Re: frequent lockups in 3.18rc4
From: Ingo Molnar
Date: Fri Nov 21 2014 - 01:37:54 EST
* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> That's *especially* true if it turns out that the 3.17 problem
> you saw was actually a perf bug that has already been fixed and
> is in stable. We've been looking at kernel/smp.c changes, and
> looking for x86 IPI or APIC changes, and found some harmlessly
> (at least on x86) suspicious code and this exercise might be
> worth it for that reason, but what if it's really just a
> scheduler regression.
> There's been a *lot* more scheduler changes since 3.17 than the
> small things we've looked at for x86 entry or IPI handling. And
> the scheduler changes have been about things like overloaded
> scheduling groups etc, and I could easily imaging that some bug
> *there* ends up causing the watchdog process not to schedule.
> Hmm? Scheduler people?
Hm, that's a possibility, yes.
The watchdog threads are pretty simple beasts though, using
kernel/watchdog.c: watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
which is typically only affected by less than 10% of scheduler
changes - but it's entirely possible still.
It might make sense to disable the softlockup detector altogether
and just see whether trinity finishes/wedges, whether a login
over the console is still possible - etc.
The softlockup messages in themselves are only analytical, unless
CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE=1 is used.
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