linux-kernel - Re: [PATCH v2 3/3] rcu: Use _full() API to debug synchronize

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Message-ID: <Z72hZg323iI3P8B4@pc636>
Date: Tue, 25 Feb 2025 11:54:30 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: "Uladzislau Rezki (Sony)" <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 v2 3/3] rcu: Use _full() API to debug synchronize_rcu()

On Mon, Feb 24, 2025 at 11:06:01AM -0800, Paul E. McKenney wrote:
> On Mon, Feb 24, 2025 at 02:36:59PM +0100, Uladzislau Rezki (Sony) wrote:
> > Switch for using of get_state_synchronize_rcu_full() and
> > poll_state_synchronize_rcu_full() pair for debug a normal
> > synchronize_rcu() call.
> > 
> > Just using "not" full APIs to identify if a grace period
> > is passed or not might lead to a false kernel splat.
> > 
> > Link: https://lore.kernel.org/lkml/Z5ikQeVmVdsWQrdD@pc636/T/
> > Fixes: 988f569ae041 ("rcu: Reduce synchronize_rcu() latency")
> > Reported-by: cheung wall <zzqq0103.hey@...il.com>
> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> > ---
> >  include/linux/rcupdate_wait.h | 4 ++++
> >  kernel/rcu/tree.c             | 8 +++-----
> >  2 files changed, 7 insertions(+), 5 deletions(-)
> > 
> > diff --git a/include/linux/rcupdate_wait.h b/include/linux/rcupdate_wait.h
> > index f9bed3d3f78d..a16fc2a9a7d7 100644
> > --- a/include/linux/rcupdate_wait.h
> > +++ b/include/linux/rcupdate_wait.h
> > @@ -16,6 +16,10 @@
> >  struct rcu_synchronize {
> >  	struct rcu_head head;
> >  	struct completion completion;
> > +#ifdef CONFIG_PROVE_RCU
> > +	/* This is for testing. */
> > +	struct rcu_gp_oldstate oldstate;
> > +#endif
> 
> This causes the build to fail on TREE01.  One way to make the build
> succeed is to remove the #ifdefs above.  Another way would be to add
> #ifdefs to the WARN_ONCE() below.  I suspect that removing the #ifdefs
> is best, at least until such time as people start passing many tens
> of SRCU instances to synchronize_rcu_mult() or some such (which seems
> quite unlikely).
> 
> Thoughts?
> 
Right, i agree. I will repost this series.

Thank you for checking and testing :)

--
Uladzislau Rezki