linux-kernel - Re: [PATCH 0/4] coredump: core dump masking support v3

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Date:	Mon, 26 Feb 2007 11:49:14 +0000
From:	David Howells <dhowells@...hat.com>
To:	Markus Gutschke <markus@...gle.com>
Cc:	"Kawai, Hidehiro" <hidehiro.kawai.ez@...achi.com>,
	Andrew Morton <akpm@...l.org>,
	kernel list <linux-kernel@...r.kernel.org>,
	Pavel Machek <pavel@....cz>, Robin Holt <holt@....com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	sugita <yumiko.sugita.yf@...achi.com>,
	Satoshi OSHIMA <soshima@...hat.com>
Subject: Re: [PATCH 0/4] coredump: core dump masking support v3 

Markus Gutschke <markus@...gle.com> wrote:

> > How does it work when you can't actually get back to userspace to have
> > userspace do the coredump?  You still have to handle the userspace
> > equivalents of double/triple faults.
> 
> My experience shows that there are only very rare occurrences of situations
> where you cannot get back into userspace to do the coredump, and the
> coredumper tries very hard never to cause additional faults.

So what?  If they can occur, you have to handle them.

> While I am sure you could construct scenarios where this would happen,
> realistically the only one I have run into were stack overflows, and they can
> be handled by carefully setting up an alternate stack for signal handlers --
> just make sure the entire stack is already dirtied before you run out of
> memory (or, turn of overcommitting).

Duff SIGSEGV or SIGBUS signal handlers are just as realistic.  All that takes
is for someone to make a programming error.  Remember: error paths are the
least frequently tested.

And any time you say "by carefully setting up" you can guarantee someone's
going to do it wrong.

David
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