Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751824AbbBLUBW (ORCPT ); Thu, 12 Feb 2015 15:01:22 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48871 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751573AbbBLUBU (ORCPT ); Thu, 12 Feb 2015 15:01:20 -0500 Date: Thu, 12 Feb 2015 20:59:13 +0100 From: Oleg Nesterov To: "Paul E. McKenney" , Peter Zijlstra Cc: linux-kernel@vger.kernel.org, dave@stgolabs.net, waiman.long@hp.com, raghavendra.kt@linux.vnet.ibm.com Subject: [PATCH] sched/completion: completion_done() should serialize with complete() Message-ID: <20150212195913.GA30430@redhat.com> References: <20150212003430.GA28656@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150212003430.GA28656@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1428 Lines: 46 Commit de30ec47302c "Remove unnecessary ->wait.lock serialization when reading completion state" was not correct, without lock/unlock the code like stop_machine_from_inactive_cpu() while (!completion_done()) cpu_relax(); can return before complete() finishes its spin_unlock() which writes to this memory. And spin_unlock_wait(). While at it, change try_wait_for_completion() to use READ_ONCE(). Reported-by: "Paul E. McKenney" Reported-by: Davidlohr Bueso Signed-off-by: Oleg Nesterov --- x/kernel/sched/completion.c +++ x/kernel/sched/completion.c @@ -274,7 +274,7 @@ bool try_wait_for_completion(struct comp * first without taking the lock so we can * return early in the blocking case. */ - if (!ACCESS_ONCE(x->done)) + if (!READ_ONCE(x->done)) return 0; spin_lock_irqsave(&x->wait.lock, flags); @@ -297,6 +297,11 @@ EXPORT_SYMBOL(try_wait_for_completion); */ bool completion_done(struct completion *x) { - return !!ACCESS_ONCE(x->done); + if (!READ_ONCE(x->done)) + return false; + + smp_rmb(); + spin_unlock_wait(&x->wait.lock); + return true; } EXPORT_SYMBOL(completion_done); -- 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/