linux-kernel - Re: [PATCH] exec: Make do_coredump more robust and safer when using pipes in core

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Date:	Sat, 01 Aug 2009 19:28:52 +0100
From:	Scott James Remnant <scott@...ntu.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	earl_chew@...lent.com
Subject: Re: [PATCH] exec: Make do_coredump more robust and safer when
 using pipes in core_pattern

On Sat, 2009-08-01 at 09:41 -0400, Neil Horman wrote:

> > > Not without additional work.  If init crashed in the initramfs, I don't think
> > > theres a way to handle that.  If it crashes at some later time, I think it just
> > > gets restarted IIRC.  I'm sure you can change that behavior, but this patch
> > > doesn't address that.
> > > 
> > When the system init daemon crashes, the kernel PANICs.  When not using
> > core_pattern, this is ok, we get a core file - when using apport, as far
> > as I can tell it never waits for apport to finish so we don't get the
> > crash.
> > 
> This is non-sensical.  If init crashes, and the kernel panics, you'll only get a
> core by sheer luck and good fortune.
> 
Or by being a bit clever.  Upstart catches the SIGSEGV and the signal
handler forks a child process, unmasking the signal in that child
process with no signal handler installed.

So it's really a child of init that core dumps, just ignore the signal
handler off the top of the stack trace and it's just as good as a core
dump from the init daemon itself.

Meanwhile the real init daemon (pid 1) wait()s on its child, and then
once it's reaped it exits itself - and then the kernel PANICs.


This works just fine with ordinary core files, because the kernel does
at least write out the core file beforehand.  With apport we don't get
this wait, thus I was hoping your patch would have that effect.

Scott
-- 
Scott James Remnant
scott@...ntu.com

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