[PATCH 12/19] ext4: check for a metadata write error with buffer_write_io_error()

[Chao Shi <coshi036@gmail.com>]

Two places detect a failed metadata write by testing !buffer_uptodate()
after waiting for it.  That relies on the write completion handler clearing
BH_Uptodate on error, which this series removes: a buffer whose write
failed still holds the data the filesystem asked to be written, so
declaring it not up to date is wrong and makes callers re-read it.

ext4 already does this correctly for the superblock - see
ext4_commit_super(), which tests buffer_write_io_error() - so this brings
the other two into line.

In __ext4_handle_dirty_metadata() the old test also required BH_Req.
BH_Write_EIO implies it, so the pair collapses into one test.  The new test
is also strictly stronger than consuming sync_dirty_buffer()'s return
value, because it still fires when the buffer was written by background
writeback and that write hit an error, which sync_dirty_buffer() does not
report.

Note that BH_Write_EIO stays set until the buffer is written again,
forgotten or invalidated, so an unrepaired itable block now reports on
every subsequent sync of that inode rather than only on the write that
failed.  That is the intended behaviour and matches what ocfs2 has always
done with this flag.

No behaviour change today - a failed write sets BH_Write_EIO and clears
BH_Uptodate together.  It stops being a no-op at the end of the series,
where the new test is the one that still works.

Signed-off-by: Chao Shi <coshi036@gmail.com>
---
 fs/ext4/ext4_jbd2.c | 2 +-
 fs/ext4/mmp.c       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
index 02b066299164..f338d6e3c29f 100644
--- a/fs/ext4/ext4_jbd2.c
+++ b/fs/ext4/ext4_jbd2.c
@@ -413,7 +413,7 @@ int __ext4_handle_dirty_metadata(const char *where, unsigned int line,
 		}
 		if (inode && inode_needs_sync(inode)) {
 			sync_dirty_buffer(bh);
-			if (buffer_req(bh) && !buffer_uptodate(bh)) {
+			if (buffer_write_io_error(bh)) {
 				ext4_error_inode_err(inode, where, line,
 						     bh->b_blocknr, EIO,
 					"IO error syncing itable block");
diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
index 7ce361484b38..4b18ddef468d 100644
--- a/fs/ext4/mmp.c
+++ b/fs/ext4/mmp.c
@@ -49,7 +49,7 @@ static int write_mmp_block_thawed(struct super_block *sb,
 	bh_submit(bh, REQ_OP_WRITE | REQ_SYNC | REQ_META | REQ_PRIO,
 			bh_end_write);
 	wait_on_buffer(bh);
-	if (unlikely(!buffer_uptodate(bh)))
+	if (unlikely(buffer_write_io_error(bh)))
 		return -EIO;
 	return 0;
 }
-- 
2.43.0