[PATCH 4.9 046/159] fs: dlm: fix race between test_bit() and queue_work()

[Greg Kroah-Hartman]

From: Alexander Aring <aahringo@xxxxxxxxxx>

commit eef6ec9bf390e836a6c4029f3620fe49528aa1fe upstream.

This patch fixes a race by using ls_cb_mutex around the bit
operations and conditional code blocks for LSFL_CB_DELAY.

The function dlm_callback_stop() expects to stop all callbacks and
flush all currently queued onces. The set_bit() is not enough because
there can still be queue_work() after the workqueue was flushed.
To avoid queue_work() after set_bit(), surround both by ls_cb_mutex.

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Alexander Aring <aahringo@xxxxxxxxxx>
Signed-off-by: David Teigland <teigland@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/dlm/ast.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/fs/dlm/ast.c
+++ b/fs/dlm/ast.c
@@ -198,13 +198,13 @@ void dlm_add_cb(struct dlm_lkb *lkb, uin
 	if (!prev_seq) {
 		kref_get(&lkb->lkb_ref);
 
+		mutex_lock(&ls->ls_cb_mutex);
 		if (test_bit(LSFL_CB_DELAY, &ls->ls_flags)) {
-			mutex_lock(&ls->ls_cb_mutex);
 			list_add(&lkb->lkb_cb_list, &ls->ls_cb_delay);
-			mutex_unlock(&ls->ls_cb_mutex);
 		} else {
 			queue_work(ls->ls_callback_wq, &lkb->lkb_cb_work);
 		}
+		mutex_unlock(&ls->ls_cb_mutex);
 	}
  out:
 	mutex_unlock(&lkb->lkb_cb_mutex);
@@ -284,7 +284,9 @@ void dlm_callback_stop(struct dlm_ls *ls
 
 void dlm_callback_suspend(struct dlm_ls *ls)
 {
+	mutex_lock(&ls->ls_cb_mutex);
 	set_bit(LSFL_CB_DELAY, &ls->ls_flags);
+	mutex_unlock(&ls->ls_cb_mutex);
 
 	if (ls->ls_callback_wq)
 		flush_workqueue(ls->ls_callback_wq);