Re: lockdep splat in CPU hotplug

From: Daniel Lezcano
Date: Wed Oct 22 2014 - 10:45:13 EST


On 10/22/2014 04:36 PM, Jiri Kosina wrote:
On Wed, 22 Oct 2014, Daniel Lezcano wrote:

I am seeing the lockdep report below when resuming from suspend-to-disk
with current Linus' tree (c2661b80609).

The reason for CCing Ingo and Peter is that I can't make any sense of one
of the stacktraces lockdep is providing.

Please have a look at the very first stacktrace in the dump, where lockdep
is trying to explain where cpu_hotplug.lock#2 has been acquired. It seems
to imply that cpuidle_pause() is taking cpu_hotplug.lock, but that's not
the case at all.

What am I missing?

Okay, reverting 442bf3aaf55a ("sched: Let the scheduler see CPU idle
states") and followup 83a0a96a5f26 ("sched/fair: Leverage the idle state
info when choosing the "idlest" cpu") which depends on it makes the splat
go away.

Are you able to reproduce it by offlining the cpu and onlining it again ?

No, that doesn't trigger it (please note that all the relevant stacktraces
from lockdep are going through hibernation).

Ok, thanks.


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