Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752057AbbH2Cmg (ORCPT ); Fri, 28 Aug 2015 22:42:36 -0400 Received: from mail-pa0-f41.google.com ([209.85.220.41]:34313 "EHLO mail-pa0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752023AbbH2Cmd (ORCPT ); Fri, 28 Aug 2015 22:42:33 -0400 Message-ID: <1440816150.8932.123.camel@edumazet-glaptop2.roam.corp.google.com> Subject: [PATCH] task_work: remove fifo ordering guarantee From: Eric Dumazet To: Al Viro , Linus Torvalds Cc: "linux-kernel@vger.kernel.org" , Oleg Nesterov , Andrew Morton , Thomas Gleixner , Ingo Molnar , Maciej =?UTF-8?Q?=C5=BBenczykowski?= Date: Fri, 28 Aug 2015 19:42:30 -0700 Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1900 Lines: 60 From: Eric Dumazet In commit f341861fb0b ("task_work: add a scheduling point in task_work_run()") I fixed a latency problem adding a cond_resched() call. Later, commit ac3d0da8f329 added yet another loop to reverse a list, bringing back the latency spike : I've seen in some cases this loop taking 275 ms, if for example a process with 2,000,000 files is killed. We could add yet another cond_resched() in the reverse loop, or we can simply remove the reversal, as I do not think anything would depend on order of task_work_add() submitted works. Fixes: ac3d0da8f329 ("task_work: Make task_work_add() lockless") Signed-off-by: Eric Dumazet Reported-by: Maciej Żenczykowski --- kernel/task_work.c | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-) diff --git a/kernel/task_work.c b/kernel/task_work.c index 8727032e3a6f..53fa971d000d 100644 --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -18,6 +18,8 @@ static struct callback_head work_exited; /* all we need is ->next == NULL */ * This is like the signal handler which runs in kernel mode, but it doesn't * try to wake up the @task. * + * Note: there is no ordering guarantee on works queued here. + * * RETURNS: * 0 if succeeds or -ESRCH. */ @@ -108,16 +110,6 @@ void task_work_run(void) raw_spin_unlock_wait(&task->pi_lock); smp_mb(); - /* Reverse the list to run the works in fifo order */ - head = NULL; - do { - next = work->next; - work->next = head; - head = work; - work = next; - } while (work); - - work = head; do { next = work->next; work->func(work); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/