Re: ksm/memory hotplug: lockdep warning for ksm_thread_mutex vs. (memory_chain).rwsem

From: KOSAKI Motohiro
Date: Thu Feb 02 2012 - 18:01:05 EST

2012/2/2 Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>:
> Setting a memory block offline triggers the following lockdep warning. This
> looks exactly like the issue reported by Kosaki Motohiro in
> Seems like the resulting commit a0b0f58cdd
> did not fix the lockdep warning. I'm able to reproduce it with current 3.3.0-rc2
> as well as 2.6.37-rc4-00147-ga0b0f58.
> I'm not familiar with lockdep annotations, but I tried using down_read_nested()
> for (memory_chain).rwsem, similar to the mutex_lock_nested() which was
> introduced for ksm_thread_mutex, but that didn't help.

Heh, interesting. Simple question, do you have any user visible buggy
behavior? or just false positive warn issue?

*_nested() is just hacky trick. so, any change may break their lie.
Anyway I'd like to dig this one. thanks for reporting.
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