* Re: [PATCH v2] rcutorture: Avoid create fwd_prog_tasks for tasks-rude and srcu-atomic
@ 2026-10-30 12:46 Joel Fernandes
0 siblings, 0 replies; 4+ messages in thread
From: Joel Fernandes @ 2026-10-30 12:46 UTC (permalink / raw)
To: Zqiang
Cc: paulmck, frederic, neeraj.upadhyay, urezki, boqun, rcu, linux-kernel
> On Oct 30, 2026, at 8:14 AM, Zqiang <qiang.zhang@linux.dev> wrote:
>
>
>>
>>
>>> On Fri, Oct 23, 2026 at 05:37:16PM +0800, Zqiang wrote:
>>>
>>>
>>> When running the tasks-rude and srcu-atomic tests, the fwd_prog_tasks
>>> kthread is created because the default value of fwd_progress is 1.
>>> however, the two RCU flavors not support ->call():
>>>
>>> 1. tasks-rude: commit b428a9de9bba ("rcutorture: Stop testing RCU Tasks
>>> Rude asynchronous APIs") removed .call and .cb_barrier from tasks-rude,
>>> but left the .cbflood_max = 50000.
>>>
>>> 2. srcu-atomic: srcu_torture_init_forbidden_apis() sets ->call to NULL
>>> for SRCU_READ_FLAVOR_ATOMIC runs, but leaves ->cbflood_max untouched.
>>>
>>> In both cases, the non-zero ->cbflood_max fools the check above into
>>> creating the fwd_prog_tasks kthreads, even though those kthreads cannot
>>> possibly carry out any forward-progress test:
>>>
>>> 1. The rcu_torture_fwd_prog_cr() returns immediately due to cur_ops->call
>>> is NULL:
>>>
>>> [ 68.022674] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
>>> [ 129.462046] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
>>> [ 190.902123] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
>>> [ 252.343809] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
>>>
>>> 2. The rcu_torture_fwd_prog_nr() is never even invoked, because its caller
>>> requires cur_ops->stall_dur, and neither tasks-rude nor srcu-atomic
>>> provide ->stall_dur (only rcu_ops does).
>>>
>>> Therefore, creating fwd_prog_tasks kthreads is pointless, this commit adds
>>> ->call and ->cb_barrier to the forward-progress check, rejecting flavors
>>> that lack the cbflood_max set and a positive ->stall_dur.
>>>
>>> simple verification output:
>>>
>>> [ 3.062959][ T1] srcu-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test
>>> [ 2.922323][ T1] tasks-rude-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test
>>>
>>> Suggested-by: Joel Fernandes <joelagnelf@nvidia.com>
>>> Signed-off-by: Zqiang <qiang.zhang@linux.dev>
>>>
>> Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
>>
>> It would nevertheless be good to run tests demonstrating that
>> forward-progress testing happens and does not happen on the same
>> rcu_torture_ops structures as before. Just in case I lost my
>> way through that boolean expression. ;-)
>
> Ok, I see. thanks Paul ;-) .
So let me know Zqiang once you are confident on the testing from and I will apply it for 7.5.
thanks,
Joel Fernandes
>
>>
>>>
>>> ---
>>> kernel/rcu/rcutorture.c | 5 ++---
>>> 1 file changed, 2 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
>>> index 968343be4e0d..92ff197f4789 100644
>>> --- a/kernel/rcu/rcutorture.c
>>> +++ b/kernel/rcu/rcutorture.c
>>> @@ -4007,9 +4007,8 @@ static int __init rcu_torture_fwd_prog_init(void)
>>> } else if (fwd_progress < 0) {
>>> fwd_progress = nr_cpu_ids;
>>> }
>>> - if ((!cur_ops->sync && !cur_ops->call) ||
>>> - (!cur_ops->cbflood_max && (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0)) ||
>>> - cur_ops == &rcu_busted_ops) {
>>> + if (!cur_ops->sync || ((!cur_ops->call || !cur_ops->cb_barrier || !cur_ops->cbflood_max) &&
>>> + (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0))) {
>>> VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test");
>>> fwd_progress = 0;
>>> return 0;
>>> --
>>> 2.17.1
>>>
>>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] rcutorture: Avoid create fwd_prog_tasks for tasks-rude and srcu-atomic
2026-10-23 19:23 ` Paul E. McKenney
@ 2026-10-30 12:14 ` Zqiang
0 siblings, 0 replies; 4+ messages in thread
From: Zqiang @ 2026-10-30 12:14 UTC (permalink / raw)
To: paulmck
Cc: frederic, neeraj.upadhyay, joelagnelf, urezki, boqun, rcu, linux-kernel
>
> On Fri, Oct 23, 2026 at 05:37:16PM +0800, Zqiang wrote:
>
> >
> > When running the tasks-rude and srcu-atomic tests, the fwd_prog_tasks
> > kthread is created because the default value of fwd_progress is 1.
