From owner-freebsd-current  Thu Feb 22  7:32:44 2001
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Date: Thu, 22 Feb 2001 17:28:55 +0200
From: Maxim Sobolev <sobomax@FreeBSD.org>
Organization: Vega International Capital
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To: John Baldwin <jhb@FreeBSD.org>
Cc: "Alexander N. Kabaev" <ak03@gte.com>, current@FreeBSD.org,
	Dag-Erling Smorgrav <des@ofug.org>
Subject: Re: A possible bug in the interrupt thread preemption code [Was:
References: <XFMail.010222061816.jhb@FreeBSD.org>
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John Baldwin wrote:

> On 22-Feb-01 Maxim Sobolev wrote:
>
> >> > Here it is (from DDB):
> >> > panic(c027de93,c0297409,c027f878,368,80286)
> >> > _mtx_assert(c02ea000,9,c027f878,368,80286)
> >> > mi_switch(c32c5da0,3,c02cea44,c357be98)
> >> > ithread_schedule(c0747c00,1)
> >> > sched_ithd(e)
> >> > Xresume14()
> >> > --- interrupt, eip = 0xc025b60f, esp = 0x80296, ebp = 0xc357bf08 ---
> >> > trap(18, 10, 10,c01597b6,20)
> >> > calltrap()
> >> > --- trap 0x9, eip = 0xc025a5de, esp = 0xc357bf50, ebp = 0xc357bf64 ---
> >> > sw1b(c0146cbc,c0146cbc,c32c5da0,c357bf94)
> >> > ithread_loop(c0747c00,c357bfa8)
> >> > fork_exit(c0146cbc,c0747c00,c357bfa8)
> >> > fork_trampoline()
> >>
> >> *sigh*  This is why enabling interrupts in trap() is such a bad idea.  If we
> >> get a trap in the scheduler, then lots of bad crap starts to happen because
> >> we
> >> can get an interrupt while we are in a trap. :( Can you compile your kernel
> >> with
> >> INVARIANTS on though, as I think the kernel should've panic'd earlier if it
> >> is
> >> doing what I think it is doing.
> >
> > It's already have INVARIANTS, MUTEX_DEBUG, WITNESS and WITNESS_DDB.
>
> Hmm, ouch, you do'nt want MUTEX_DEBUG, that'll slow your system to a crawl.

It doesn't really matter, because system can't even boot into single-user due to
panic.

> >>  Also, if you are feeling industrious, edit
> >> sys/i386/i386/trap.c and comment out the enable_intr() call near the
> >> beginning
> >> of the trap() function right after the printf for 'kernel trap %d with
> >> interrupts disabled'.
> >
> > Ok, I'll try so.
> >
> > -Maxim
>
> It will still panic, just hopefully a better panic.

I did understand that, but the panic I see after the change is exactly the same as
before. Any other ideas?

-Maxim


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