From 19012b786ecccb29a9fa20c4ec0a67e2cdfbc010 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 1 Sep 2020 16:58:41 -0700 Subject: 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: Davidlohr Bueso Signed-off-by: Paul E. McKenney --- kernel/torture.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) (limited to 'kernel/torture.c') diff --git a/kernel/torture.c b/kernel/torture.c index 1061492f14bd..be09377af6bc 100644 --- a/kernel/torture.c +++ b/kernel/torture.c @@ -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)); } -- cgit v1.2.3