[PATCH v2 17/21] jbd2: report journal write errors with BH_Write_EIO

[Chao Shi <coshi036@gmail.com>]

The journal's own write completion handler,
journal_end_buffer_io_sync(), reports a failed write by clearing
BH_Uptodate, and the three places that wait for journal writes look for
that.  This series is removing that convention: a buffer whose write failed
still holds the data that was supposed to reach the disk, and saying it is
not up to date makes callers rewrite, re-read or WARN over data that was
never wrong.

Set BH_Write_EIO instead, with mark_buffer_write_io_error(), and test it in
journal_wait_on_commit_record() and in the two commit-phase waits.

The handler stops touching BH_Uptodate in either direction.  Setting it on
success was never needed: every caller marks the buffer up to date before
submitting the write, because a buffer with no valid data is not something
you can write out.  The local flag is renamed to match what it now means.

The two changes have to go together, because commit phase 4 waits on a
mixed list: descriptor blocks are submitted with
journal_end_buffer_io_sync(), while revoke blocks go through
write_dirty_buffer() and land in bh_end_write().  bh_end_write() already
sets BH_Write_EIO, so converting the consumer alone would keep working for
revoke blocks and silently stop detecting failed descriptor writes.  With
the handler converted, both halves of the list report the same way.

mark_buffer_write_io_error() is safe on all of these buffers.  The shadow
buffers from jbd2_journal_write_metadata_buffer() have no folio and no
associated mapping, so it does nothing beyond setting the flag.  Descriptor
and commit blocks are ordinary buffers on the journal device, and marking
the journal's mapping with the error is what write_dirty_buffer() already
does for revoke blocks on the same device.

Acked-by: Weidong Zhu <weizhu@fiu.edu>
Signed-off-by: Chao Shi <coshi036@gmail.com>
---
 fs/jbd2/commit.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 0c85af91f9b2..cd7ef783bd36 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -32,14 +32,12 @@
 static void journal_end_buffer_io_sync(struct bio *bio)
 {
 	struct buffer_head *bh;
-	bool uptodate = bio_endio_bh(bio, &bh);
+	bool success = bio_endio_bh(bio, &bh);
 	struct buffer_head *orig_bh = bh->b_private;
 
 	BUFFER_TRACE(bh, "");
-	if (uptodate)
-		set_buffer_uptodate(bh);
-	else
-		clear_buffer_uptodate(bh);
+	if (!success)
+		mark_buffer_write_io_error(bh);
 	if (orig_bh) {
 		clear_and_wake_up_bit(BH_Shadow, &orig_bh->b_state);
 	}
@@ -169,7 +167,7 @@ static int journal_wait_on_commit_record(journal_t *journal,
 	clear_buffer_dirty(bh);
 	wait_on_buffer(bh);
 
-	if (unlikely(!buffer_uptodate(bh)))
+	if (unlikely(buffer_write_io_error(bh)))
 		ret = -EIO;
 	put_bh(bh);            /* One for getblk() */
 
@@ -834,7 +832,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 		wait_on_buffer(bh);
 		cond_resched();
 
-		if (unlikely(!buffer_uptodate(bh)))
+		if (unlikely(buffer_write_io_error(bh)))
 			err = -EIO;
 		jbd2_unfile_log_bh(bh);
 		stats.run.rs_blocks_logged++;
@@ -877,7 +875,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 		wait_on_buffer(bh);
 		cond_resched();
 
-		if (unlikely(!buffer_uptodate(bh)))
+		if (unlikely(buffer_write_io_error(bh)))
 			err = -EIO;
 
 		BUFFER_TRACE(bh, "ph5: control buffer writeout done: unfile");
-- 
2.43.0