Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754729AbZGBOhX (ORCPT ); Thu, 2 Jul 2009 10:37:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752043AbZGBOhM (ORCPT ); Thu, 2 Jul 2009 10:37:12 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:53248 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753127AbZGBOhM (ORCPT ); Thu, 2 Jul 2009 10:37:12 -0400 Date: Thu, 2 Jul 2009 10:37:14 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Andrew Morton cc: Thomas Gleixner , Kernel development list , Oleg Nesterov , Ingo Molnar Subject: Re: Deleting timers In-Reply-To: <20090701222234.ee049bc0.akpm@linux-foundation.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2729 Lines: 70 On Wed, 1 Jul 2009, Andrew Morton wrote: > On Fri, 26 Jun 2009 15:50:54 -0400 (EDT) Alan Stern wrote: > > > Thomas: > > I'm not Thomas, but I play one on TV. > > > The major difference -- in fact, almost the only difference -- between > > del_timer() and try_to_del_timer_sync() is that try_to_del_timer_sync > > returns a special code (-1) if the timer couldn't be deleted because it > > is currently running, whereas del_timer doesn't check this. > > And del_timer() is heaps faster against a not-pending timer. I have a > vague memory that there are some callsites which do this quite a lot. > > And try_to_del_timer_sync() forgot to do timer_stats_timer_clear_start_info(). > > > Furthermore, the "_sync" in the name suggests that > > try_to_del_timer_sync will wait until a running timer has finished, > > which it clearly does not do. > > yup. > > > Despite these facts, the kerneldoc for try_to_del_timer_sync states > > that it must not be called in interrupt context. Why not? Isn't that > > advice simply wrong? > > : commit fd450b7318b75343fd76b3d95416853e34e72c95 > : Author: Oleg Nesterov > : AuthorDate: Thu Jun 23 00:08:59 2005 -0700 > : Commit: Linus Torvalds > : CommitDate: Thu Jun 23 09:45:16 2005 -0700 > : > : [PATCH] timers: introduce try_to_del_timer_sync() > : > : This patch splits del_timer_sync() into 2 functions. The new one, > : try_to_del_timer_sync(), returns -1 when it hits executing timer. > : > : It can be used in interrupt context, or when the caller hold locks which > : can prevent completion of the timer's handler. > : > : NOTE. Currently it can't be used in interrupt context in UP case, because > : ->running_timer is used only with CONFIG_SMP. > : > : Should the need arise, it is possible to kill #ifdef CONFIG_SMP in > : set_running_timer(), it is cheap. > : > > The changelog is somewhat vodka-fogged, but there is a bit of a problem > there. Okay, thanks. That makes sense. > > With this in mind, would there be any objection if I renamed it to > > try_to_del_timer(), removed the comment forbidding it to be used in > > interrupt context, and made it available even on non-SMP builds? > > Sounds sane to me, if the set_running_timer() change is also made. It turns out I probably don't need the enhanced functionality after all. So never mind for now... Alan Stern -- 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/