linux-kernel - Re: [PATCH RT 4.19] rcutorture: Fix oops when selecting non-default torture

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Message-ID: <20190322092244.4nthhso5onp426zy@linutronix.de>
Date:   Fri, 22 Mar 2019 10:22:44 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Scott Wood <swood@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Juri Lelli <juri.lelli@...hat.com>, anna-maria@...utronix.de,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH RT 4.19] rcutorture: Fix oops when selecting non-default
 torture_type

On 2019-03-21 22:21:21 [-0500], Scott Wood wrote:
> rcu_bh is disabled on PREEMPT_RT via a stub ops that has no name.  Thus,
> if a torture_type other than "rcu" is used, rcu_torture_init() will
> pass NULL to strcmp() when iterating over torture_ops[], and oops.
> 
> Signed-off-by: Scott Wood <swood@...hat.com>
> ---
> With this applied to 4.19.25-rt16 and specifying torture_type=sched,
> similar rcutorture failures are seen as with 5.0.3-rt1 (in which standard
> torture_cype=rcu no longer has .extendables=0 and thus stresses similar
> paths).

Anna-Maria was talking about this to me a long time ago, I though we
fixed that. But since your patch targets v4.19 it is not the case.
As far v4.19 goes, I think it can go in but this is up to Steven now.

Does this still apply to 5.0-RT? The RCU was greatly reworked so it may
no longer apply and just work. However the "random context" in
rcutorture gives me a headache right now…

>  kernel/rcu/rcutorture.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 7d2a615601e7..408d03048911 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -479,6 +479,7 @@ static struct rcu_torture_ops rcu_bh_ops = {
>  #else
>  static struct rcu_torture_ops rcu_bh_ops = {
>  	.ttype		= INVALID_RCU_FLAVOR,
> +	.name		= "rcu_bh"
>  };
>  #endif
>  

Sebastian