From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4A1A0223337; Thu, 11 Sep 2025 12:20:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757593239; cv=none; b=E14uVAU6b0QZfqWaSWLm0UXJ6NUvEurD2NOoFg8lyDLkCGIuX5rrPGOtqHNj/M/ICgoQCA15SahSNyepoJajfw76JgU7af2tSFcfwyO99+brfd0euT7RbUCrMzpA3LgIEkaPDoH1V72BVBYSykJNqsCSZlSvghCgu75Ne3cyV7U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757593239; c=relaxed/simple; bh=iBaL+C3Xp28K8mC4PWIBs4g6UwkJb0HqUb+c5stSKow=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ECcGL3UJg5fDEWCUkhmjjqF5uBKjrsOpSX9xotSp9kBZfDIItNbhQQpV6Y4nNCmORz2ELIduZaXKttdpIdeVbZSmYqtsOj1hmNJkY40aFVbuAjPCbJJvVXYAROHZ0o+AS3NM6vALU/NTxI+aTMYgnNS4TkwxBWtrgtCFSmO6wOI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=zcxTyi3m; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="zcxTyi3m" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 440A7C4CEF0; Thu, 11 Sep 2025 12:20:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1757593238; bh=iBaL+C3Xp28K8mC4PWIBs4g6UwkJb0HqUb+c5stSKow=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=zcxTyi3mj3xPJKqrnKnIGGAmRJ52Fl13dyR5f7thpAWPqIPXBapi1Nyp4APBTNsup 9w2x2A+6FtYmlSrEyLnn6cVLOBQL/uy0/j4V9syEnv8JxK/l90vTF7LJ6tjKW9zN3C Y3ofwsFf3by7aHhbxogqXAHQ5W7yE88g5R4mPYMs= Date: Thu, 11 Sep 2025 14:20:35 +0200 From: Greg KH To: Wang Tao Cc: stable@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, tglx@linutronix.de, frederic@kernel.org, linux-kernel@vger.kernel.org, tanghui20@huawei.com, zhangqiao22@huawei.com Subject: Re: [PATCH stable/linux-5.10.y] sched/core: Fix potential deadlock on rq lock Message-ID: <2025091123-unsterile-why-ca1e@gregkh> References: <20250908084230.848195-1-wangtao554@huawei.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: <20250908084230.848195-1-wangtao554@huawei.com> On Mon, Sep 08, 2025 at 08:42:30AM +0000, Wang Tao wrote: > When CPU 1 enters the nohz_full state, and the kworker on CPU 0 executes > the function sched_tick_remote, holding the lock on CPU1's rq > and triggering the warning WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3). > This leads to the process of printing the warning message, where the > console_sem semaphore is held. At this point, the print task on the > CPU1's rq cannot acquire the console_sem and joins the wait queue, > entering the UNINTERRUPTIBLE state. It waits for the console_sem to be > released and then wakes up. After the task on CPU 0 releases > the console_sem, it wakes up the waiting console_sem task. > In try_to_wake_up, it attempts to acquire the lock on CPU1's rq again, > resulting in a deadlock. > > The triggering scenario is as follows: > > CPU 0 CPU1 > sched_tick_remote > WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3) > > report_bug con_write > printk > > console_unlock > do_con_write > console_lock > down(&console_sem) > list_add_tail(&waiter.list, &sem->wait_list); > up(&console_sem) > wake_up_q(&wake_q) > try_to_wake_up > __task_rq_lock > _raw_spin_lock > > This patch fixes the issue by deffering all printk console printing > during the lock holding period. > > Fixes: d84b31313ef8 ("sched/isolation: Offload residual 1Hz scheduler tick") > Signed-off-by: Wang Tao > --- > kernel/sched/core.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 40f40f359c5d..fd2c83058ec2 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4091,6 +4091,7 @@ static void sched_tick_remote(struct work_struct *work) > goto out_requeue; > > rq_lock_irq(rq, &rf); > + printk_deferred_enter(); > curr = rq->curr; > if (cpu_is_offline(cpu)) > goto out_unlock; > @@ -4109,6 +4110,7 @@ static void sched_tick_remote(struct work_struct *work) > > calc_load_nohz_remote(rq); > out_unlock: > + printk_deferred_exit(); > rq_unlock_irq(rq, &rf); > out_requeue: > > -- > 2.34.1 > > What is the git commit id of this in Linus's tree? thanks, greg k-h