From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757167AbaGNVnC (ORCPT ); Mon, 14 Jul 2014 17:43:02 -0400 Received: from www.linutronix.de ([62.245.132.108]:42563 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756358AbaGNVm7 (ORCPT ); Mon, 14 Jul 2014 17:42:59 -0400 Date: Mon, 14 Jul 2014 23:42:53 +0200 (CEST) From: Thomas Gleixner To: Lai Jiangshan cc: Tejun Heo , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1 V2] workqueue: remove the del_timer_sync()s in maybe_create_worker() In-Reply-To: <53C44915.4000405@cn.fujitsu.com> Message-ID: References: <1405265479-827-1-git-send-email-laijs@cn.fujitsu.com> <1405325601-12437-1-git-send-email-laijs@cn.fujitsu.com> <1405325601-12437-2-git-send-email-laijs@cn.fujitsu.com> <20140714142707.GB31610@htj.dyndns.org> <53C44915.4000405@cn.fujitsu.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 15 Jul 2014, Lai Jiangshan wrote: > On 07/14/2014 11:33 PM, Thomas Gleixner wrote: > > On Mon, 14 Jul 2014, Tejun Heo wrote: > > > >> Hello, > >> > >> On Mon, Jul 14, 2014 at 04:13:21PM +0800, Lai Jiangshan wrote: > >>> It is said in the document that the timer which is being > >>> deleted by del_timer_sync() should not be restarted: > >>> Synchronization rules: Callers must prevent restarting of > >>> the timer, otherwise this function is meaningless. > >>> > >>> Repeating timer may cause the del_timer_sync() spin longer, > >>> or even spin forever in very very very very extreme condition. > >> > >> I'm fairly sure del_timer_sync() can delete self-requeueing timers. > >> The implementation busy-waits if the queued timer is the currently > >> executing one and dequeues only while the timer isn't running which > >> should be able to handle self-requeueing ones just fine. Thomas, > >> del_timer_sync() can reliably delete self-requeueing ones, right? > > > > Yes. > > The comments of the del_timer_sync() needs to be updated > if I did not misunderstood? > > > If the timer callback is running on the other cpu, then it waits > > for the callback to finish before checking whether the timer is > > enqueued or not. > > The syncer may be interrupted here, after it comes back, the timer > may be running again (and maybe again and again). No. The del_timer_sync() code holds the base lock with interrupts disabled. So it can't be interrupted. Thanks, tglx