From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751281AbeDDHhX (ORCPT ); Wed, 4 Apr 2018 03:37:23 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:60796 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750779AbeDDHhW (ORCPT ); Wed, 4 Apr 2018 03:37:22 -0400 Date: Wed, 4 Apr 2018 09:37:15 +0200 From: Sebastian Andrzej Siewior To: Daniel Wagner Cc: linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Steven Rostedt , stable-rt@vger.kernel.org Subject: Re: [PATCH RT 1/3] alarmtimer: Prevent live lock in alarm_cancel() Message-ID: <20180404073715.gwiabamwvvyi2bum@linutronix.de> References: <20180328100746.18668-1-bigeasy@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180323 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018-04-03 20:32:36 [+0200], Daniel Wagner wrote: > Hi Sebastian, > > On 03/28/2018 12:07 PM, Sebastian Andrzej Siewior wrote: > > If alarm_try_to_cancel() requires a retry, then depending on the > > priority setting the retry loop might prevent timer callback completion > > on RT. Prevent that by waiting for completion on RT, no change for a > > non RT kernel. > > > > Cc: stable-rt@vger.kernel.org > > How relevant is this serie for trees before eae1c4ae275f ("posix-timers: > Make use of cancel/arm callbacks")? Patch #2 seems to depend on that change > which was added in v4.12. so #1 looks relevant since that alarmtimer was introduced. #2 since the change you mentioned because after that patch alarmtimer would be handled wrongly - before you should do the schedule_timout() which should be fine. And #3 since 3.0+ (since the RCU-readsection was added) but it is not easy to trigger (you would have to delete the timer while a callback is waiting for it). > Thanks, > Daniel Sebastian