From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CBE281DFE04 for ; Fri, 13 Dec 2024 12:46:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734093984; cv=none; b=WtQKBNuET4sfg3ovAoV54PCJlsWdvb9sX5JQ/pJisU9iy/ifE1MpQwqIV/PhsQKUpSJIiaoBxinmMZv4424wWzJOx8Hc1+9q1yzuwC6K7SEKI8ovtxVhq9OIBp3NwyEaUmUuX+EBhK3SI/Rv1n8IAJxypiM06I68Yh0exEyPIQs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734093984; c=relaxed/simple; bh=thlok1CfL06wcvQX+28Qnz6C04TjoNd5+5nx+qUM5xs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ZNs6mALxTVBUt8xKMNLipGJeeClsGPD6LQUT2wgMsgWBkJzHaQuJm7XRsBd3GL6lJlvrFHFFR2PDmM/noGmNdIe1qLSx/Kx4FeeCO+nU7Qavgh2fn/SbVF59a9DnyiomfXCwekMfzWGDVHCedvSr19Vrcl/45Y8wSLsNSfkdgSQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=B+ft+Ry+; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="B+ft+Ry+" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=kKnnXGxBgrXo8pBr3PlNv3tQuU4P1ia/Phvtxts7lNQ=; b=B+ft+Ry+cYpNY6UkYRhn/+nAiL MOxUohUCE2Cvg2qxxUq+wpGGPyZV8xjfxsV953cAjrPBuooBa3sc3CbvW8MjqBA2wJAGfJ7WXBsl3 kQD5qFLZO0vjXEq0qZ0kHegCO+BPn3sk7oMpCkdiDnj6dAB0IZC8/CpeBCLYAsStzwvGl1Dc9Qv5E jQT5zE7KVPDCgH9gwpwr0zD6u5pwGC9H0UqNXb9vb4jqGGMa8iRn6t3LCXzSdS/cXfqXz32BJP5CR AAin50pK/uMyi9jHUI6megLvLdnzPOFDCWpiLHwYgTChbYg+8/Ruk8DFOVcpFvz1+2btLg4tVr9+I Bvtpu9XA==; Received: from 77-249-17-89.cable.dynamic.v4.ziggo.nl ([77.249.17.89] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tM53f-0000000Cwi0-2sdD; Fri, 13 Dec 2024 12:46:15 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 125CE30049D; Fri, 13 Dec 2024 13:46:15 +0100 (CET) Date: Fri, 13 Dec 2024 13:46:14 +0100 From: Peter Zijlstra To: John Stultz Cc: LKML , Ingo Molnar , Will Deacon , Waiman Long , Boqun Feng , Thomas Gleixner , Bert Karwatzki , kernel-team@android.com Subject: Re: [RFC][PATCH] locking/rtmutex: Make sure we wake anything on the wake_q when we release the lock->wait_lock Message-ID: <20241213124614.GA12338@noisy.programming.kicks-ass.net> References: <20241212222138.2400498-1-jstultz@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241212222138.2400498-1-jstultz@google.com> On Thu, Dec 12, 2024 at 02:21:33PM -0800, John Stultz wrote: > Bert reported seeing occasional boot hangs when running with > PREEPT_RT and bisected it down to commit 894d1b3db41c > ("locking/mutex: Remove wakeups from under mutex::wait_lock"). > > It looks like I missed a few spots where we drop the wait_lock and > potentially call into schedule without waking up the tasks on the > wake_q structure. Since the tasks being woken are ww_mutex tasks > they need to be able to run to release the mutex and unblock the > task that currently is planning to wake them. Thus we can deadlock. > > So make sure we wake the wake_q tasks when we unlock the wait_lock. > > Cc: Peter Zijlstra > Cc: Ingo Molnar > Cc: Will Deacon > Cc: Waiman Long > Cc: Boqun Feng > Cc: Thomas Gleixner > Cc: Bert Karwatzki > Cc: kernel-team@android.com > Reported-by: Bert Karwatzki > Closes: https://lore.kernel.org/lkml/20241211182502.2915-1-spasswolf@web.de > Fixes: 