Commit 19012b78 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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.  This commit also uses hrtimers to provide
very short sleeps to avoid degrading the sudden-on testing that stutter
is supposed to provide.

Reviewed-by: default avatarDavidlohr Bueso <dbueso@suse.de>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 3480d677

kernel/torture.c

+14 −2
Original line number Diff line number Diff line
@@ -602,8 +602,11 @@ static int stutter_gap; 
 */

bool stutter_wait(const char *title)

{

	int spt;

	ktime_t delay;

	unsigned int i = 0;

	int oldnice;

	bool ret = false;

	int spt;



	cond_resched_tasks_rcu_qs();

	spt = READ_ONCE(stutter_pause_test);
@@ -612,8 +615,17 @@ bool stutter_wait(const char *title) 
		if (spt == 1) {

			schedule_timeout_interruptible(1);

		} else if (spt == 2) {

			while (READ_ONCE(stutter_pause_test))

			oldnice = task_nice(current);

			set_user_nice(current, MAX_NICE);

			while (READ_ONCE(stutter_pause_test)) {

				if (!(i++ & 0xffff)) {

					set_current_state(TASK_INTERRUPTIBLE);

					delay = 10 * NSEC_PER_USEC;

					schedule_hrtimeout(&delay, HRTIMER_MODE_REL);

				}

				cond_resched();

			}

			set_user_nice(current, oldnice);

		} else {

			schedule_timeout_interruptible(round_jiffies_relative(HZ));

		}