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SubjectRe: Query regarding synchronize_sched_expedited and resched_cpu
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.

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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