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Commit a3c3cac5 authored by Trond Myklebust's avatar Trond Myklebust
Browse files

SUNRPC: Prevent an rpc_task wakeup race 



The lockless RPC_IS_QUEUED() test in __rpc_execute means that we need to
be careful about ordering the calls to rpc_test_and_set_running(task) and
rpc_clear_queued(task). If we get the order wrong, then we may end up
testing the RPC_TASK_RUNNING flag after __rpc_execute() has looped
and changed the state of the rpc_task.

Signed-off-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@vger.kernel.org
parent 774d5f14

net/sunrpc/sched.c

+7 −1
Original line number Diff line number Diff line
@@ -324,11 +324,17 @@ EXPORT_SYMBOL_GPL(__rpc_wait_for_completion_task); 
 * Note: If the task is ASYNC, and is being made runnable after sitting on an

 * rpc_wait_queue, this must be called with the queue spinlock held to protect

 * the wait queue operation.

 * Note the ordering of rpc_test_and_set_running() and rpc_clear_queued(),

 * which is needed to ensure that __rpc_execute() doesn't loop (due to the

 * lockless RPC_IS_QUEUED() test) before we've had a chance to test

 * the RPC_TASK_RUNNING flag.

 */

static void rpc_make_runnable(struct rpc_task *task)

{

	bool need_wakeup = !rpc_test_and_set_running(task);



	rpc_clear_queued(task);

	if (rpc_test_and_set_running(task))

	if (!need_wakeup)

		return;

	if (RPC_IS_ASYNC(task)) {

		INIT_WORK(&task->u.tk_work, rpc_async_schedule);