SUNRPC: Prevent an rpc_task wakeup race (a3c3cac5) · Commits · 戴 / test

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:

Trond Myklebust <Trond.Myklebust@netapp.com> Cc: stable@vger.kernel.org

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);

Admin message