this fs when there is a metadata writeback
failure.  That's not ideal, but we can possibly improve upon it in the
future.

ext4 also has several calls to filemap_fdatawait and
filemap_write_and_wait. Those will also be changed in a later patch to
versions that use errseq_t based reporting.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/ext4/dir.c   |  8 ++++++--
 fs/ext4/file.c  |  5 ++++-
 fs/ext4/fsync.c | 23 +++++++++++++++++++----
 fs/ext4/super.c |  6 +++---
 4 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index e8b365000d73..6bbb19510f74 100644
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -611,9 +611,13 @@ static int ext4_dx_readdir(struct file *file, struct dir_context *ctx)
 
 static int ext4_dir_open(struct inode * inode, struct file * filp)
 {
+	int ret = 0;
+
 	if (ext4_encrypted_inode(inode))
-		return fscrypt_get_encryption_info(inode) ? -EACCES : 0;
-	return 0;
+		ret = fscrypt_get_encryption_info(inode) ? -EACCES : 0;
+	if (!ret)
+		filp->f_md_wb_err = filemap_sample_wb_err(inode->i_sb->s_bdev->bd_inode->i_mapping);
+	return ret;
 }
 
 static int ext4_release_dir(struct inode *inode, struct file *filp)
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 02ce7e7bbdf5..6e505269132c 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -435,7 +435,10 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
 		if (ret < 0)
 			return ret;
 	}
-	return dquot_file_open(inode, filp);
+	ret = dquot_file_open(inode, filp);
+	if (!ret)
+		filp->f_md_wb_err = filemap_sample_wb_err(sb->s_bdev->bd_inode->i_mapping);
+	return ret;
 }
 
 /*
diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
index 9d549608fd30..09e28b7fd3f6 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);
 
@@ -126,7 +128,8 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 
 	ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
 	if (ret)
-		return ret;
+		goto out;
+
 	/*
 	 * data=writeback,ordered:
 	 *  The caller's filemap_fdatawrite()/wait will sync the data.
@@ -152,12 +155,24 @@ 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;
 	}
 out:
+	/*
+	 * Was there a metadata writeback error since last fsync?
+	 *
+	 * FIXME: ext4 tracks metadata with a whole-block device mapping. So,
+	 * if there is any sort of metadata writeback error, we'll report an
+	 * error on all open fds, even ones not associated with the inode
+	 */
+	err = filemap_report_md_wb_err(file,
+				inode->i_sb->s_bdev->bd_inode->i_mapping);
+	if (!ret)
+		ret = err;
+
 	trace_ext4_sync_file_exit(inode, ret);
 	return ret;
 }
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d37c81f327e7..e98791ebee6f 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -119,7 +119,7 @@ static struct file_system_type ext2_fs_type = {
 	.name		= "ext2",
 	.mount		= ext4_mount,
 	.kill_sb	= kill_block_super,
-	.fs_flags	= FS_REQUIRES_DEV,
+	.fs_flags	= FS_REQUIRES_DEV|FS_WB_ERRSEQ,
 };
 MODULE_ALIAS_FS("ext2");
 MODULE_ALIAS("ext2");
@@ -134,7 +134,7 @@ static struct file_system_type ext3_fs_type = {
 	.name		= "ext3",
 	.mount		= ext4_mount,
 	.kill_sb	= kill_block_super,
-	.fs_flags	= FS_REQUIRES_DEV,
+	.fs_flags	= FS_REQUIRES_DEV|FS_WB_ERRSEQ,
 };
 MODULE_ALIAS_FS("ext3");
 MODULE_ALIAS("ext3");
@@ -5689,7 +5689,7 @@ static struct file_system_type ext4_fs_type = {
 	.name		= "ext4",
 	.mount		= ext4_mount,
 	.kill_sb	= kill_block_super,
-	.fs_flags	= FS_REQUIRES_DEV,
+	.fs_flags	= FS_REQUIRES_DEV|FS_WB_ERRSEQ,
 };
 MODULE_ALIAS_FS("ext4");
 
-- 
2.13.0

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[PATCH v6 19/20] xfs: minimal conversion to errseq_t writeback error reporting

[Jeff Layton]

Just set the FS_WB_ERRSEQ flag to indicate that we want to use errseq_t
based error reporting. Internal filemap_* calls are left as-is for now.

