torture: Periodically pause in stutter_wait()
Running locktorture scenario LOCK05 results in hangs:
tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --torture lock --duration 3 --configs LOCK05
The lock_torture_writer() kthreads set themselves to MAX_NICE while
running SCHED_OTHER. Other locktorture kthreads run at default niceness,
also SCHED_OTHER. This results in these other locktorture kthreads
indefinitely preempting the lock_torture_writer() kthreads. Note that
the cond_resched() in the stutter_wait() function's loop is ineffective
because this scenario is built with CONFIG_PREEMPT=y.
It is not clear that such indefinite preemption is supposed to happen, but
in the meantime this commit prevents kthreads running in stutter_wait()
from being completely CPU-bound, thus allowing the other threads to get
some CPU in a timely fashion.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
diff --git a/kernel/torture.c b/kernel/torture.c
index 1061492..9310c1d 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -602,6 +602,7 @@ static int stutter_gap;
*/
bool stutter_wait(const char *title)
{
+ unsigned i = 0;
int spt;
bool ret = false;
@@ -612,8 +613,13 @@ bool stutter_wait(const char *title)
if (spt == 1) {
schedule_timeout_interruptible(1);
} else if (spt == 2) {
- while (READ_ONCE(stutter_pause_test))
+ while (READ_ONCE(stutter_pause_test)) {
+ if (!(++i & 0xffff))
+ schedule_timeout_interruptible(1);
+ else if (!(i & 0xfff))
+ udelay(1);
cond_resched();
+ }
} else {
schedule_timeout_interruptible(round_jiffies_relative(HZ));
}
