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From: Peter Zijlstra <peterz@infradead.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] sched: Switch wait_task_inactive to HRTIMER_MODE_REL_HARD
Date: Thu, 26 Aug 2021 19:14:06 +0200	[thread overview]
Message-ID: <YSfL3vdbuXWvI/Ya@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210826170408.vm7rlj7odslshwch@linutronix.de>

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@linutronix.de>

Thanks!

  reply	other threads:[~2021-08-26 17:14 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-26 17:04 [PATCH] sched: Switch wait_task_inactive to HRTIMER_MODE_REL_HARD Sebastian Andrzej Siewior
2021-08-26 17:14 ` Peter Zijlstra [this message]
2021-09-09 11:18 ` [tip: sched/core] " tip-bot2 for Sebastian Andrzej Siewior
2021-10-05 14:12 ` tip-bot2 for Sebastian Andrzej Siewior

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