linux-kernel - Re: [PATCH v4 3/3] rcu: Use _full() API to debug synchronize

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Message-ID: <Z8IKs-I-YsOoS4uw@pc636>
Date: Fri, 28 Feb 2025 20:12:51 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Uladzislau Rezki <urezki@...il.com>, Boqun Feng <boqun.feng@...il.com>,
	RCU <rcu@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Cheung Wall <zzqq0103.hey@...il.com>,
	Neeraj upadhyay <Neeraj.Upadhyay@....com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH v4 3/3] rcu: Use _full() API to debug synchronize_rcu()

Hello, Paul!

> > > > > 
> > > > > Except that I got this from overnight testing of rcu/dev on the shared
> > > > > RCU tree:
> > > > > 
> > > > > WARNING: CPU: 5 PID: 14 at kernel/rcu/tree.c:1636 rcu_sr_normal_complete+0x5c/0x80
> > > > > 
> > > > > I see this only on TREE05.  Which should not be too surprising, given
> > > > > that this is the scenario that tests it.  It happened within five minutes
> > > > > on all 14 of the TREE05 runs.
> > > > > 
> > > > Hm.. This is not fun. I tested this on my system and i did not manage to
> > > > trigger this whereas you do. Something is wrong.
> > > 
> > > If you have a debug patch, I would be happy to give it a go.
> > > 
> > I can trigger it. But.
> > 
> > Some background. I tested those patches during many hours on the stable
> > kernel which is 6.13. On that kernel i was not able to trigger it. Running
> > the rcutorture on the our shared "dev" tree, which i did now, triggers this
> > right away.
> 
> Bisection?  (Hey, you knew that was coming!)
> 
Looks like this: rcu: Fix get_state_synchronize_rcu_full() GP-start detection

After revert in the dev, rcutorture passes TREE05, 16 instances.

--
Uladzislau Rezki