2023-05-02 00:03:36

by Zhouyi Zhou

Subject: [PATCH V2] rcu/torture replace wait_event with wait_event_idle

From: Zhouyi Zhou <[email protected]>

In kfree_rcu_test, kfree_scale_shutdown will be detected as hung task
if kfree_loops is too big. Replace wait_event with wait_event_idle
to avoid false positive.

Tested in the PPC VM of Open Source Lab of Oregon State University.

Suggested-by: Paul E. McKenney <[email protected]>
Signed-off-by: Zhouyi Zhou <[email protected]>
---
kernel/rcu/rcuscale.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index 91fb5905a008..d99c586939d1 100644
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -771,7 +771,7 @@ kfree_scale_cleanup(void)
static int
kfree_scale_shutdown(void *arg)
{
- wait_event(shutdown_wq,
+ wait_event_idle(shutdown_wq,
atomic_read(&n_kfree_scale_thread_ended) >= kfree_nrealthreads);

smp_mb(); /* Wake before output. */
--
2.34.1

2023-05-02 13:43:26

by Paul E. McKenney

Subject: Re: [PATCH V2] rcu/torture replace wait_event with wait_event_idle

On Tue, May 02, 2023 at 08:01:41AM +0800, [email protected] wrote:
> From: Zhouyi Zhou <[email protected]>
>
> In kfree_rcu_test, kfree_scale_shutdown will be detected as hung task
> if kfree_loops is too big. Replace wait_event with wait_event_idle
> to avoid false positive.
>
> Tested in the PPC VM of Open Source Lab of Oregon State University.
>
> Suggested-by: Paul E. McKenney <[email protected]>
> Signed-off-by: Zhouyi Zhou <[email protected]>

Good catch, thank you!

However, this commit beat you to it:

ef1ef3d47677 ("rcuscale: Move shutdown from wait_event() to wait_event_idle()")

Thanx, Paul

> ---
> kernel/rcu/rcuscale.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
> index 91fb5905a008..d99c586939d1 100644
> --- a/kernel/rcu/rcuscale.c
> +++ b/kernel/rcu/rcuscale.c
> @@ -771,7 +771,7 @@ kfree_scale_cleanup(void)
> static int
> kfree_scale_shutdown(void *arg)
> {
> - wait_event(shutdown_wq,
> + wait_event_idle(shutdown_wq,
> atomic_read(&n_kfree_scale_thread_ended) >= kfree_nrealthreads);
>
> smp_mb(); /* Wake before output. */
> --
> 2.34.1
>

2023-05-02 13:55:11

by Zhouyi Zhou

Subject: Re: [PATCH V2] rcu/torture replace wait_event with wait_event_idle

On Tue, May 2, 2023 at 9:40 PM Paul E. McKenney <[email protected]> wrote:
>
> On Tue, May 02, 2023 at 08:01:41AM +0800, [email protected] wrote:
> > From: Zhouyi Zhou <[email protected]>
> >
> > In kfree_rcu_test, kfree_scale_shutdown will be detected as hung task
> > if kfree_loops is too big. Replace wait_event with wait_event_idle
> > to avoid false positive.
> >
> > Tested in the PPC VM of Open Source Lab of Oregon State University.
> >
> > Suggested-by: Paul E. McKenney <[email protected]>
> > Signed-off-by: Zhouyi Zhou <[email protected]>
>
> Good catch, thank you!
>
> However, this commit beat you to it:
>
> ef1ef3d47677 ("rcuscale: Move shutdown from wait_event() to wait_event_idle()")
You are very welcome ;-) Still, this is a very fruitful learning
process for me ;-)

Cheers
Zhouyi
>
> Thanx, Paul
>
> > ---
> > kernel/rcu/rcuscale.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
> > index 91fb5905a008..d99c586939d1 100644
> > --- a/kernel/rcu/rcuscale.c
> > +++ b/kernel/rcu/rcuscale.c
> > @@ -771,7 +771,7 @@ kfree_scale_cleanup(void)
> > static int
> > kfree_scale_shutdown(void *arg)
> > {
> > - wait_event(shutdown_wq,
> > + wait_event_idle(shutdown_wq,
> > atomic_read(&n_kfree_scale_thread_ended) >= kfree_nrealthreads);
> >
> > smp_mb(); /* Wake before output. */
> > --
> > 2.34.1
> >