linux-kernel - Re: [PATCH] sched: Switch wait_task_inactive to HRTIMER_MODE_REL

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: <YSfL3vdbuXWvI/Ya@hirez.programming.kicks-ass.net>
Date:   Thu, 26 Aug 2021 19:14:06 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sched: Switch wait_task_inactive to HRTIMER_MODE_REL_HARD

On Thu, Aug 26, 2021 at 07:04:08PM +0200, Sebastian Andrzej Siewior wrote:
> With PREEMPT_RT enabled all hrtimers callbacks will be invoked in
> softirq mode unless they are explicitly marked as HRTIMER_MODE_HARD.
> During boot kthread_bind() is used for the creation of per-CPU threads
> and then hangs in wait_task_inactive() if the ksoftirqd is not
> yet up and running.
> The hang disappeared since commit
>    26c7295be0c5e ("kthread: Do not preempt current task if it is going to call schedule()")
> 
> but enabling function trace on boot reliably leads to the freeze on boot
> behaviour again.
> The timer in wait_task_inactive() can not be directly used by a user
> interface to abuse it and create a mass wake up of several tasks at the
> same time leading to long sections with disabled interrupts.
> Therefore it is safe to make the timer HRTIMER_MODE_REL_HARD.
> 
> Switch the timer to HRTIMER_MODE_REL_HARD.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Thanks!