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Date: Wed, 4 May 2005 12:41:04 -0700
From: Andrew Morton <akpm@osdl.org>
To: Alexander Nyberg <alexn@dsv.su.se>
Cc: andre@cachola.com.br, cw@f00f.org, linux-kernel@vger.kernel.org
Subject: Re: A patch for the file kernel/fork.c
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Alexander Nyberg <alexn@dsv.su.se> wrote:
>
> > [4300748.423000] Call Trace:
> > [4300748.423000]  [<c0104bfa>] show_stack+0x7a/0x90
> > [4300748.423000]  [<c0104d7d>] show_registers+0x14d/0x1b0
> > [4300748.423000]  [<c0104fcc>] die+0x14c/0x2c0
> > [4300748.423000]  [<c0118b6f>] do_page_fault+0x31f/0x638
> > [4300748.423000]  [<c01046df>] error_code+0x4f/0x54
> > [4300748.423000]  [<c02b88fd>] tty_wakeup+0x5d/0x60
> > 
> > I think that maybe it's good to put a:
> >        WARN_ON(!mm);
> > but a BUG_ON or without this patch, the kernel will halt, even if the 
> > problem is not so severe.
> 
> Patching up the kernel hiding things that must not happen is not the way
> to go. All kernel bugs are severe (as you just showed us!). Adding extra
> checks like your original patch did may even cause much more harm
> because it may hide other problems causing silent problems.

If I understand Andre correctly, his patch will prevent infinite recursion
in the oops path - if some process oopses after having run exit_mm().

If so then it's a reasonable debugging aid.  Although there might be better
places to do it, such as

	if (!current->i_tried_to_exit++)
		return;

in do_exit().   Dunno.
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