From patchwork Mon Sep 28 17:32:20 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Luis Henriques X-Patchwork-Id: 523521 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 E422014017E; Tue, 29 Sep 2015 03:34:09 +1000 (AEST) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1ZgcJS-0002zF-1X; Mon, 28 Sep 2015 17:34:06 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1ZgcHl-0002Bk-MF for kernel-team@lists.ubuntu.com; Mon, 28 Sep 2015 17:32:21 +0000 Received: from 1.general.henrix.uk.vpn ([10.172.192.212] helo=localhost) by youngberry.canonical.com with esmtpsa (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.76) (envelope-from ) id 1ZgcHl-00025s-H7; Mon, 28 Sep 2015 17:32:21 +0000 From: Luis Henriques To: Eric Dumazet Subject: [3.16.y-ckt stable] Patch "task_work: remove fifo ordering guarantee" has been added to staging queue Date: Mon, 28 Sep 2015 18:32:20 +0100 Message-Id: <1443461540-6163-1-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 2.1.4 X-Extended-Stable: 3.16 MIME-Version: 1.0 Cc: =?UTF-8?q?Maciej=20=C5=BBenczykowski?= , kernel-team@lists.ubuntu.com, Linus Torvalds , Al Viro 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: , Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: kernel-team-bounces@lists.ubuntu.com This is a note to let you know that I have just added a patch titled task_work: remove fifo ordering guarantee to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue This patch is scheduled to be released in version 3.16.7-ckt18. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.16.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From 0f37918986de3b0e77e40a743cac2ded1e7cfaad Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 28 Aug 2015 19:42:30 -0700 Subject: task_work: remove fifo ordering guarantee MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit commit c82199061009d1561e31e17fca5e47a87cb7ff4c upstream. 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 Acked-by: Al Viro Signed-off-by: Linus Torvalds Signed-off-by: Luis Henriques --- 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);