Return-Path: linux-nfs-owner@vger.kernel.org Received: from mx2.netapp.com ([216.240.18.37]:62166 "EHLO mx2.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753631Ab3ADSPK (ORCPT ); Fri, 4 Jan 2013 13:15:10 -0500 From: Trond Myklebust To: linux-nfs@vger.kernel.org Cc: Weston Andros Adamson , Tejun Heo , Bruce Fields Subject: [PATCH 1/3] SUNRPC: Ensure that we free the rpc_task after cleanups are done Date: Fri, 4 Jan 2013 13:15:00 -0500 Message-Id: <1357323302-12944-1-git-send-email-Trond.Myklebust@netapp.com> In-Reply-To: <0EC8763B847DB24D9ADF5EBD9CD7B419125A16A9@SACEXCMBX02-PRD.hq.netapp.com> References: <0EC8763B847DB24D9ADF5EBD9CD7B419125A16A9@SACEXCMBX02-PRD.hq.netapp.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: This patch ensures that we free the rpc_task after the cleanup callbacks are done in order to avoid a deadlock problem that can be triggered if the callback needs to wait for another workqueue item to complete. Signed-off-by: Trond Myklebust Cc: Weston Andros Adamson Cc: Tejun Heo Cc: Bruce Fields Cc: stable@vger.kernel.org --- net/sunrpc/sched.c | 27 +++++++++++++++++++++++---- 1 file changed, 23 insertions(+), 4 deletions(-) diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c index d17a704..b4133bd 100644 --- a/net/sunrpc/sched.c +++ b/net/sunrpc/sched.c @@ -934,16 +934,35 @@ struct rpc_task *rpc_new_task(const struct rpc_task_setup *setup_data) return task; } +/* + * rpc_free_task - release rpc task and perform cleanups + * + * Note that we free up the rpc_task _after_ rpc_release_calldata() + * in order to work around a workqueue dependency issue. + * + * Tejun Heo states: + * "Workqueue currently considers two work items to be the same if they're + * on the same address and won't execute them concurrently - ie. it + * makes a work item which is queued again while being executed wait + * for the previous execution to complete. + * + * If a work function frees the work item, and then waits for an event + * which should be performed by another work item and *that* work item + * recycles the freed work item, it can create a false dependency loop. + * There really is no reliable way to detect this short of verifying + * every memory free." + * + */ static void rpc_free_task(struct rpc_task *task) { - const struct rpc_call_ops *tk_ops = task->tk_ops; - void *calldata = task->tk_calldata; + unsigned short tk_flags = task->tk_flags; + + rpc_release_calldata(task->tk_ops, task->tk_calldata); - if (task->tk_flags & RPC_TASK_DYNAMIC) { + if (tk_flags & RPC_TASK_DYNAMIC) { dprintk("RPC: %5u freeing task\n", task->tk_pid); mempool_free(task, rpc_task_mempool); } - rpc_release_calldata(tk_ops, calldata); } static void rpc_async_release(struct work_struct *work) -- 1.7.11.7