Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751922AbdI2IAI (ORCPT ); Fri, 29 Sep 2017 04:00:08 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:59892 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751037AbdI2IAH (ORCPT ); Fri, 29 Sep 2017 04:00:07 -0400 Date: Fri, 29 Sep 2017 09:59:55 +0200 (CEST) From: Thomas Gleixner To: Junaid Shahid cc: Peter Zijlstra , linux-kernel@vger.kernel.org, Andres Lagar-Cavilla , Greg Thelen , Rusty Russell Subject: Re: [PATCH] kthread: Fix race condition between kthread_parkme() and kthread_unpark() In-Reply-To: Message-ID: References: <20170429023236.60452-1-junaids@google.com> <20170927121706.g5qydxv3v2usmdd5@hirez.programming.kicks-ass.net> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) 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 Content-Length: 655 Lines: 18 On Thu, 28 Sep 2017, Junaid Shahid wrote: > Hi Peter, > > It looks like try_cmpxchg is not available on non-x86 archs, but other than > that the version that you proposed looks good. > > One thing that I am a bit curious about is that the original code, before > either patch, had a test_and_set_bit for KTHREAD_IS_PARKED rather than just > a set_bit. I can't think of any reason why that was needed, since it > doesn't look like TASK_PARKED tasks are susceptible to spurious wakeups. Do > you by any chance happen to know if there was any specific reason for it? Everything is susceptible to spurious wakeups and has to deal with it. Thanks, tglx