From: Gerald Schaefer <gerald.schaefer@de.ibm.com>
To: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Hugh Dickins <hughd@google.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Martin Schwidefsky <martin.schwidefsky@de.ibm.com>,
Heiko Carstens <h.carstens@de.ibm.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Chris Wright <chrisw@sous-sol.org>,
Izik Eidus <izik.eidus@ravellosystems.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: ksm/memory hotplug: lockdep warning for ksm_thread_mutex vs. (memory_chain).rwsem
Date: Fri, 03 Feb 2012 16:37:48 +0100 [thread overview]
Message-ID: <4F2BFF4C.5050905@de.ibm.com> (raw)
In-Reply-To: <CAHGf_=rm286b5FWVRQ8Ob0vakxNcNOHPUksCtnZj4PvOEz47Jg@mail.gmail.com>
On 03.02.2012 00:00, KOSAKI Motohiro wrote:
> 2012/2/2 Gerald Schaefer<gerald.schaefer@de.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.
There is no real deadlock and no user visible buggy behaviour, the memory is
being offlined as requested. I think your conclusion from last time is still
valid, that both locks are inside mem_hotplug_mutex and there can't be a
deadlock. Question is how to convince lockdep of this.
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next prev parent reply other threads:[~2012-02-03 15:38 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-02 16:13 ksm/memory hotplug: lockdep warning for ksm_thread_mutex vs. (memory_chain).rwsem Gerald Schaefer
2012-02-02 23:00 ` KOSAKI Motohiro
2012-02-03 15:37 ` Gerald Schaefer [this message]
2012-07-16 12:49 ` Gerald Schaefer
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