[PATCH] jbd2: fix deadlock in jbd2_journal_cancel_revoke()

[Zhang Yi]

From: Zhang Yi <yi.zhang@xxxxxxxxxx>

Commit f76d4c28a46a ("fs/jbd2: use sleeping version of
__find_get_block()") changed jbd2_journal_cancel_revoke() to use
__find_get_block_nonatomic() which holds the folio lock instead of
i_private_lock. This breaks the lock ordering (folio -> buffer) and
causes an ABBA deadlock when the filesystem blocksize < pagesize:

     T1                                T2
ext4_mkdir()
 ext4_init_new_dir()
  ext4_append()
   ext4_getblk()
    lock_buffer()    <- A
                                   sync_blockdev()
                                    blkdev_writepages()
                                     writeback_iter()
                                      writeback_get_folio()
                                       folio_lock()   <- B
     ext4_journal_get_create_access()
      jbd2_journal_cancel_revoke()
       __find_get_block_nonatomic()
        folio_lock()  <- B
                                     block_write_full_folio()
                                      lock_buffer()   <- A

This can occasionally cause generic/013 to hang.

Fix by only calling __find_get_block_nonatomic() when the passed
buffer_head doesn't belong to the bdev (i.e., !bh->b_bdev), which is the
only case that we need to look up its bdev alias. Otherwise, the lookup
is redundant since the found buffer_head is equal to the one we passed
in.

Fixes: f76d4c28a46a ("fs/jbd2: use sleeping version of __find_get_block()")
Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
---
 fs/jbd2/revoke.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/jbd2/revoke.c b/fs/jbd2/revoke.c
index 9016ddb82447..8b52d40c27c9 100644
--- a/fs/jbd2/revoke.c
+++ b/fs/jbd2/revoke.c
@@ -464,13 +464,14 @@ void jbd2_journal_cancel_revoke(handle_t *handle, struct journal_head *jh)
 	 * buffer_head?  If so, we'd better make sure we clear the
 	 * revoked status on any hashed alias too, otherwise the revoke
 	 * state machine will get very upset later on. */
-	if (need_cancel) {
+	if (need_cancel && !bh->b_bdev) {
 		struct buffer_head *bh2;
+
 		bh2 = __find_get_block_nonatomic(bh->b_bdev, bh->b_blocknr,
 						 bh->b_size);
 		if (bh2) {
-			if (bh2 != bh)
-				clear_buffer_revoked(bh2);
+			WARN_ON_ONCE(bh2 == bh);
+			clear_buffer_revoked(bh2);
 			__brelse(bh2);
 		}
 	}
-- 
2.52.0