linux-kernel - Re: [Regression] wifi problems since tg3 started throwing rcu stall warnings

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Message-ID: <Zzxr72hkv8DAwjMG@pavilion.home>
Date: Tue, 19 Nov 2024 11:43:59 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Mingcong Bai <jeffbai@...c.io>
Cc: "Paul E. McKenney" <paulmck@...nel.org>,
	Thorsten Leemhuis <regressions@...mhuis.info>,
	Linux regressions mailing list <regressions@...ts.linux.dev>,
	LKML <linux-kernel@...r.kernel.org>, rcu <rcu@...r.kernel.org>,
	sakiiily@...c.io, Kexy Biscuit <kexybiscuit@...c.io>
Subject: Re: [Regression] wifi problems since tg3 started throwing rcu stall
 warnings

Le Fri, Nov 15, 2024 at 11:01:25AM +0800, Mingcong Bai a écrit :
> Hi Frederic,
> 
> <snip>
> 
> > Just in case, Mingcong Bai can you test the following patch without the
> > revert and see if it triggers something?
> > 
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 35949ec1f935..b4f8ed8138d3 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -5170,6 +5170,7 @@ void rcutree_migrate_callbacks(int cpu)
> >  	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
> >  	bool needwake;
> > 
> > +	WARN_ON_ONCE(1);
> >  	if (rcu_rdp_is_offloaded(rdp))
> >  		return;
> > 
> 
> Please find attached the dmesg with your patch (and no revert) against
> 6.12-rc7.

The added WARN_ON_ONCE() doesn't trigger so the function/path changed by this patch
isn't taken.

My only guess is that the patch changes some code layout that makes a bug more
likely to appear in networking...

Thanks.

> 
> Best Regards,
> Mingcong Bai
> 
> > 
> > 
> > Thanks.
> > 
> > > 
> > > 							Thanx, Paul