From patchwork Tue Jun 4 16:55:21 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kamal Mostafa X-Patchwork-Id: 248774 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from huckleberry.canonical.com (huckleberry.canonical.com [91.189.94.19]) by ozlabs.org (Postfix) with ESMTP id 897CE2C009C for ; Wed, 5 Jun 2013 03:03:20 +1000 (EST) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1Ujudc-0000n4-RQ; Tue, 04 Jun 2013 17:03:12 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1UjudV-0000jR-Qb for kernel-team@lists.ubuntu.com; Tue, 04 Jun 2013 17:03:05 +0000 Received: from c-67-160-231-42.hsd1.ca.comcast.net ([67.160.231.42] helo=fourier) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1UjuXs-0003Dp-9E; Tue, 04 Jun 2013 16:57:16 +0000 Received: from kamal by fourier with local (Exim 4.80) (envelope-from ) id 1UjuXq-0002sq-1u; Tue, 04 Jun 2013 09:57:14 -0700 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Subject: [PATCH 37/75] SUNRPC: Prevent an rpc_task wakeup race Date: Tue, 4 Jun 2013 09:55:21 -0700 Message-Id: <1370364959-9475-38-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1370364959-9475-1-git-send-email-kamal@canonical.com> References: <1370364959-9475-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.8 Cc: Kamal Mostafa , Trond Myklebust X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.14 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: kernel-team-bounces@lists.ubuntu.com 3.8.13.2 -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: Kamal Mostafa --- net/sunrpc/sched.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) 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);