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Commit 1166fde6 authored by Trond Myklebust's avatar Trond Myklebust
Browse files

SUNRPC: Add barriers to ensure read ordering in rpc_wake_up_task_queue_locked 



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: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@vger.kernel.org
parent 24028672

net/sunrpc/sched.c

+7 −2
Original line number Diff line number Diff line
@@ -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]);

	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",
@@ -430,9 +432,12 @@ 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)

	if (RPC_IS_QUEUED(task)) {

		smp_rmb();

		if (task->tk_waitqueue == queue)

			__rpc_do_wake_up_task(queue, task);

	}

}



/*

 * Tests whether rpc queue is empty