linux-kernel - Re: [PATCH 2/3] rcu: Defer RCU kthreads wakeup when CPU is dying

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <65b6b97a6f61f80c5f1ea1f245eea392a0de5523.camel@mediatek.com>
Date: Mon, 12 Aug 2024 09:10:56 +0000
From: Cheng-Jui Wang (王正睿)
	<Cheng-Jui.Wang@...iatek.com>
To: "frederic@...nel.org" <frederic@...nel.org>, "qiang.zhang1211@...il.com"
	<qiang.zhang1211@...il.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"peterz@...radead.org" <peterz@...radead.org>, "tglx@...utronix.de"
	<tglx@...utronix.de>, "neeraj.upadhyay@....com" <neeraj.upadhyay@....com>,
	"paulmck@...nel.org" <paulmck@...nel.org>,
	Bobule Chang (張弘義) <bobule.chang@...iatek.com>,
	"boqun.feng@...il.com" <boqun.feng@...il.com>, "urezki@...il.com"
	<urezki@...il.com>, "joel@...lfernandes.org" <joel@...lfernandes.org>,
	"rcu@...r.kernel.org" <rcu@...r.kernel.org>
Subject: Re: [PATCH 2/3] rcu: Defer RCU kthreads wakeup when CPU is dying

On Wed, 2023-12-20 at 16:13 +0100, Frederic Weisbecker wrote:
> Le Wed, Dec 20, 2023 at 04:24:35PM +0800, Z qiang a écrit :
> > > 
> > 
> > In the rcutree_report_cpu_dead(), the rcuog kthreads may also be
> > wakeup in
> > do_nocb_deferred_wakeup(), if the rcuog kthreads is rt-fifo and
> > wakeup happen,
> > the rt_period_active is set 1 and enqueue hrtimer to offline CPU in
> > do_start_rt_bandwidth(),
> > after that, we invoke swake_up_one_online() send ipi to online CPU,
> > due to the
> > rt_period_active is 1, the rt-bandwith hrtimer will not enqueue to
> > online CPU.
> > any thoughts?
> 
> Duh, you're right, that one too. How many more? This hrtimer
> situation is scary...
> 
> Thanks.

I encountered the issue pointed out by Z Qiang on kernel-6.6, which
cause RT tasks on the CPU to never be scheduled, leading to a system
reboot. It triggered the WARN_ON_ONCE(!base->cpu_base->online)
introduced in [PATCH 1/3]. Below is the call trace:

 Call trace:
  enqueue_hrtimer+0x7c/0xf8
  hrtimer_start_range_ns+0x2b8/0x300
  enqueue_task_rt+0x298/0x3f0
  enqueue_task+0x94/0x188
  ttwu_do_activate+0xb4/0x27c
  try_to_wake_up+0x2d8/0x79c
  wake_up_process+0x18/0x28
  __wake_nocb_gp+0x80/0x1a0
  do_nocb_deferred_wakeup_common+0x3c/0xcc
  rcu_report_dead+0x68/0x1ac
  cpuhp_report_idle_dead+0x48/0x9c
  do_idle+0x288/0x294
  cpu_startup_entry+0x34/0x3c
  secondary_start_kernel+0x138/0x158