[Ocfs2-devel] [PATCH RFC V1 1/1] ocfs2: fix a deadlock caused by commit 6f1b228529ae49b0

[Gautham Ananthakrishna via Ocfs2-devel <ocfs2-devel@oss.oracle.com>]

commit 6f1b228529ae49b0f85ab89bcdb6c365df401558 caused a deadlock
which was uncovered by our internal tests. The deadlock is as foollows:

Task 1:
A1) jbd2_journal_commit_transaction()
A2)         spin_lock(&jh->b_state_lock);
A3)         __jbd2_journal_remove_checkpoint()
A4)                         jbd2_journal_put_journal_head()
A5)                                         jbd_lock_bh_journal_head()

Task 2:
B1) ocfs2_test_bg_bit_allocatable()
B2)         jbd_lock_bh_journal_head()
B3)         spin_lock(&jh->b_state_lock);

A1->A2->A3->A4->B1->B2->B3(blocked)->A5(blocked)

Now cause process 2 has the jbd lock, it doesn’t let process 1 to continue after A5.
Process 2 now is waiting for b_state_lock to be released by process 1.

This patch resolves the deadlock.

Signed-off-by: Gautham Ananthakrishna <gautham.ananthakrishna@oracle.com>
---
 fs/ocfs2/suballoc.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
index 481017e..a618970 100644
--- a/fs/ocfs2/suballoc.c
+++ b/fs/ocfs2/suballoc.c
@@ -1259,9 +1259,8 @@ static int ocfs2_test_bg_bit_allocatable(struct buffer_head *bg_bh,
 	if (!buffer_jbd(bg_bh))
 		return 1;
 
-	jbd_lock_bh_journal_head(bg_bh);
-	if (buffer_jbd(bg_bh)) {
-		jh = bh2jh(bg_bh);
+	jh = jbd2_journal_grab_journal_head(bg_bh);
+	if (jh) {
 		spin_lock(&jh->b_state_lock);
 		bg = (struct ocfs2_group_desc *) jh->b_committed_data;
 		if (bg)
@@ -1269,8 +1268,8 @@ static int ocfs2_test_bg_bit_allocatable(struct buffer_head *bg_bh,
 		else
 			ret = 1;
 		spin_unlock(&jh->b_state_lock);
+		jbd2_journal_put_journal_head(bg_bh);
 	}
-	jbd_unlock_bh_journal_head(bg_bh);
 
 	return ret;
 }
-- 
1.8.3.1


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