[PATCH] SUNRPC: Fix potential deadlock in RPC code

In rpc_wake_up() and rpc_wake_up_status(), it is possible for the call to
__rpc_wake_up_task() to fail if another thread happens to be calling
rpc_wake_up_task() on the same rpc_task.

Problem noticed by Bruno Faccini.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 8 deletions

diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index 802d4fe0f55c..e838d042f7f5 100644
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -515,16 +515,14 @@ struct rpc_task * rpc_wake_up_next(struct rpc_wait_queue *queue)
  */
 void rpc_wake_up(struct rpc_wait_queue *queue)
 {
-        struct rpc_task *task;
-
+        struct rpc_task *task, *next;
         struct list_head *head;
+
         spin_lock_bh(&queue->lock);
         head = &queue->tasks[queue->maxpriority];
         for (;;) {
-                while (!list_empty(head)) {
-                        task = list_entry(head->next, struct rpc_task, u.tk_wait.list);
+                list_for_each_entry_safe(task, next, head, u.tk_wait.list)
                         __rpc_wake_up_task(task);
-                }
                 if (head == &queue->tasks[0])
                         break;
                 head--;
@@ -541,14 +539,13 @@ void rpc_wake_up(struct rpc_wait_queue *queue)
  */
 void rpc_wake_up_status(struct rpc_wait_queue *queue, int status)
 {
+        struct rpc_task *task, *next;
         struct list_head *head;
-        struct rpc_task *task;
 
         spin_lock_bh(&queue->lock);
         head = &queue->tasks[queue->maxpriority];
         for (;;) {
-                while (!list_empty(head)) {
-                        task = list_entry(head->next, struct rpc_task, u.tk_wait.list);
+                list_for_each_entry_safe(task, next, head, u.tk_wait.list) {
                         task->tk_status = status;
                         __rpc_wake_up_task(task);
                 }