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Re: Issue with core dump

To: trisha yad <trisha1march@gmail.com>
Subject: Re: Issue with core dump
From: Ralf Baechle <ralf@linux-mips.org>
Date: Wed, 2 Nov 2011 11:30:31 +0000
Cc: Oleg Nesterov <oleg@redhat.com>, linux-mm <linux-mm@kvack.org>, Russell King - ARM Linux <linux@arm.linux.org.uk>, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, kamezawa.hiroyu@jp.fujitsu.com, mhocko@suse.cz, rientjes@google.com, Andrew Morton <akpm@linux-foundation.org>, Konstantin Khlebnikov <khlebnikov@openvz.org>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, "Rafael J. Wysocki" <rjw@sisk.pl>, Rusty Russell <rusty@rustcorp.com.au>, Tejun Heo <htejun@gmail.com>
In-reply-to: <CAGr+u+wgAYVWgdcG6o+6F0mDzuyNzoOxvsFwq0dMsR3JNnZ-cA@mail.gmail.com>
References: <CAGr+u+zkPiZpGefstcbJv_cj929icWKXbqFy1uR22Hns1hzFeQ@mail.gmail.com> <20111101152320.GA30466@redhat.com> <CAGr+u+wgAYVWgdcG6o+6F0mDzuyNzoOxvsFwq0dMsR3JNnZ-cA@mail.gmail.com>
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On Wed, Nov 02, 2011 at 12:03:39PM +0530, trisha yad wrote:

> Thanks all for your answer.
> 
> In loaded embedded system the time at with code hit do_user_fault()
> and core_dump_wait() is bit
> high, I check on my  system it took 2.7 sec. so it is very much
> possible that core dump is not correct.
> It  contain global value updated.
> 
> So is it possible at time of send_signal() we can stop modification of
> faulty thread memory ?

On existing hardware it is impossible to take a consistent snapshot of a
multi-threaded application at the time of one thread faulting.

A software simulator can handle this sort of race condition but of course
this approach has other disadvantages.

  Ralf

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