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 X-Spam-Level: X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8DD78C433F5 for ; Tue, 14 Sep 2021 10:42:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7206C6113E for ; Tue, 14 Sep 2021 10:42:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231873AbhINKoB (ORCPT ); Tue, 14 Sep 2021 06:44:01 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:60948 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231401AbhINKoA (ORCPT ); Tue, 14 Sep 2021 06:44:00 -0400 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1631616162; 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: in-reply-to:in-reply-to:references:references; bh=lOP4d2X9VL4G2q0tjsxLQr1jdG3jIE3tqu86UTFeOZU=; b=iAvWzrHYkdE1Z0l3+uQBj/Gt5AADtXrQq95Jq5djCmJbqXQY1XnMcT6bAl8xSyrx9wcI0j CKH3WwbzxqNz5c5OYE78G2Fvhe+Y/T7Oe/rQ4Bm4slk+4Z9AnBizgkKWoqAP20peWGsLti AjxBULd0TTiCFszytSglLr1WiEH7yKt2oL9iovQFP6xjBnU/hfPr/UASbGf0Uzo7vP1eKF R7JJjmWCoXHEy14PFVsHg9B+lfWnNTPo3sCxfcXStG+QghXoghm0OwYvXLRB9fzMicOmYt 2m3bPYAl6PGKCLAGgNOyPBE40xORHMO5pTLW6PaWWVxERGdwqjg23/UuDElslA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1631616162; 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: in-reply-to:in-reply-to:references:references; bh=lOP4d2X9VL4G2q0tjsxLQr1jdG3jIE3tqu86UTFeOZU=; b=6Ketdid8ptA3EDshSAE8DXVsMVdA65dml7RT3ptpmqV92heONmms+btnwhDmBT1m1a5GUC FZHq7fwwNlkvqyBg== To: Davidlohr Bueso Cc: peterz@infradead.org, mingo@kernel.org, rostedt@goodmis.org, longman@redhat.com, bigeasy@linutronix.de, boqun.feng@gmail.com, dave@stgolabs.net, linux-kernel@vger.kernel.org, Davidlohr Bueso Subject: Re: [PATCH 2/2] locking/rwbase_rt: Lockless reader waking up a writer In-Reply-To: <87ilz4fyzi.ffs@tglx> References: <20210901222825.6313-1-dave@stgolabs.net> <20210901222825.6313-3-dave@stgolabs.net> <87ilz4fyzi.ffs@tglx> Date: Tue, 14 Sep 2021 12:42:41 +0200 Message-ID: <87wnnjcuam.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 13 2021 at 14:20, Thomas Gleixner wrote: > On Wed, Sep 01 2021 at 15:28, Davidlohr Bueso wrote: >> diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c >> index 4ba15088e640..3444bc709973 100644 >> --- a/kernel/locking/rwbase_rt.c >> +++ b/kernel/locking/rwbase_rt.c >> @@ -141,6 +141,7 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt *rwb, >> { >> struct rt_mutex_base *rtm = &rwb->rtmutex; >> struct task_struct *owner; >> + DEFINE_WAKE_Q(wake_q); >> >> raw_spin_lock_irq(&rtm->wait_lock); >> /* >> @@ -151,9 +152,10 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt *rwb, >> */ >> owner = rt_mutex_owner(rtm); >> if (owner) >> - wake_up_state(owner, state); >> + wake_q_add(&wake_q, owner); > > That's broken for rw_locks. See commit 456cfbc65cd072f4f53936ee5a37eb1447a7d3ba. Something like the untested below should work. Thanks, tglx --- diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 6bb116c559b4..9e04bca0c11e 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -459,6 +459,20 @@ static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh, } } +static __always_inline void rt_mutex_wake_q_add_task(struct rt_wake_q_head *wqh, + struct task_struct *task, + unsigned int wake_state) +{ + if (IS_ENABLED(CONFIG_PREEMPT_RT) && wake_state != TASK_NORMAL) { + if (IS_ENABLED(CONFIG_PROVE_LOCKING)) + WARN_ON_ONCE(wqh->rtlock_task); + get_task_struct(task); + wqh->rtlock_task = task; + } else { + wake_q_add(&wqh->head, task); + } +} + static __always_inline void rt_mutex_wake_up_q(struct rt_wake_q_head *wqh) { if (IS_ENABLED(CONFIG_PREEMPT_RT) && wqh->rtlock_task) { diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c index 4ba15088e640..e011b347a2c5 100644 --- a/kernel/locking/rwbase_rt.c +++ b/kernel/locking/rwbase_rt.c @@ -141,8 +141,10 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt *rwb, { struct rt_mutex_base *rtm = &rwb->rtmutex; struct task_struct *owner; + DEFINE_RT_WAKE_Q(wqh); raw_spin_lock_irq(&rtm->wait_lock); + /* * Wake the writer, i.e. the rtmutex owner. It might release the * rtmutex concurrently in the fast path (due to a signal), but to @@ -151,9 +153,12 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt *rwb, */ owner = rt_mutex_owner(rtm); if (owner) - wake_up_state(owner, state); + rt_mutex_wake_q_add_task(&wqh, owner, state); + /* Pairs with the preempt_enable in rt_mutex_wake_up_q() */ + preempt_disable(); raw_spin_unlock_irq(&rtm->wait_lock); + rt_mutex_wake_up_q(&wqh); } static __always_inline void rwbase_read_unlock(struct rwbase_rt *rwb,