> > however, the two RCU flavors not support ->call():
> >
> > 1. tasks-rude: commit b428a9de9bba ("rcutorture: Stop testing RCU Tasks
> > Rude asynchronous APIs") removed .call and .cb_barrier from tasks-rude,
> > but left the .cbflood_max = 50000.
> >
> > 2. srcu-atomic: srcu_torture_init_forbidden_apis() sets ->call to NULL
> > for SRCU_READ_FLAVOR_ATOMIC runs, but leaves ->cbflood_max untouched.
> >
> > In both cases, the non-zero ->cbflood_max fools the check above into
> > creating the fwd_prog_tasks kthreads, even though those kthreads cannot
> > possibly carry out any forward-progress test:
> >
> > 1. The rcu_torture_fwd_prog_cr() returns immediately due to cur_ops->call
> > is NULL:
> >
> > [ 68.022674] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
> > [ 129.462046] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
> > [ 190.902123] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
> > [ 252.343809] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
> >
> > 2. The rcu_torture_fwd_prog_nr() is never even invoked, because its caller
> > requires cur_ops->stall_dur, and neither tasks-rude nor srcu-atomic
> > provide ->stall_dur (only rcu_ops does).
> >
> > Therefore, creating fwd_prog_tasks kthreads is pointless, this commit adds
> > ->call and ->cb_barrier to the forward-progress check, rejecting flavors
> > that lack the cbflood_max set and a positive ->stall_dur.
> >
> > simple verification output:
> >
> > [ 3.062959][ T1] srcu-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test
> > [ 2.922323][ T1] tasks-rude-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test
> >
> > Suggested-by: Joel Fernandes <joelagnelf@nvidia.com>
> > Signed-off-by: Zqiang <qiang.zhang@linux.dev>
> >
> Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
>
> It would nevertheless be good to run tests demonstrating that
> forward-progress testing happens and does not happen on the same
> rcu_torture_ops structures as before. Just in case I lost my
> way through that boolean expression. ;-)
Ok, I see. thanks Paul ;-) .
>
> >
> > ---
> > kernel/rcu/rcutorture.c | 5 ++---
> > 1 file changed, 2 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> > index 968343be4e0d..92ff197f4789 100644
> > --- a/kernel/rcu/rcutorture.c
> > +++ b/kernel/rcu/rcutorture.c
> > @@ -4007,9 +4007,8 @@ static int __init rcu_torture_fwd_prog_init(void)
> > } else if (fwd_progress < 0) {
> > fwd_progress = nr_cpu_ids;
> > }
> > - if ((!cur_ops->sync && !cur_ops->call) ||
> > - (!cur_ops->cbflood_max && (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0)) ||
> > - cur_ops == &rcu_busted_ops) {
> > + if (!cur_ops->sync || ((!cur_ops->call || !cur_ops->cb_barrier || !cur_ops->cbflood_max) &&
> > + (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0))) {
> > VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test");
> > fwd_progress = 0;
> > return 0;
> > --
> > 2.17.1
> >
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] rcutorture: Avoid create fwd_prog_tasks for tasks-rude and srcu-atomic
2026-10-23 9:37 Zqiang
@ 2026-10-23 19:23 ` Paul E. McKenney
2026-10-30 12:14 ` Zqiang
0 siblings, 1 reply; 4+ messages in thread
From: Paul E. McKenney @ 2026-10-23 19:23 UTC (permalink / raw)
To: Zqiang
Cc: frederic, neeraj.upadhyay, joelagnelf, urezki, boqun, rcu, linux-kernel
On Fri, Oct 23, 2026 at 05:37:16PM +0800, Zqiang wrote:
> When running the tasks-rude and srcu-atomic tests, the fwd_prog_tasks
> kthread is created because the default value of fwd_progress is 1.
> however, the two RCU flavors not support ->call():
>
> 1. tasks-rude: commit b428a9de9bba ("rcutorture: Stop testing RCU Tasks
> Rude asynchronous APIs") removed .call and .cb_barrier from tasks-rude,
> but left the .cbflood_max = 50000.
>
> 2. srcu-atomic: srcu_torture_init_forbidden_apis() sets ->call to NULL
> for SRCU_READ_FLAVOR_ATOMIC runs, but leaves ->cbflood_max untouched.
>
> In both cases, the non-zero ->cbflood_max fools the check above into
> creating the fwd_prog_tasks kthreads, even though those kthreads cannot
> possibly carry out any forward-progress test:
>
> 1. The rcu_torture_fwd_prog_cr() returns immediately due to cur_ops->call
> is NULL:
>
> [ 68.022674] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
> [ 129.462046] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
> [ 190.902123] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
> [ 252.343809] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
>
> 2. The rcu_torture_fwd_prog_nr() is never even invoked, because its caller
> requires cur_ops->stall_dur, and neither tasks-rude nor srcu-atomic
> provide ->stall_dur (only rcu_ops does).
