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SubjectRe: Query regarding synchronize_sched_expedited and resched_cpu
On Mon, Sep 18, 2017 at 12:29:31PM -0400, Steven Rostedt wrote:
> On Mon, 18 Sep 2017 09:24:12 -0700
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
>
>
> > As soon as I work through the backlog of lockdep complaints that
> > appeared in the last merge window... :-(
> >
> > sparse_irq_lock, I am looking at you!!! ;-)
>
> I just hit one too, and decided to write a patch to show a chain of 3
> when applicable.

Hello Steven,

I really agree with this. Currently, in case that more than two locks
participates in a deadlock, the report informs insuffucuently.

Thanks,
Byungchul

>
> For example:
>
> Chain exists of:
> cpu_hotplug_lock.rw_sem --> smpboot_threads_lock --> (complete)&self->parked
>
> Possible unsafe locking scenario by crosslock:
>
> CPU0 CPU1 CPU2
> ---- ---- ----
> lock(smpboot_threads_lock);
> lock((complete)&self->parked);
> lock(cpu_hotplug_lock.rw_sem);
> lock(smpboot_threads_lock);
> lock(cpu_hotplug_lock.rw_sem);
> unlock((complete)&self->parked);
>
> *** DEADLOCK ***
>
> :-)
>
> -- Steve

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