Re: [PATCH v2] rcutorture: Avoid create fwd_prog_tasks for tasks-rude and srcu-atomic

["Zqiang" <qiang.zhang@linux.dev>]

> 
> > 
> > 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.


Hello, Joel

I have make simple testing for all rcu flavor:

rcu:

[    3.871868][  T158] rcu-torture: rcu_torture_fwd_progress task started
[    3.874347][    T1] tasks-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test
[    3.862128][    T1] tasks-tracing-torture: Creating rcu_torture_fwd_prog task
[    3.857800][    T1] tasks-rude-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test
[    3.435733][    T1] busted-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test

srcu:

[    3.676067][    T1] srcu-torture: srcu_torture_init normal SRCU
[    3.691425][    T1] srcu-torture: Creating rcu_torture_fwd_prog task

[    3.467289][    T1] srcu-torture: srcu_torture_init NMI-safe SRCU
[    3.482983][    T1] srcu-torture: Creating rcu_torture_fwd_prog task

[    3.457597][    T1] srcu-torture: srcu_torture_init fast SRCU
[    3.475676][    T1] srcu-torture: Creating rcu_torture_fwd_prog task

[    3.381378][    T1] srcu-torture: srcu_torture_init fast-up/down SRCU
[    3.397417][    T1] srcu-torture: Creating rcu_torture_fwd_prog task

[    3.479642][    T1] srcu-torture: srcu_torture_init atomic SRCU
[    3.488532][    T1] srcu-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test

srcud:

[    3.898271][    T1] srcud-torture: srcud_torture_init normal SRCU
[    3.915141][    T1] srcud-torture: Creating rcu_torture_fwd_prog task

[    3.586829][    T1] srcud-torture: srcud_torture_init NMI-safe SRCU
[    3.604943][  T146] srcud-torture: rcu_torture_fwd_progress task started

[    3.617095][    T1] srcud-torture: srcud_torture_init fast SRCU
[    3.635608][    T1] srcud-torture: Creating rcu_torture_fwd_prog task

[    3.915194][    T1] srcud-torture: srcud_torture_init fast-up/down SRCU
[    3.933086][    T1] srcud-torture: Creating rcu_torture_fwd_prog task

[    3.866575][    T1] srcud-torture: srcud_torture_init atomic SRCU
[    3.883949][    T1] srcud-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test

srcud-busted:

[    3.382474][    T1] busted_srcud-torture: srcu_torture_init normal SRCU
[    3.389525][    T1] busted_srcud-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test

[    3.423111][    T1] busted_srcud-torture: srcu_torture_init NMI-safe SRCU
[    3.432941][    T1] busted_srcud-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test

[    3.364002][    T1] busted_srcud-torture: srcu_torture_init fast SRCU
[    3.372654][    T1] busted_srcud-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test

[    3.860358][    T1] busted_srcud-torture: srcu_torture_init fast-up/down SRCU
[    3.870796][    T1] busted_srcud-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test

[    3.364909][    T1] busted_srcud-torture: srcu_torture_init atomic SRCU
[    3.372280][    T1] busted_srcud-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test

trivial:

[    3.858080][    T1] trivial-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test
[    3.689060][    T1] trivial-preempt-torture: rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test



Thanks
Zqiang

> 
> 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
> >  
> > 
> > > 
> > > 
> > >
> >
>