>
> Therefore, creating fwd_prog_tasks kthreads is pointless, this commit adds
> ->call and ->cb_barrier to the forward-progress check, rejecting flavors
> that lack the cbflood_max set and a positive ->stall_dur.
>
> simple verification output:
>
> [ 3.062959][ T1] srcu-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test
> [ 2.922323][ T1] tasks-rude-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test
>
> Suggested-by: Joel Fernandes <joelagnelf@nvidia.com>
> Signed-off-by: Zqiang <qiang.zhang@linux.dev>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
It would nevertheless be good to run tests demonstrating that
forward-progress testing happens and does not happen on the same
rcu_torture_ops structures as before. Just in case I lost my
way through that boolean expression. ;-)
> ---
> kernel/rcu/rcutorture.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 968343be4e0d..92ff197f4789 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -4007,9 +4007,8 @@ static int __init rcu_torture_fwd_prog_init(void)
> } else if (fwd_progress < 0) {
> fwd_progress = nr_cpu_ids;
> }
> - if ((!cur_ops->sync && !cur_ops->call) ||
> - (!cur_ops->cbflood_max && (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0)) ||
> - cur_ops == &rcu_busted_ops) {
> + if (!cur_ops->sync || ((!cur_ops->call || !cur_ops->cb_barrier || !cur_ops->cbflood_max) &&
> + (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0))) {
> VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test");
> fwd_progress = 0;
> return 0;
> --
> 2.17.1
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH v2] rcutorture: Avoid create fwd_prog_tasks for tasks-rude and srcu-atomic
@ 2026-10-23 9:37 Zqiang
2026-10-23 19:23 ` Paul E. McKenney
0 siblings, 1 reply; 4+ messages in thread
From: Zqiang @ 2026-10-23 9:37 UTC (permalink / raw)
To: paulmck, frederic, neeraj.upadhyay, joelagnelf, urezki, boqun
Cc: qiang.zhang, rcu, linux-kernel
When running the tasks-rude and srcu-atomic tests, the fwd_prog_tasks
kthread is created because the default value of fwd_progress is 1.
however, the two RCU flavors not support ->call():
1. tasks-rude: commit b428a9de9bba ("rcutorture: Stop testing RCU Tasks
Rude asynchronous APIs") removed .call and .cb_barrier from tasks-rude,
but left the .cbflood_max = 50000.
2. srcu-atomic: srcu_torture_init_forbidden_apis() sets ->call to NULL
for SRCU_READ_FLAVOR_ATOMIC runs, but leaves ->cbflood_max untouched.
In both cases, the non-zero ->cbflood_max fools the check above into
creating the fwd_prog_tasks kthreads, even though those kthreads cannot
possibly carry out any forward-progress test:
1. The rcu_torture_fwd_prog_cr() returns immediately due to cur_ops->call
is NULL:
[ 68.022674] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
[ 129.462046] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
[ 190.902123] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
[ 252.343809] rcu_torture_fwd_prog_cr: No ->call(), so no forward-progress test 0
2. The rcu_torture_fwd_prog_nr() is never even invoked, because its caller
requires cur_ops->stall_dur, and neither tasks-rude nor srcu-atomic
provide ->stall_dur (only rcu_ops does).
Therefore, creating fwd_prog_tasks kthreads is pointless, this commit adds
->call and ->cb_barrier to the forward-progress check, rejecting flavors
that lack the cbflood_max set and a positive ->stall_dur.
simple verification output:
[ 3.062959][ T1] srcu-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test
[ 2.922323][ T1] tasks-rude-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test
Suggested-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Zqiang <qiang.zhang@linux.dev>
---
kernel/rcu/rcutorture.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 968343be4e0d..92ff197f4789 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -4007,9 +4007,8 @@ static int __init rcu_torture_fwd_prog_init(void)
} else if (fwd_progress < 0) {
fwd_progress = nr_cpu_ids;
}
- if ((!cur_ops->sync && !cur_ops->call) ||
- (!cur_ops->cbflood_max && (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0)) ||
- cur_ops == &rcu_busted_ops) {
+ if (!cur_ops->sync || ((!cur_ops->call || !cur_ops->cb_barrier || !cur_ops->cbflood_max) &&
+ (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0))) {
VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test");
fwd_progress = 0;
return 0;
--
2.17.1
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2026-10-30 12:47 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2026-10-30 12:46 [PATCH v2] rcutorture: Avoid create fwd_prog_tasks for tasks-rude and srcu-atomic Joel Fernandes
-- strict thread matches above, loose matches on Subject: below --
2026-10-23 9:37 Zqiang
2026-10-23 19:23 ` Paul E. McKenney
2026-10-30 12:14 ` Zqiang
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
all inboxes | Powered by JetHome®