Date: Wed, 21 Mar 2001 11:55:10 +1100 From: Peter Jeremy <peter.jeremy@alcatel.com.au> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: freebsd-alpha@FreeBSD.ORG, jhb@FreeBSD.ORG Subject: Re: user process faulting on kernel address Message-ID: <20010321115509.R26138@gsmx07.alcatel.com.au> In-Reply-To: <15026.37378.477855.889651@grasshopper.cs.duke.edu>; from gallatin@cs.duke.edu on Fri, Mar 16, 2001 at 05:21:54PM -0500 References: <15026.37378.477855.889651@grasshopper.cs.duke.edu>
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On 2001-Mar-16 17:21:54 -0500, Andrew Gallatin <gallatin@cs.duke.edu> wrote: >Note that it is an instruction fault (a2 == -1) and the faulting >address maps to the bottom of witness_exit: > >(kgdb) l *0xfffffc0000418be0 >0xfffffc0000418be0 is in witness_exit (../../kern/kern_mutex.c:1262). ... >The $ra looks reasonable, it is at least a userspace stack address. > >I think somebody saw this a while ago, but I cannot find their >message.. I've got very similar symptoms from ppp. Try looking for a thread 'ppp core-dumping in kernel space?' I first noticed it on 19 Feb <20010219074428.E70642@gsmx07.alcatel.com.au> and posted a followup on 11 Mar <20010311133939.A26976@gsmx07.alcatel.com.au>. My guess is that there is a window between when the user registers are restored and the actual return to usermode during which t12 (at least) can get clobbered. I've occasionally seen odd behaviour in other processes which seems consistent with this behaviour. I haven't looked into it further (I'm not really sure where to start looking). Peter To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-alpha" in the body of the message
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