[PATCH v2] Btrfs: add another missing end_page_writeback on submit_extent_page failure

From: Takafumi Kubota
Date: Thu Feb 09 2017 - 04:33:20 EST

If btrfs_bio_alloc fails in submit_extent_page, submit_extent_page returns
without clearing the writeback bit of the failed page.

__extent_writepage_io, that is a caller of submit_extent_page,
does not clear the remaining writeback bit anywhere.
As a result, this will cause the hang at filemap_fdatawait_range,
because it waits the writeback bit to be cleared from the failed page.
So, we have to call end_page_writeback to clear the writeback bit.

For reproducing the hang, we inject a fault like

if (should_failtest()) { // I define should_failtest()
bio = NULL;
else {
bio = btrfs_bio_alloc(...);

in submit_extent_page.

We should also check whether page has the bit before end_page_writeback,
to avoid the conflict against the other end_page_writeback in bio_endio.
Thus, we add PageWriteback checks not only in __extent_writepage_io,
but also in write_one_eb too, because it misses the check.

Signed-off-by: Takafumi Kubota <takafumi.kubota1012@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
Cc: David Sterba <dsterba@xxxxxxx>
fs/btrfs/extent_io.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 4ac383a..aa1908a 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3445,8 +3445,11 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode,
bdev, &epd->bio, max_nr,
0, 0, 0, false);
- if (ret)
+ if (ret) {
+ if (PageWriteback(page))
+ end_page_writeback(page);
+ }

cur = cur + iosize;
pg_offset += iosize;
@@ -3767,7 +3770,8 @@ static noinline_for_stack int write_one_eb(struct extent_buffer *eb,
epd->bio_flags = bio_flags;
if (ret) {
- end_page_writeback(p);
+ if (PageWriteback(p))
+ end_page_writeback(p);
if (atomic_sub_and_test(num_pages - i, &eb->io_pages))
ret = -EIO;