From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934075AbbI2Jmz (ORCPT ); Tue, 29 Sep 2015 05:42:55 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:60475 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933513AbbI2Jmq (ORCPT ); Tue, 29 Sep 2015 05:42:46 -0400 Message-Id: <20150929093520.037072067@infradead.org> User-Agent: quilt/0.61-1 Date: Tue, 29 Sep 2015 11:28:29 +0200 From: Peter Zijlstra To: mingo@kernel.org Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, fweisbec@gmail.com, oleg@redhat.com, umgwanakikbuti@gmail.com, tglx@linutronix.de, rostedt@goodmis.org, Peter Zijlstra Subject: [RFC][PATCH 04/11] sched: Rework TASK_DEAD preemption exception References: <20150929092825.540553633@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline; filename=peterz-kill-preempt_active-4.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org TASK_DEAD is special in that the final schedule call from do_exit() must be done with preemption disabled. This leads to a violation of our new scheduling invariant which states that the preempt count should be 2. Move the check for TASK_DEAD out of the debug check and use it to decrement the preempt count (from 2 to 1). Signed-off-by: Peter Zijlstra (Intel) --- kernel/sched/core.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2955,12 +2955,8 @@ static inline void schedule_debug(struct #ifdef CONFIG_SCHED_STACK_END_CHECK BUG_ON(unlikely(task_stack_end_corrupted(prev))); #endif - /* - * Test if we are atomic. Since do_exit() needs to call into - * schedule() atomically, we ignore that path. Otherwise whine - * if we are scheduling when we should not. - */ - if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD)) { + + if (unlikely(in_atomic_preempt_off())) { __schedule_bug(prev); preempt_count_set(PREEMPT_DISABLED); } @@ -3061,6 +3057,17 @@ static void __sched __schedule(void) rcu_note_context_switch(); prev = rq->curr; + /* + * do_exit() calls schedule() with preemption disabled as an exception; + * however we must fix that up, otherwise the next task will see an + * inconsistent preempt count. + * + * It also avoids the below schedule_debug() test from complaining + * about this. + */ + if (unlikely(prev->state == TASK_DEAD)) + preempt_enable_no_resched_notrace(); + schedule_debug(prev); if (sched_feat(HRTICK))