Re: [lkp-robot] [torture] b151f93a71: INFO:rcu_preempt_detected_stalls_on_CPUs/tasks

Paul E. McKenney
2017-11-28T21:08:16Z

On Tue, Nov 28, 2017 at 12:46:19PM -0800, Paul E. McKenney wrote:
> On Tue, Nov 28, 2017 at 09:35:54AM -0800, Paul E. McKenney wrote:
> > On Tue, Nov 28, 2017 at 06:10:08PM +0100, Thomas Gleixner wrote:
> > > On Tue, 28 Nov 2017, Paul E. McKenney wrote:
> > > > On Tue, Nov 28, 2017 at 05:47:35PM +0100, Thomas Gleixner wrote:
> > > > diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> > > > index db774b0f217e..a3321bb565db 100644
> > > > --- a/kernel/time/timer.c
> > > > +++ b/kernel/time/timer.c
> > > > @@ -1803,7 +1803,7 @@ signed long __sched schedule_timeout(signed long timeout)
> > > > idx = timer_get_idx(&timer.timer);
> > > > idx_now = calc_wheel_index(j, base->clk);
> > > > raw_spin_unlock_irqrestore(&base->lock, flags);
> > > > - pr_info("%s: Waylayed timer idx: %u idx_now: %u\n", __func__, idx, idx_now);
> > > > + pr_info("%s: Waylayed timer base->clk: %#lx jiffies: %#lx base->next_expiry: %#lx timer->flags: %#x timer->expires %#lx idx: %u idx_now: %u\n", __func__, base->clk, j, base->next_expiry, timer.timer.flags, timer.timer.expires, idx, idx_now);
> > >
> > > Please print idx and idx_now as hex values. It's simpler to decode that way.
> >
> > Here you go! Starting tests at this end, focusing on TREE01 and TREE04.
> > BTW, TREE04 doesn't do any CPU hotplug, providing a counterexample to
> > my long-held assumption that this only happened in the presence of CPU
> > hotplug operations.
>
> And here is output with changes discussed on IRC. TREE04 managed to
> have not one but two overlapping RCU CPU stall warnings, one for RCU-bh
> and the second for RCU-sched. TREE04 and TREE04. HZ=1000.

And here is the full patch, in all its lack of aesthetic appeal.

Thanx, Paul

------------------------------------------------------------------------

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index ffebcf878fba..fbfdc572ceaa 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1755,8 +1755,13 @@ static void process_timeout(struct timer_list *t)
*/
signed long __sched schedule_timeout(signed long timeout)
{
+ struct timer_base *base;
struct process_timer timer;
unsigned long expire;
+ unsigned long flags;
+ unsigned long i;
+ unsigned int idx, idx_now;
+ unsigned long j;

switch (timeout)
{
@@ -1793,6 +1798,17 @@ signed long __sched schedule_timeout(signed long timeout)
timer_setup_on_stack(&timer.timer, process_timeout, 0);
__mod_timer(&timer.timer, expire, 0);
schedule();
+ j = jiffies;
+ if (timeout < 5 && time_after(j, expire + 8 * HZ) && timer_pending(&timer.timer)) {
+ base = lock_timer_base(&timer.timer, &flags);
+ idx = timer_get_idx(&timer.timer);
+ idx_now = calc_wheel_index(j, base->clk);
+ raw_spin_unlock_irqrestore(&base->lock, flags);
+ pr_info("%s: Waylayed timer base->clk: %#lx jiffies: %#lx base->next_expiry: %#lx timer->flags: %#x timer->expires %#lx idx: %x idx_now: %x base->pending_map ", __func__, base->clk, j, base->next_expiry, timer.timer.flags, timer.timer.expires, idx, idx_now);
+ for (i = 0; i < WHEEL_SIZE / sizeof(base->pending_map[0]) / 8; i++)
+ pr_cont("%16lx", base->pending_map[i]);
+ pr_cont("\n");
+ }
del_singleshot_timer_sync(&timer.timer);

/* Remove the timer from the object tracker */