Re: [PATCH] rcutorture: Clear cbflood_max for tasks-rude and srcu-atomic testing

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

> 
> On 12 October 2026 11:41:34 BST, Zqiang <qiang.zhang@linux.dev> 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
> > removes the .cbflood_max from tasks-rude and clears ->cbflood_max in the
> > srcu_torture_init_forbidden_apis().
> > 
> > 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
> > 
> Fixes tag?
> 
> This LGTM anyway so:
> 
> Reviewed-by: Bradley Morgan <brads@mainlining.org>

Thanks for reviewed !!

Thanks
Zqiang

> 
> > 
> > Signed-off-by: Zqiang <qiang.zhang@linux.dev>
> > ---
> >  kernel/rcu/rcutorture.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> > index 968343be4e0d..00db87256e78 100644
> > --- a/kernel/rcu/rcutorture.c
> > +++ b/kernel/rcu/rcutorture.c
> > @@ -723,6 +723,7 @@ static void srcu_torture_init_forbidden_apis(void)
> >  cur_ops->deferred_free = NULL;
> >  cur_ops->exp_current = NULL;
> >  cur_ops->start_gp_poll = NULL;
> > + cur_ops->cbflood_max = 0;
> >  }
> >  
> >  static void srcu_torture_init(void)
> > @@ -1250,7 +1251,6 @@ static struct rcu_torture_ops tasks_rude_ops = {
> >  .exp_sync = synchronize_rcu_tasks_rude,
> >  .gp_kthread_dbg = show_rcu_tasks_rude_gp_kthread,
> >  .get_gp_data = rcu_tasks_rude_get_gp_data,
> > - .cbflood_max = 50000,
> >  .irq_capable = 1,
> >  .name = "tasks-rude"
> >  };
> > 
> --- Thanks!
> "I'm not a very positive person" - Linus torvalds
>