Re: [PATCH v2] rcutorture: Avoid create fwd_prog_tasks for tasks-rude and srcu-atomic
From: Zqiang
Date: Mon Nov 02 2026 - 08:54:38 EST
>
> >
> > On Oct 30, 2026, at 8:14 AM, Zqiang <qiang.zhang@xxxxxxxxx> 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@xxxxxxxxxx>
> > Signed-off-by: Zqiang <qiang.zhang@xxxxxxxxx>
> >
> >
> > >
> > > Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > >
> > > 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
> >
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