Date: Tue, 11 Mar 2003 08:43:46 +1100 From: Tim Robbins <tjr@FreeBSD.org> To: John Baldwin <jhb@FreeBSD.org> Cc: Kris Kennaway <kris@obsecurity.org>, alfred@FreeBSD.org, current@FreeBSD.org, Poul-Henning Kamp <phk@phk.freebsd.dk> Subject: Re: NULL pointer problem in pid selection ? Message-ID: <20030311084346.A63542@dilbert.robbins.dropbear.id.au> In-Reply-To: <XFMail.20030310130015.jhb@FreeBSD.org>; from jhb@FreeBSD.org on Mon, Mar 10, 2003 at 01:00:15PM -0500 References: <20030308213535.GE56020@rot13.obsecurity.org> <XFMail.20030310130015.jhb@FreeBSD.org>
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On Mon, Mar 10, 2003 at 01:00:15PM -0500, John Baldwin wrote:
> On 08-Mar-2003 Kris Kennaway wrote:
> > On Sat, Mar 08, 2003 at 11:46:34AM +0100, Poul-Henning Kamp wrote:
> >>
> >> Just got this crash on -current, and I belive I have seen similar
> >> before. addr2line(1) reports the faulting address to be
> >> ../../../kern/kern_fork.c:395
> >> which is in the inner loop of pid collision avoidance.
> >
> > I've been running this patch from Alfred for the past month or so on
> > bento, which has fixed a similar panic I was seeing regularly.
>
> Using just a shared lock instead of an xlock should be ok there. You
> aren't modifying the process tree, just looking at it. OTOH, the
> proc lock is supposed to protect p_grp and p_session, so they shouldn't
> be NULL. :(
I have a suspiscion that the bug is actually in wait1():
sx_xlock(&proctree_lock);
[...]
/*
* Remove other references to this process to ensure
* we have an exclusive reference.
*/
leavepgrp(p);
sx_xlock(&allproc_lock);
LIST_REMOVE(p, p_list); /* off zombproc */
sx_xunlock(&allproc_lock);
LIST_REMOVE(p, p_sibling);
sx_xunlock(&proctree_lock);
Shouldn't we be removing the process from zombproc before setting
p_pgrp to NULL via leavepgrp()? Does this even matter at all when both
fork1() and wait1() are still protected by Giant?
Tim
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