linux-kernel - Re: [PATCH V3] kmsg_dump: Don't run on non-error paths by default

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Date:	Tue, 14 Feb 2012 13:05:22 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Matthew Garrett <mjg@...hat.com>
Cc:	linux-kernel@...r.kernel.org, dzickus@...hat.com,
	vgoyal@...hat.com, seiji.aguchi@....com
Subject: Re: [PATCH V3] kmsg_dump: Don't run on non-error paths by default

On Fri, 10 Feb 2012 10:45:15 -0500
Matthew Garrett <mjg@...hat.com> wrote:

> Since 04c6862c055fb687c90d9652f32c11a063df15cf kmsg_dump() gets run on
> normal paths including poweroff and reboot. This is less than ideal given
> pstore implementations that can only represent single backtraces, since a
> reboot may overwrite a stored oops before it's been picked up by userspace.
> In addition, some pstore backends may have low performance and provide a
> significant delay in reboot as a result.
> 
> This patch adds a printk.always_kmsg_dump kernel parameter (which can also
> be changed from userspace). Without it, the code will only be run on
> failure paths rather than on normal paths. The option can be enabled in
> environments where there's a desire to attempt to audit whether or not
> a reboot was cleanly requested or not.

So if I'm understanding it correctly, this patch reverts the kernel
behaviour to what it was before 04c6862c055fb687c9 ("kmsg_dump: add
kmsg_dump() calls to the reboot, halt, poweroff and emergency_restart
paths").  The user must now set printk.always_kmsg_dump to get the
04c6862c055fb687c9 behaviour.

Correct?  If so, we should get this into 3.3 so we don't have a oddball
behaviour in one particular kernel release.

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