[PATCH 15/19] gfs2: check for a metadata write error with buffer_write_io_error()

[Chao Shi <coshi036@gmail.com>]

gfs2_ail1_start_one() and gfs2_ail1_empty_one() decide whether a buffer on
the ail reached the disk by looking at BH_Uptodate once it is no longer
busy.  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.  Test BH_Write_EIO instead.  In
gfs2_ail1_start_one() the test is the positive one, so the sense has to be
inverted rather than the flag simply swapped.

This is not a pure conversion for gfs2, because gfs2 already has a private
write completion handler that behaves the way this series is heading:
gfs2_end_log_write_bh() calls mark_buffer_write_io_error() and leaves
BH_Uptodate alone.  Buffers completed through it are therefore invisible to
both tests today, and start being caught once they look at BH_Write_EIO.
That is a real behaviour change, and it is the one gfs2 wanted: a failed
log write now withdraws the filesystem instead of passing silently.

gfs2_pin() is a different case and gets a different treatment.  Its
!buffer_uptodate() test is not only a proxy for a failed write - a buffer
with no valid contents at all is equally a reason to withdraw before
pinning it into a transaction - so the write error test is added to it
rather than replacing it.

Left alone deliberately: the BUG_ON(!buffer_uptodate(bh)) in gfs2_unpin()
and the two WARN_ON()s in fs/gfs2/rgrp.c.  After this series they simply
stop firing for write errors, which is correct; turning them into
BUG_ON(buffer_write_io_error(bh)) would newly panic on an I/O error.

Signed-off-by: Chao Shi <coshi036@gmail.com>
---
 fs/gfs2/log.c  | 4 ++--
 fs/gfs2/lops.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 78bba8cc10b8..e3e0dcb1f567 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -107,7 +107,7 @@ __acquires(&sdp->sd_ail_lock)
 		gfs2_assert(sdp, bd->bd_tr == tr);
 
 		if (!buffer_busy(bh)) {
-			if (buffer_uptodate(bh)) {
+			if (!buffer_write_io_error(bh)) {
 				list_move(&bd->bd_ail_st_list,
 					  &tr->tr_ail2_list);
 				continue;
@@ -321,7 +321,7 @@ static int gfs2_ail1_empty_one(struct gfs2_sbd *sdp, struct gfs2_trans *tr,
 			active_count++;
 			continue;
 		}
-		if (!buffer_uptodate(bh) &&
+		if (buffer_write_io_error(bh) &&
 		    !cmpxchg(&sdp->sd_log_error, 0, -EIO))
 			gfs2_io_error_bh(sdp, bh);
 		/*
diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index 6dabe73ad790..3df6e4b7e8b9 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -48,7 +48,7 @@ void gfs2_pin(struct gfs2_sbd *sdp, struct buffer_head *bh)
 	clear_buffer_dirty(bh);
 	if (test_set_buffer_pinned(bh))
 		gfs2_assert_withdraw(sdp, 0);
-	if (!buffer_uptodate(bh))
+	if (!buffer_uptodate(bh) || buffer_write_io_error(bh))
 		gfs2_io_error_bh(sdp, bh);
 	bd = bh->b_private;
 	/* If this buffer is in the AIL and it has already been written
-- 
2.43.0