ocfs2: fix race between searching chunks and release journal_head from buffer_head

Encountered a race between ocfs2_test_bg_bit_allocatable() and
jbd2_journal_put_journal_head() resulting in the below vmcore.

  PID: 106879  TASK: ffff880244ba9c00  CPU: 2   COMMAND: "loop3"
  Call trace:
    panic
    oops_end
    no_context
    __bad_area_nosemaphore
    bad_area_nosemaphore
    __do_page_fault
    do_page_fault
    page_fault
      [exception RIP: ocfs2_block_group_find_clear_bits+316]
    ocfs2_block_group_find_clear_bits [ocfs2]
    ocfs2_cluster_group_search [ocfs2]
    ocfs2_search_chain [ocfs2]
    ocfs2_claim_suballoc_bits [ocfs2]
    __ocfs2_claim_clusters [ocfs2]
    ocfs2_claim_clusters [ocfs2]
    ocfs2_local_alloc_slide_window [ocfs2]
    ocfs2_reserve_local_alloc_bits [ocfs2]
    ocfs2_reserve_clusters_with_limit [ocfs2]
    ocfs2_reserve_clusters [ocfs2]
    ocfs2_lock_refcount_allocators [ocfs2]
    ocfs2_make_clusters_writable [ocfs2]
    ocfs2_replace_cow [ocfs2]
    ocfs2_refcount_cow [ocfs2]
    ocfs2_file_write_iter [ocfs2]
    lo_rw_aio
    loop_queue_work
    kthread_worker_fn
    kthread
    ret_from_fork

When ocfs2_test_bg_bit_allocatable() called bh2jh(bg_bh), the
bg_bh->b_private NULL as jbd2_journal_put_journal_head() raced and
released the jounal head from the buffer head.  Needed to take bit lock
for the bit 'BH_JournalHead' to fix this race.

Link: https://lkml.kernel.org/r/1634820718-6043-1-git-send-email-gautham.ananthakrishna@oracle.com
Signed-off-by: Gautham Ananthakrishna <[email protected]>
Reviewed-by: Joseph Qi <[email protected]>
Cc: <[email protected]>
Cc: Mark Fasheh <[email protected]>
Cc: Joel Becker <[email protected]>
Cc: Junxiao Bi <[email protected]>
Cc: Changwei Ge <[email protected]>
Cc: Gang He <[email protected]>
Cc: Jun Piao <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: gtmoth

fs/ocfs2/suballoc.c

@@ -1251,22 +1251,26 @@ 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;
+	int ret = 1;
 
 	if (ocfs2_test_bit(nr, (unsigned long *)bg->bg_bitmap))
 		return 0;
 
 	if (!buffer_jbd(bg_bh))
 		return 1;
 
-	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_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);
 
 	return ret;
 }