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SUNRPC: Add barriers to ensure read ordering in rpc_wake_up_task_queue_locked

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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>
Cc: stable@vger.kernel.org
This commit is contained in:
Trond Myklebust
2013-03-25 11:23:40 -04:00
parent 240286725d
commit 1166fde6a9
1 changed files with 7 additions and 2 deletions
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9
net/sunrpc/sched.c
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@@ -180,6 +180,8 @@ static void __rpc_add_wait_queue(struct rpc_wait_queue *queue,
list_add_tail(&task->u.tk_wait.list, &queue->tasks[0]); list_add_tail(&task->u.tk_wait.list, &queue->tasks[0]);
task->tk_waitqueue = queue; task->tk_waitqueue = queue;
queue->qlen++; queue->qlen++;
/* barrier matches the read in rpc_wake_up_task_queue_locked() */
smp_wmb();
rpc_set_queued(task); rpc_set_queued(task);
dprintk("RPC: %5u added to queue %p \"%s\"\n", dprintk("RPC: %5u added to queue %p \"%s\"\n",
@@ -430,8 +432,11 @@ 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) 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) if (RPC_IS_QUEUED(task)) {
__rpc_do_wake_up_task(queue, task); smp_rmb();
if (task->tk_waitqueue == queue)
__rpc_do_wake_up_task(queue, task);
}
} }
/* /*