From a3c3cac5d31879cd9ae2de7874dc6544ca704aec Mon Sep 17 00:00:00 2001 From: Trond Myklebust Date: Wed, 22 May 2013 12:57:24 -0400 Subject: 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: Trond Myklebust Cc: stable@vger.kernel.org diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c index f8529fc..5356b12 100644 --- a/net/sunrpc/sched.c +++ b/net/sunrpc/sched.c @@ -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); -- cgit v0.10.2