From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Trond Myklebust , Ben Hutchings , Weng Meiling Subject: [PATCH 3.4 78/99] SUNRPC: Prevent an rpc_task wakeup race Date: Fri, 7 Mar 2014 17:08:14 -0800 Message-Id: <20140308010614.094996541@linuxfoundation.org> In-Reply-To: <20140308010611.468206150@linuxfoundation.org> References: <20140308010611.468206150@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Trond Myklebust commit a3c3cac5d31879cd9ae2de7874dc6544ca704aec upstream. 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 Signed-off-by: Ben Hutchings Cc: Weng Meiling Signed-off-by: Greg Kroah-Hartman --- net/sunrpc/sched.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) --- a/net/sunrpc/sched.c +++ b/net/sunrpc/sched.c @@ -305,11 +305,17 @@ EXPORT_SYMBOL_GPL(__rpc_wait_for_complet * 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);