From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from youngberry.canonical.com ([91.189.89.112]:43257 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753448AbbJTVgp (ORCPT ); Tue, 20 Oct 2015 17:36:45 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Eric Dumazet , Linus Torvalds , Kamal Mostafa Subject: [PATCH 3.13.y-ckt 84/85] task_work: remove fifo ordering guarantee Date: Tue, 20 Oct 2015 14:35:40 -0700 Message-Id: <1445376941-7046-85-git-send-email-kamal@canonical.com> In-Reply-To: <1445376941-7046-1-git-send-email-kamal@canonical.com> References: <1445376941-7046-1-git-send-email-kamal@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: 3.13.11-ckt28 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet 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: Kamal Mostafa --- 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 8727032..53fa971 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); -- 1.9.1