[PATCH RT 4.19] rcutorture: Fix oops when selecting non-default torture_type

[PATCH RT 4.19] rcutorture: Fix oops when selecting non-default torture_type

[Scott Wood]

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@redhat.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).

 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
 
-- 
2.18.1

Re: [PATCH RT 4.19] rcutorture: Fix oops when selecting non-default torture_type

[Sebastian Andrzej Siewior]

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@redhat.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

Re: [PATCH RT 4.19] rcutorture: Fix oops when selecting non-default torture_type

[Paul E. McKenney]

On Thu, Mar 21, 2019 at 10:21:21PM -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@redhat.com>

This rcu_bh torture type is gone completely in mainline, however,
I just yesterday queued a patch to fix some problems when an invalid
torture_type was specified.

Mainline 4.19 does have the .name element of rcu_bh_ops specified,
though.  Not sure what happened here, but you are absolutely
correct that rcu_bh_ops does need a .name initializer.

							Thanx, Paul

> ---
> 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).
> 
>  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
> 
> -- 
> 2.18.1
>