From: Zqiang <qiang.zhang@linux.dev>
To: paulmck@kernel.org, frederic@kernel.org,
neeraj.upadhyay@kernel.org, joelagnelf@nvidia.com,
urezki@gmail.com, boqun@kernel.org
Cc: qiang.zhang@linux.dev, rcu@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2] rcutorture: Avoid create fwd_prog_tasks for tasks-rude and srcu-atomic
Date: Fri, 23 Oct 2026 17:37:16 +0800 [thread overview]
Message-ID: <20261023093716.25717-1-qiang.zhang@linux.dev> (raw)
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
reply other threads:[~2026-10-23 9:37 UTC|newest]
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