From mboxrd@z Thu Jan 1 00:00:00 1970 From: Maxim Levitsky Subject: Re: [linux-pm] QUESTION: How to fix race between .suspend routine and watchdog timer Date: Sat, 27 Oct 2007 21:19:44 +0200 Message-ID: <200710272119.44574.maximlevitsky@gmail.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-pm@lists.linux-foundation.org To: Alan Stern Return-path: Received: from ug-out-1314.google.com ([66.249.92.171]:19445 "EHLO ug-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751800AbXJ0TWp (ORCPT ); Sat, 27 Oct 2007 15:22:45 -0400 Received: by ug-out-1314.google.com with SMTP id z38so824723ugc for ; Sat, 27 Oct 2007 12:22:43 -0700 (PDT) In-Reply-To: Content-Disposition: inline Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Saturday 27 October 2007 21:17:55 Alan Stern wrote: > On Fri, 26 Oct 2007, Maxim Levitsky wrote: > > > > > Looking through the dmfe code, I noticed yet another possible race. > > > > A race between the .suspend, and a timer that serves both as a watchdog, and link state detector. > > > > Again I need to prevent it from running during the suspend/resume, but how? > > > > > > > > I can use del_timer in .suspend, and mod_timer in .resume, but that doesn't protect against > > > > race with already running timer. > > > > I can use del_timer_sync, but it states that it is useless if timer re-enables itself, and I agree with that. > > > > In dmfe case the timer does re-enable itself. > > > > > > That comment isn't right. del_timer_sync works perfectly well even if > > > the timer routine re-enables itself, provided it stops doing so after a > > > small number of iterations. > > Thanks for the info. but.... > > Due to the "don't access the hardware, while powered-off" rule, I must know that the timer isn't running. > > and won't be. > > So what function to use (if possible) to be sure that the timer won't run anymore? > > (Taking in the account the fact that it re-enables itself) > > Use del_timer_sync(). It guarantees that when it returns, the timer > will be stopped and the timer routine will no longer be running on any > CPU. > Even if the timer re-enables itself, are you sure? > Alan Stern > > Best regards, Maxim Levitsky