linux-kernel - Re: [BUG?] INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 0-.... } 3 jiffies s: 309 root: 0x1/.

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Date:   Thu, 13 Apr 2023 09:21:10 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Rui Salvaterra <rsalvaterra@...il.com>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>, rodrigo.vivi@...el.com,
        tvrtko.ursulin@...ux.intel.com, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [BUG?] INFO: rcu_sched detected expedited stalls on CPUs/tasks:
 { 0-.... } 3 jiffies s: 309 root: 0x1/.

On Thu, Apr 13, 2023 at 04:32:32PM +0100, Rui Salvaterra wrote:
> Hi, Paul,
> 
> On Thu, 13 Apr 2023 at 15:43, Paul E. McKenney <paulmck@...nel.org> wrote:
> >
> > My guess would be that you have CONFIG_RCU_EXP_CPU_STALL_TIMEOUT set to
> > some small non-zero number, for example, you might have set up a recent
> > Android .config or some such.  The default of zero would give you about
> > 21 seconds rather than the three jiffies that you are seeing.
> >
> > Could you please check your .config?
> 
> Well, this is embarrassing. I can't fathom why/how, but I had it set
> to 20, on this machine. That is, 20 millisseconds. I guess its a
> miracle I haven't seen *more* expedited RCU traces. Sorry for the
> noise, everyone.

Been there, done that!

And actually, it is kind of reassuring that the Linux kernel avoids
tens-of-milliseocnds latency blows in the common case on your system.

						Thanx, Paul