[PATCH 2/2] ocfs2: fix a deadlock when commit trans

[Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>]

commit 6f1b228529ae introduces a regression which can deadlock as
follows:

Task1:                              Task2:
jbd2_journal_commit_transaction     ocfs2_test_bg_bit_allocatable
spin_lock(&jh->b_state_lock)        jbd_lock_bh_journal_head
__jbd2_journal_remove_checkpoint    spin_lock(&jh->b_state_lock)
jbd2_journal_put_journal_head
jbd_lock_bh_journal_head

Task1 and Task2 lock bh->b_state and jh->b_state_lock in different
order, which finally result in a deadlock.

So use jbd2_journal_[grab|put]_journal_head instead in
ocfs2_test_bg_bit_allocatable() to fix it.

Reported-by: Gautham Ananthakrishna <gautham.ananthakrishna@xxxxxxxxxx>
Fixes: 6f1b228529ae ("ocfs2: fix race between searching chunks and release journal_head from buffer_head")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
---
 fs/ocfs2/suballoc.c | 25 +++++++++++--------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
index 481017e1dac5..166c8918c825 100644
--- a/fs/ocfs2/suballoc.c
+++ b/fs/ocfs2/suballoc.c
@@ -1251,26 +1251,23 @@ static int ocfs2_test_bg_bit_allocatable(struct buffer_head *bg_bh,
 {
 	struct ocfs2_group_desc *bg = (struct ocfs2_group_desc *) bg_bh->b_data;
 	struct journal_head *jh;
-	int ret = 1;
+	int ret;
 
 	if (ocfs2_test_bit(nr, (unsigned long *)bg->bg_bitmap))
 		return 0;
 
-	if (!buffer_jbd(bg_bh))
+	jh = jbd2_journal_grab_journal_head(bg_bh);
+	if (!jh)
 		return 1;
 
-	jbd_lock_bh_journal_head(bg_bh);
-	if (buffer_jbd(bg_bh)) {
-		jh = bh2jh(bg_bh);
-		spin_lock(&jh->b_state_lock);
-		bg = (struct ocfs2_group_desc *) jh->b_committed_data;
-		if (bg)
-			ret = !ocfs2_test_bit(nr, (unsigned long *)bg->bg_bitmap);
-		else
-			ret = 1;
-		spin_unlock(&jh->b_state_lock);
-	}
-	jbd_unlock_bh_journal_head(bg_bh);
+	spin_lock(&jh->b_state_lock);
+	bg = (struct ocfs2_group_desc *) jh->b_committed_data;
+	if (bg)
+		ret = !ocfs2_test_bit(nr, (unsigned long *)bg->bg_bitmap);
+	else
+		ret = 1;
+	spin_unlock(&jh->b_state_lock);
+	jbd2_journal_put_journal_head(jh);
 
 	return ret;
 }
-- 
2.19.1.6.gb485710b