linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <20141118220254.GA2571@redhat.com>
Date:	Tue, 18 Nov 2014 17:02:54 -0500
From:	Dave Jones <davej@...hat.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: frequent lockups in 3.18rc4

On Tue, Nov 18, 2014 at 04:55:40PM -0500, Don Zickus wrote:

 > > So here we mangle CPU3 in and lose the backtrace for cpu0, which might
 > > be the real interesting one ....
 > 
 > Can you provide another dump?  The hope is we get something not mangled?

Working on it..

 > The other option we have done in RHEL is panic the system and let kdump
 > capture the memory.  Then we can analyze the vmcore for the stack trace
 > cpu0 stored in memory to get a rough idea where it might be if the cpu
 > isn't responding very well.

I don't know if it's because of the debug options I typically run with,
or that I'm perpetually cursed, but I've never managed to get kdump to
do anything useful. (The last time I tried it was actively harmful in
that not only did it fail to dump anything, it wedged the machine so
it didn't reboot after panic).

Unless there's some magic step missing from the documentation at
http://fedoraproject.org/wiki/How_to_use_kdump_to_debug_kernel_crashes
then I'm not optimistic it'll be useful.

	Dave

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