rcutorture: Avoid create fwd_prog_tasks for tasks-rude and srcu-atomic

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 <[email protected]>

Signed-off-by Zqiang <[email protected]>

---
 kernel/rcu/rcutorture.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

kernel/rcu/rcutorture.c +2 -3

index 968343be4e0d..92ff197f4789 100644
@@ -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;

Signature · 1 line

2.17.1

Quoted 33 lines

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.

Quoted 8 lines

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 <[email protected]>

Signed-off-by Zqiang <[email protected]>

Reviewed-by Paul E. McKenney <[email protected]>

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. ;-)

Quoted 25 lines

---
 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