linux-kernel - Re: [PATCH] rcutorture: Replace schedule_timeout*() 1 jiffie waits with HZ/20

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Date:   Fri, 25 Aug 2023 02:55:38 +0000
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
        Josh Triplett <josh@...htriplett.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Zqiang <qiang.zhang1211@...il.com>, rcu@...r.kernel.org
Subject: Re: [PATCH] rcutorture: Replace schedule_timeout*() 1 jiffie waits
 with HZ/20

On Wed, Aug 23, 2023 at 02:07:55PM -0700, Paul E. McKenney wrote:
> On Wed, Aug 16, 2023 at 08:49:12PM +0000, Joel Fernandes (Google) wrote:
> > In the past, we see that spinning on schedule_timeout* with a wait of 1
> > jiffie can hang the kernel. See d52d3a2bf408 ("torture: Fix hang during
> > kthread shutdown phase").
> > 
> > Recently again it showed up in torture's stutter code as well. The behavior is
> > the the function may instantly return and never go to sleep preempting whatever
> > was running under it.
> > 
> > To prevent future issues, apply the same fix mentioned in the above
> > commit d52d3a2bf408 to more places.
> > 
> > I took care to only apply it to places where I thought it made sense.
> > 
> > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> 
> Hearing no objections, I applied this for further review and testing.
> 
> In the future, should some of these become hrtimers?

Yes they certainly could be but we don't need these ones to be high
resolution AFAICS and the jiffie granularity should be good.

thanks,

 - Joel