Commit 06bd3c36a733 (ext4: fix data exposure after a crash) uncovered a
deadlock in ext4_writepages() which was previously much harder to hit.
After this commit xfstest generic/130 reproduces the deadlock on small
filesystems.
The problem happens when ext4_do_update_inode() sets LARGE_FILE feature
and marks current inode handle as synchronous. That subsequently results
in ext4_journal_stop() called from ext4_writepages() to block waiting for
transaction commit while still holding page locks, reference to io_end,
and some prepared bio in mpd structure each of which can possibly block
transaction commit from completing and thus results in deadlock.
Fix the problem by releasing page locks, io_end reference, and
submitting prepared bio before calling ext4_journal_stop().
Reported-and-tested-by: Eryu Guan <eguan@xxxxxxxxxx>
CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/ext4/inode.c | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index f7140ca66e3b..ba04d57656d4 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2748,13 +2748,27 @@ retry:
done = true;
}
}
- ext4_journal_stop(handle);
/* Submit prepared bio */
ext4_io_submit(&mpd.io_submit);
/* Unlock pages we didn't use */
mpage_release_unused_pages(&mpd, give_up_on_write);
- /* Drop our io_end reference we got from init */
- ext4_put_io_end(mpd.io_submit.io_end);
+ /*
+ * Drop our io_end reference we got from init. We have to be
+ * careful and use deferred io_end finishing as we can release
+ * the last reference to io_end which may end up doing unwritten
+ * extent conversion which we cannot do while holding
+ * transaction handle.
+ */
+ ext4_put_io_end_defer(mpd.io_submit.io_end);
+ /*
+ * Caution: ext4_journal_stop() can wait for transaction commit
+ * to finish which may depend on writeback of pages to complete
+ * or on page lock to be released. So we can call it only
+ * after we have submitted all the IO, released page locks
+ * we hold, and dropped io_end reference (for extent conversion
+ * to be able to complete).
+ */
+ ext4_journal_stop(handle);
if (ret == -ENOSPC && sbi->s_journal) {
/*
--
2.6.6
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