linux-kernel - Re: [PATCH 0/2] add new notifier function ,take3

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Date:	Mon, 14 Apr 2008 10:42:28 -0400
From:	Neil Horman <nhorman@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, nickpiggin@...oo.com.au,
	k-miyoshi@...jp.nec.com, greg@...ah.com,
	Bernhard Walle <bwalle@...e.de>, kdb@....sgi.com,
	kexec@...ts.infradead.org,
	Takenori Nagano <t-nagano@...jp.nec.com>,
	linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...otime.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Keith Owens <kaos@....com.au>
Subject: Re: [PATCH 0/2] add new notifier function ,take3

On Mon, Apr 14, 2008 at 09:46:22AM -0400, Vivek Goyal wrote:
> On Fri, Apr 11, 2008 at 09:07:51PM -0700, Andrew Morton wrote:
> 
> [..]
> > > Kernel panic - not syncing: Panic by panic_module.
> > > __tunable_atomic_notifier_call_chain enter
> > > msg_handler:panic_event was called.
> > > ipmi_wdog:wdog_panic_handler was called.
> > > notifier_test: notifier_test_panic() is called.
> > > notifier_test: notifier_test_panic2() is called.
> > 
> > OK.  But I don't see anywhere in here the most important piece of
> > information: why do we need this feature in Linux?
> > 
> > What are the use-cases?  What is the value?  etc.
> > 
> > Often I can guess (but I like the originator to remove the guesswork).  In
> > this case I'm stumped - I can't see any reason why anyone would want this.
> > 
> 
> Hi Andrew,
> 
> To begin with, he wants kdb, kgdb etc to co-exist with kdump. He wants
> to put all the RAS tools (who are interested in panic event) on a list
> and export it to user space and let user decide in what order do the tool get
> executed at panic time (based on priority).
> 
> This brings in little bit reliability concerns for kdump due to notifier
> code being run after panic.
> 
> I think people want to use this infrastrutucure beyond RAS tools. I
> remember somebody wanting to send a message to remote node after a
> panic (before kdump kicks in)  so that remote node can initiate failover
> etc.
> 
I know it doesn't particularly relate to this patch, but FWIW, for cases like
failover, I've inserted infrastrucutre in the userspace part of kdump for
Fedora/RHEL to support this sort of thing.  We can run arbitrary scripts righte
before and after a capture so that notifications can be sent to remote nodes in
a much safer fashion than using the notifier chain after a panic.
Neil


-- 
/***************************************************
 *Neil Horman
 *Software Engineer
 *Red Hat, Inc.
 *nhorman@...hat.com
 *gpg keyid: 1024D / 0x92A74FA1
 *http://pgp.mit.edu
 ***************************************************/
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