From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D730DEE4993 for ; Tue, 22 Aug 2023 19:12:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230056AbjHVTMd (ORCPT ); Tue, 22 Aug 2023 15:12:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39216 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229462AbjHVTMc (ORCPT ); Tue, 22 Aug 2023 15:12:32 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9AB00CE5 for ; Tue, 22 Aug 2023 12:11:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1692731506; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Shv17jTZAkKCjE44GHF0Xqxtw72d64wxEGUZCylGcP4=; b=Jy2SmZdqE46Ai57aGPUhM/koHk8V0RUjevw7DzI6Lhm3341je2ofWHwFX5gJgOLlQSuMiQ 7/163uFPrIRjx4PwNde2bhazqMqEPIPg5K/oNXIOzybWQmyO6H+LIkmaX23MqjuTzDo64b MJkUv/vb/TyTGvqRlOLqx+YaAOng5V4= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-349-6R8jjTdHNSyiUhChpqQXXw-1; Tue, 22 Aug 2023 15:11:42 -0400 X-MC-Unique: 6R8jjTdHNSyiUhChpqQXXw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 906BD85C6E2; Tue, 22 Aug 2023 19:11:41 +0000 (UTC) Received: from [10.22.17.88] (unknown [10.22.17.88]) by smtp.corp.redhat.com (Postfix) with ESMTP id 57BD340C2073; Tue, 22 Aug 2023 19:11:40 +0000 (UTC) Message-ID: <034a302d-773d-5bdb-a32b-bd283d6c7710@redhat.com> Date: Tue, 22 Aug 2023 15:11:40 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH v5 02/19] locking/mutex: Removes wakeups from under mutex::wait_lock Content-Language: en-US To: John Stultz , LKML Cc: Joel Fernandes , Qais Yousef , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Valentin Schneider , Steven Rostedt , Ben Segall , Zimuzo Ezeozue , Youssef Esmat , Mel Gorman , Daniel Bristot de Oliveira , Will Deacon , Boqun Feng , "Paul E . McKenney" , kernel-team@android.com References: <20230819060915.3001568-1-jstultz@google.com> <20230819060915.3001568-3-jstultz@google.com> From: Waiman Long In-Reply-To: <20230819060915.3001568-3-jstultz@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/19/23 02:08, John Stultz wrote: > In preparation to nest mutex::wait_lock under rq::lock we need to remove > wakeups from under it. > > Cc: Joel Fernandes > Cc: Qais Yousef > Cc: Ingo Molnar > Cc: Peter Zijlstra > Cc: Juri Lelli > Cc: Vincent Guittot > Cc: Dietmar Eggemann > Cc: Valentin Schneider > Cc: Steven Rostedt > Cc: Ben Segall > Cc: Zimuzo Ezeozue > Cc: Youssef Esmat > Cc: Mel Gorman > Cc: Daniel Bristot de Oliveira > Cc: Will Deacon > Cc: Waiman Long > Cc: Boqun Feng > Cc: "Paul E . McKenney" > Cc: kernel-team@android.com > Signed-off-by: Peter Zijlstra (Intel) > [Heavily changed after 55f036ca7e74 ("locking: WW mutex cleanup") and > 08295b3b5bee ("locking: Implement an algorithm choice for Wound-Wait > mutexes")] > Signed-off-by: Juri Lelli > [jstultz: rebased to mainline, added extra wake_up_q & init > to avoid hangs, similar to Connor's rework of this patch] > Signed-off-by: John Stultz > --- > v5: > * Reverted back to an earlier version of this patch to undo > the change that kept the wake_q in the ctx structure, as > that broke the rule that the wake_q must always be on the > stack, as its not safe for concurrency. > --- > kernel/locking/mutex.c | 15 ++++++++++++--- > kernel/locking/ww_mutex.h | 29 ++++++++++++++++++----------- > 2 files changed, 30 insertions(+), 14 deletions(-) > > diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c > index d973fe6041bf..118b6412845c 100644 > --- a/kernel/locking/mutex.c > +++ b/kernel/locking/mutex.c > @@ -570,6 +570,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas > struct lockdep_map *nest_lock, unsigned long ip, > struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx) > { > + DEFINE_WAKE_Q(wake_q); > struct mutex_waiter waiter; > struct ww_mutex *ww; > int ret; > @@ -620,7 +621,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas > */ > if (__mutex_trylock(lock)) { > if (ww_ctx) > - __ww_mutex_check_waiters(lock, ww_ctx); > + __ww_mutex_check_waiters(lock, ww_ctx, &wake_q); > > goto skip_wait; > } > @@ -640,7 +641,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas > * Add in stamp order, waking up waiters that must kill > * themselves. > */ > - ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx); > + ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx, &wake_q); > if (ret) > goto err_early_kill; > } > @@ -676,6 +677,10 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas > } > > raw_spin_unlock(&lock->wait_lock); > + /* Make sure we do wakeups before calling schedule */ > + wake_up_q(&wake_q); > + wake_q_init(&wake_q); > + The wake_q may have task to wake up only in the case of ww_mutex which is a minority in the kernel. IOW, wake_up_q() which is a function call will do nothing in most cases. From an optimization point of view, it is better to do a "!wake_q_empty(&wake_q)" check before calling wake_up_q(). > schedule_preempt_disabled(); > > first = __mutex_waiter_is_first(lock, &waiter); > @@ -709,7 +714,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas > */ > if (!ww_ctx->is_wait_die && > !__mutex_waiter_is_first(lock, &waiter)) > - __ww_mutex_check_waiters(lock, ww_ctx); > + __ww_mutex_check_waiters(lock, ww_ctx, &wake_q); > } > > __mutex_remove_waiter(lock, &waiter); > @@ -725,6 +730,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas > ww_mutex_lock_acquired(ww, ww_ctx); > > raw_spin_unlock(&lock->wait_lock); > + wake_up_q(&wake_q); > preempt_enable(); > return 0; > > @@ -736,6 +742,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas > raw_spin_unlock(&lock->wait_lock); > debug_mutex_free_waiter(&waiter); > mutex_release(&lock->dep_map, ip); > + wake_up_q(&wake_q); > preempt_enable(); > return ret; > } > @@ -946,9 +953,11 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne > if (owner & MUTEX_FLAG_HANDOFF) > __mutex_handoff(lock, next); > > + preempt_disable(); > raw_spin_unlock(&lock->wait_lock); > > wake_up_q(&wake_q); > + preempt_enable(); > } I think it looks better to put the preempt_disable() right before raw_spin_lock() for proper nesting. Cheers, Longman