894d1b3db41c ("locking/mutex: Remove wakeups from under mutex::wait_lock") > Signed-off-by: John Stultz > --- I don't suppose this actually makes things much better -- but I had to try. --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1192,6 +1192,17 @@ try_to_take_rt_mutex(struct rt_mutex_bas return 1; } +#define WRAP_WAKE(_stmt, _q) \ +do { \ + struct wake_q_head *_Q = (_q); \ + guard(preempt)(); \ + _stmt; \ + if (_Q && !wake_q_empty(_Q)) { \ + wake_up_q(_Q); \ + wake_q_init(_Q); \ + } \ +} while (0) + /* * Task blocks on lock. * @@ -1248,10 +1259,7 @@ static int __sched task_blocks_on_rt_mut /* Check whether the waiter should back out immediately */ rtm = container_of(lock, struct rt_mutex, rtmutex); - preempt_disable(); - res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx, wake_q); - wake_up_q(wake_q); - preempt_enable(); + WRAP_WAKE(res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx, wake_q), wake_q); if (res) { raw_spin_lock(&task->pi_lock); rt_mutex_dequeue(lock, waiter); @@ -1295,13 +1303,7 @@ static int __sched task_blocks_on_rt_mut */ get_task_struct(owner); - preempt_disable(); - raw_spin_unlock_irq(&lock->wait_lock); - /* wake up any tasks on the wake_q before calling rt_mutex_adjust_prio_chain */ - wake_up_q(wake_q); - wake_q_init(wake_q); - preempt_enable(); - + WRAP_WAKE(raw_spin_unlock_irq(&lock->wait_lock), wake_q); res = rt_mutex_adjust_prio_chain(owner, chwalk, lock, next_lock, waiter, task); @@ -1645,13 +1647,8 @@ static int __sched rt_mutex_slowlock_blo owner = rt_mutex_owner(lock); else owner = NULL; - preempt_disable(); - raw_spin_unlock_irq(&lock->wait_lock); - if (wake_q) { - wake_up_q(wake_q); - wake_q_init(wake_q); - } - preempt_enable(); + + WRAP_WAKE(raw_spin_unlock_irq(&lock->wait_lock), wake_q); if (!owner || !rtmutex_spin_on_owner(lock, waiter, owner)) rt_mutex_schedule(); @@ -1802,10 +1799,7 @@ static int __sched rt_mutex_slowlock(str */ raw_spin_lock_irqsave(&lock->wait_lock, flags); ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state, &wake_q); - preempt_disable(); - raw_spin_unlock_irqrestore(&lock->wait_lock, flags); - wake_up_q(&wake_q); - preempt_enable(); + WRAP_WAKE(raw_spin_unlock_irqrestore(&lock->wait_lock, flags), &wake_q); rt_mutex_post_schedule(); return ret; @@ -1863,11 +1857,8 @@ static void __sched rtlock_slowlock_lock owner = rt_mutex_owner(lock); else owner = NULL; - preempt_disable(); - raw_spin_unlock_irq(&lock->wait_lock); - wake_up_q(wake_q); - wake_q_init(wake_q); - preempt_enable(); + + WRAP_WAKE(raw_spin_unlock_irq(&lock->wait_lock), wake_q); if (!owner || !rtmutex_spin_on_owner(lock, &waiter, owner)) schedule_rtlock(); @@ -1896,10 +1887,8 @@ static __always_inline void __sched rtlo raw_spin_lock_irqsave(&lock->wait_lock, flags); rtlock_slowlock_locked(lock, &wake_q); - preempt_disable(); - raw_spin_unlock_irqrestore(&lock->wait_lock, flags); - wake_up_q(&wake_q); - preempt_enable(); + + WRAP_WAKE(raw_spin_unlock_irqrestore(&lock->wait_lock, flags), &wake_q); } #endif /* RT_MUTEX_BUILD_SPINLOCKS */