jbd2: fix potential buffer head reference count leak

As in 'jbd2_fc_wait_bufs' if buffer isn't uptodate, will return -EIO without
update 'journal->j_fc_off'. But 'jbd2_fc_release_bufs' will release buffer head
from ‘j_fc_off - 1’ if 'bh' is NULL will terminal release which will lead to
buffer head buffer head reference count leak.
To solve above issue, update 'journal->j_fc_off' before return -EIO.

Cc: stable@kernel.org
Signed-off-by: Ye Bin <yebin10@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220914100812.1414768-2-yebin10@huawei.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/jbd2/journal.c

@@ -925,8 +925,14 @@ int jbd2_fc_wait_bufs(journal_t *journal, int num_blks)
 		wait_on_buffer(bh);
 		put_bh(bh);
 		journal->j_fc_wbuf[i] = NULL;
-		if (unlikely(!buffer_uptodate(bh)))
+		/*
+		 * Update j_fc_off so jbd2_fc_release_bufs can release remain
+		 * buffer head.
+		 */
+		if (unlikely(!buffer_uptodate(bh))) {
+			journal->j_fc_off = i;
 			return -EIO;
+		}
 	}
 
 	return 0;