Date: Thu, 01 Mar 2001 20:44:05 -0800 (PST) From: John Baldwin <jhb@FreeBSD.org> To: Jake Burkholder <jburkholder0829@home.com> Cc: current@FreeBSD.org, Kris Kennaway <kris@obsecurity.org> Subject: Re: Scheduler panic Message-ID: <XFMail.010301204405.jhb@FreeBSD.org> In-Reply-To: <20010302023548.4F733BACC@cr66388-a.rchrd1.on.wave.home.com>
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On 02-Mar-01 Jake Burkholder wrote:
>> > On Sun, Feb 25, 2001 at 10:29:42PM -0800, Kris Kennaway wrote:
>> > > This is on a UP system.
>> >
>> > Had another one of these, under the same conditions. Both times I was
>> > running more(1) on a stdin stream which was generated by a "find |
>> > grep | more" operation, and I suspended the process with ^Z,
>> > triggering the panic. Perhaps this will help in tracking down the
>> > root cause.
>>
>> I'm pretty sure I know what this is; I'll work up a patch tonight.
>>
>
> Sorry this is taking so long. Its turned out to be a little more
> complex to fix properly than I originally thought. We're going to
> have to change the way one of the fields of struct proc (p_pptr)
> is locked. The problem is that a process is getting preempted
> when its not SRUN, which should be protected by the scheduler
> lock so that the preemption can't occur.
>
> This is the best workaround I can think of:
>
> Index: kern/kern_intr.c
> ===================================================================
> RCS file: /home/ncvs/src/sys/kern/kern_intr.c,v
> retrieving revision 1.47
> diff -u -r1.47 kern_intr.c
> --- kern/kern_intr.c 2001/02/28 02:53:43 1.47
> +++ kern/kern_intr.c 2001/03/02 02:28:08
> @@ -366,7 +366,7 @@
> */
> ithread->it_need = 1;
> mtx_lock_spin(&sched_lock);
> - if (p->p_stat == SWAIT) {
> + if (p->p_stat == SWAIT && curproc->p_stat == SRUN) {
> CTR1(KTR_INTR, __func__ ": setrunqueue %d", p->p_pid);
> p->p_stat = SRUN;
> setrunqueue(p);
>
> Jake
Eek, this is wrong. We need to always put it on the runqueue, the trick
is we just need to avoid the actual task switch. This is what I have here:
@@ -369,7 +374,7 @@
CTR1(KTR_INTR, __func__ ": setrunqueue %d", p->p_pid);
p->p_stat = SRUN;
setrunqueue(p);
- if (do_switch) {
+ if (do_switch && curproc->p_stat == SRUN) {
saveintr = sched_lock.mtx_saveintr;
mtx_intr_enable(&sched_lock);
if (curproc != PCPU_GET(idleproc))
(Among other fixes.) I'll try and get this committed tonight if no one screams
bloody murder.
--
John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/
PGP Key: http://www.baldwin.cx/~john/pgpkey.asc
"Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
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