linux-kernel - Re: ksm/memory hotplug: lockdep warning for ksm_thread_mutex vs. (memory

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Date:	Thu, 2 Feb 2012 18:00:45 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	gerald.schaefer@...ibm.com
Cc:	Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Martin Schwidefsky <martin.schwidefsky@...ibm.com>,
	Heiko Carstens <h.carstens@...ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Izik Eidus <izik.eidus@...ellosystems.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: ksm/memory hotplug: lockdep warning for ksm_thread_mutex vs. (memory_chain).rwsem

2012/2/2 Gerald Schaefer <gerald.schaefer@...ibm.com>:
> Setting a memory block offline triggers the following lockdep warning. This
> looks exactly like the issue reported by Kosaki Motohiro in
> https://lkml.org/lkml/2010/10/25/110. 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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