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

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 455a575f101d..28d3be187025 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1758,7 +1758,7 @@ static struct file_system_type xfs_fs_type = {
 	.name			= "xfs",
 	.mount			= xfs_fs_mount,
 	.kill_sb		= kill_block_super,
-	.fs_flags		= FS_REQUIRES_DEV,
+	.fs_flags		= FS_REQUIRES_DEV | FS_WB_ERRSEQ,
 };
 MODULE_ALIAS_FS("xfs");
 
-- 
2.13.0

Re: [PATCH v6 19/20] xfs: minimal conversion to errseq_t writeback error reporting

[Darrick J. Wong]

On Mon, Jun 12, 2017 at 08:23:15AM -0400, Jeff Layton wrote:
> Just set the FS_WB_ERRSEQ flag to indicate that we want to use errseq_t
> based error reporting. Internal filemap_* calls are left as-is for now.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  fs/xfs/xfs_super.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 455a575f101d..28d3be187025 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -1758,7 +1758,7 @@ static struct file_system_type xfs_fs_type = {
>  	.name			= "xfs",
>  	.mount			= xfs_fs_mount,
>  	.kill_sb		= kill_block_super,
> -	.fs_flags		= FS_REQUIRES_DEV,
> +	.fs_flags		= FS_REQUIRES_DEV | FS_WB_ERRSEQ,

Huh?  Why are there two patches with the same subject line?  And this
same bit of code too?  Or ... 11/13, 11/20?  What's going on here?

<confused>

--D

>  };
>  MODULE_ALIAS_FS("xfs");
>  
> -- 
> 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

Re: [PATCH v6 19/20] xfs: minimal conversion to errseq_t writeback error reporting

[Jeff Layton]

On Mon, 2017-06-12 at 21:30 -0700, Darrick J. Wong wrote:
> On Mon, Jun 12, 2017 at 08:23:15AM -0400, Jeff Layton wrote:
> > Just set the FS_WB_ERRSEQ flag to indicate that we want to use errseq_t
> > based error reporting. Internal filemap_* calls are left as-is for now.
> > 
> > Signed-off-by: Jeff Layton <jlayton@redhat.com>
> > ---
> >  fs/xfs/xfs_super.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> > index 455a575f101d..28d3be187025 100644
> > --- a/fs/xfs/xfs_super.c
> > +++ b/fs/xfs/xfs_super.c
> > @@ -1758,7 +1758,7 @@ static struct file_system_type xfs_fs_type = {
> >  	.name			= "xfs",
> >  	.mount			= xfs_fs_mount,
> >  	.kill_sb		= kill_block_super,
> > -	.fs_flags		= FS_REQUIRES_DEV,
> > +	.fs_flags		= FS_REQUIRES_DEV | FS_WB_ERRSEQ,
> 
> Huh?  Why are there two patches with the same subject line?  And this
> same bit of code too?  Or ... 11/13, 11/20?  What's going on here?
> 
> <confused>
> 
> --D

Oh my -- sorry about that. I ended up with two different interleaved
patchsets. The /20 series is the one I meant to send.

Just ignore these for now though, as I'll be sending a v7 (at least) to
address HCH's comments.
-- 
Jeff Layton <jlayton@redhat.com>

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[PATCH v6 20/20] btrfs: minimal conversion to errseq_t writeback error reporting on fsync

[Jeff Layton]

Set the FS_WB_ERRSEQ flag to opt-in to errseq_t based reporting.
Internal call to filemap_* functions are left as-is.

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

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 4f1cdd5058f1..c99af09cd3e7 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2184,7 +2184,7 @@ static struct file_system_type btrfs_fs_type = {
 	.name		= "btrfs",
 	.mount		= btrfs_mount,
 	.kill_sb	= btrfs_kill_super,
-	.fs_flags	= FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA,
+	.fs_flags	= FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA | FS_WB_ERRSEQ,
 };
 MODULE_ALIAS_FS("btrfs");
 
-- 
2.13.0

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