[PATCH 06/19] buffer: detect metadata write errors with buffer_write_io_error()

[Chao Shi]

Both places in this file that report a metadata write error to a caller do
it by testing !buffer_uptodate() after waiting for the write.  That works
only because the write completion handlers clear BH_Uptodate when the write
fails, which is what this series is removing: a buffer whose write failed
still holds the correct data, and saying otherwise makes callers rewrite,
re-read or WARN over a buffer that was never wrong.

BH_Write_EIO is the flag that actually means "the last write of this buffer
failed", and both handlers already set it via mark_buffer_write_io_error().
Test that instead.

No behaviour change: today a failed write through bh_end_write() or
bh_end_async_write() sets BH_Write_EIO and clears BH_Uptodate together, so
the two tests agree.  They stop agreeing at the end of the series, and this
one stays right.

In __sync_dirty_buffer() the flag also refers unambiguously to the write we
just issued, because __bh_submit() clears it when it resubmits a buffer for
write.

Signed-off-by: Chao Shi <coshi036@xxxxxxxxx>
---
 fs/buffer.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 50a63d964815..ac978d9090c2 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -618,7 +618,7 @@ int mmb_sync(struct mapping_metadata_bhs *mmb)
 		}
 		spin_unlock(&mmb->lock);
 		wait_on_buffer(bh);
-		if (!buffer_uptodate(bh))
+		if (buffer_write_io_error(bh))
 			err = -EIO;
 		brelse(bh);
 		spin_lock(&mmb->lock);
@@ -2743,7 +2743,7 @@ int __sync_dirty_buffer(struct buffer_head *bh, blk_opf_t op_flags)
 
 		bh_submit(bh, REQ_OP_WRITE | op_flags, bh_end_write);
 		wait_on_buffer(bh);
-		if (!buffer_uptodate(bh))
+		if (buffer_write_io_error(bh))
 			return -EIO;
 	} else {
 		unlock_buffer(bh);
-- 
2.43.0