| From | Luis Henriques <> | Subject | [PATCH 012/102] SUNRPC: Add barriers to ensure read ordering in rpc_wake_up_task_queue_locked | Date | Mon, 8 Apr 2013 10:49:27 +0100 |
| |
3.5.7.10 -stable review patch. If anyone has any objections, please let me know.
------------------
From: Trond Myklebust <Trond.Myklebust@netapp.com>
commit 1166fde6a923c30f4351515b6a9a1efc513e7d00 upstream.
We need to be careful when testing task->tk_waitqueue in rpc_wake_up_task_queue_locked, because it can be changed while we are holding the queue->lock. By adding appropriate memory barriers, we can ensure that it is safe to test task->tk_waitqueue for equality if the RPC_TASK_QUEUED bit is set.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- net/sunrpc/sched.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c index 85b9235..72d89e1 100644 --- a/net/sunrpc/sched.c +++ b/net/sunrpc/sched.c @@ -143,6 +143,8 @@ static void __rpc_add_wait_queue(struct rpc_wait_queue *queue, list_add_tail(&task->u.tk_wait.list, &queue->tasks[0]); task->tk_waitqueue = queue; queue->qlen++; + /* barrier matches the read in rpc_wake_up_task_queue_locked() */ + smp_wmb(); rpc_set_queued(task); dprintk("RPC: %5u added to queue %p \"%s\"\n", @@ -399,8 +401,11 @@ static void __rpc_do_wake_up_task(struct rpc_wait_queue *queue, struct rpc_task */ static void rpc_wake_up_task_queue_locked(struct rpc_wait_queue *queue, struct rpc_task *task) { - if (RPC_IS_QUEUED(task) && task->tk_waitqueue == queue) - __rpc_do_wake_up_task(queue, task); + if (RPC_IS_QUEUED(task)) { + smp_rmb(); + if (task->tk_waitqueue == queue) + __rpc_do_wake_up_task(queue, task); + } } /* -- 1.8.1.2
|