From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758652AbcIHQsV (ORCPT ); Thu, 8 Sep 2016 12:48:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48936 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754147AbcIHQsT (ORCPT ); Thu, 8 Sep 2016 12:48:19 -0400 Date: Thu, 8 Sep 2016 18:48:15 +0200 From: Oleg Nesterov To: Ingo Molnar , Peter Zijlstra Cc: Al Viro , Bart Van Assche , Johannes Weiner , Linus Torvalds , Neil Brown , linux-kernel@vger.kernel.org Subject: [PATCH V3 2/4] sched/wait: avoid abort_exclusive_wait() in ___wait_event() Message-ID: <20160908164815.GA18801@redhat.com> References: <20160906140013.GA6139@redhat.com> <20160906140050.GA6160@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160906140050.GA6160@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Thu, 08 Sep 2016 16:48:19 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/06, Oleg Nesterov wrote: > > + if (unlikely(signal_pending_state(state, current))) { > + /* > + * Exclusive waiter must not fail if it was selected by wakeup, > + * it should "consume" the condition we were waiting for. > + * > + * The caller will recheck the condition and return success if > + * we were already woken up, we can not miss the event because > + * wakeup locks/unlocks the same q->lock. > + * > + * But we need to ensure that set-condition + wakeup after that > + * can't see us, it should wake up another exclusive waiter if > + * we fail. > + */ > + list_del_init(&wait->task_list); > + ret = -ERESTARTSYS; Yes, but we should not do set_current_state() in this case, please sere V3. ------------------------------------------------------------------------------- Subject: [PATCH V3 2/4] sched/wait: avoid abort_exclusive_wait() in ___wait_event() ___wait_event() doesn't really need abort_exclusive_wait(), we can simply change prepare_to_wait_event() to remove the waiter from q->task_list if it was interrupted. This simplifies the code/logic, and this way prepare_to_wait_event() can have more users, see the next change. Signed-off-by: Oleg Nesterov --- include/linux/wait.h | 7 +------ kernel/sched/wait.c | 35 +++++++++++++++++++++++++---------- 2 files changed, 26 insertions(+), 16 deletions(-) diff --git a/include/linux/wait.h b/include/linux/wait.h index 329f796..5179915 100644 --- a/include/linux/wait.h +++ b/include/linux/wait.h @@ -280,12 +280,7 @@ wait_queue_head_t *bit_waitqueue(void *, int); \ if (___wait_is_interruptible(state) && __int) { \ __ret = __int; \ - if (exclusive) { \ - abort_exclusive_wait(&wq, &__wait, \ - NULL); \ - goto __out; \ - } \ - break; \ + goto __out; \ } \ \ cmd; \ diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c index 2bbba01..2612393 100644 --- a/kernel/sched/wait.c +++ b/kernel/sched/wait.c @@ -199,24 +199,39 @@ EXPORT_SYMBOL(prepare_to_wait_exclusive); long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state) { unsigned long flags; - - if (signal_pending_state(state, current)) - return -ERESTARTSYS; + long ret = 0; wait->private = current; wait->func = autoremove_wake_function; spin_lock_irqsave(&q->lock, flags); - if (list_empty(&wait->task_list)) { - if (wait->flags & WQ_FLAG_EXCLUSIVE) - __add_wait_queue_tail(q, wait); - else - __add_wait_queue(q, wait); + if (unlikely(signal_pending_state(state, current))) { + /* + * Exclusive waiter must not fail if it was selected by wakeup, + * it should "consume" the condition we were waiting for. + * + * The caller will recheck the condition and return success if + * we were already woken up, we can not miss the event because + * wakeup locks/unlocks the same q->lock. + * + * But we need to ensure that set-condition + wakeup after that + * can't see us, it should wake up another exclusive waiter if + * we fail. + */ + list_del_init(&wait->task_list); + ret = -ERESTARTSYS; + } else { + if (list_empty(&wait->task_list)) { + if (wait->flags & WQ_FLAG_EXCLUSIVE) + __add_wait_queue_tail(q, wait); + else + __add_wait_queue(q, wait); + } + set_current_state(state); } - set_current_state(state); spin_unlock_irqrestore(&q->lock, flags); - return 0; + return ret; } EXPORT_SYMBOL(prepare_to_wait_event); -- 2.5.0