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Date:   Mon, 23 Mar 2020 17:06:10 +0000
From:   Qais Yousef <qais.yousef@arm.com>
To:     "Paul E. McKenney" <paulmck@kernel.org>
Cc:     Davidlohr Bueso <dave@stgolabs.net>,
        Josh Triplett <josh@joshtriplett.org>,
        linux-kernel@vger.kernel.org
Subject: Re: Hit WARN_ON() in rcutorture.c:1055
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On 03/23/20 08:57, Paul E. McKenney wrote:
> On Mon, Mar 23, 2020 at 03:43:09PM +0000, Qais Yousef wrote:
> > Hi
> > 
> > I hit the following warning while running rcutorture tests. It only happens
> > when I try to hibernate the system (arm64 Juno-r2).
> 
> Hibernating the system during rcutorture tests.  Now that is gutsy!  ;-)

Hehe was just a side effect of testing the cpu hotplug stuff :-)

> 
> > Let me know if you need additional info.
> 
> 1.	Do you need this to work?  If so, please tell me your use case.

Nope. It just happened while trying to stress the cpu hotplug series I just
posted.

> 
> 2.	What is line 1055 of your rcutorture.c?  Here is my guess:

It's 5.6-rc6, sorry should have mentioned in the report.

		/* Cycle through nesting levels of rcu_expedite_gp() calls. */
		if (can_expedite &&
		    !(torture_random(&rand) & 0xff & (!!expediting - 1))) {
			WARN_ON_ONCE(expediting == 0 && rcu_gp_is_expedited());
			if (expediting >= 0)
				rcu_expedite_gp();
			else
				rcu_unexpedite_gp();
			if (++expediting > 3)
				expediting = -expediting;
		} else if (!can_expedite) { /* Disabled during boot, recheck. */

If it's something you don't care about, then I don't care about too. I just
thought I'd report it in case it uncovered something worthwhile.

Thanks!

--
Qais Yousef