Date: Mon, 10 Mar 2003 17:46:40 -0500 (EST) From: John Baldwin <jhb@FreeBSD.org> To: Tim Robbins <tjr@FreeBSD.org> Cc: Poul-Henning Kamp <phk@phk.freebsd.dk>, current@FreeBSD.org, alfred@FreeBSD.org, Kris Kennaway <kris@obsecurity.org> Subject: Re: NULL pointer problem in pid selection ? Message-ID: <XFMail.20030310174640.jhb@FreeBSD.org> In-Reply-To: <20030311084346.A63542@dilbert.robbins.dropbear.id.au>
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On 10-Mar-2003 Tim Robbins wrote: > 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? Giant doesn't help you with sleeps. However, removing the process from zombproc before destroying it's other linkages might be more correct, yes. > Tim -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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