Date: Mon, 24 Sep 2001 12:33:32 -0700 (PDT) From: John Baldwin <jhb@FreeBSD.org> To: Wilko Bulte <wkb@freebie.xs4all.nl> Cc: Garrett Wollman <wollman@khavrinen.lcs.mit.edu>, current@FreeBSD.org Subject: Re: Seen this lock order reversal? Message-ID: <XFMail.010924123332.jhb@FreeBSD.org> In-Reply-To: <20010923204929.A11867@freebie.xs4all.nl>
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On 23-Sep-01 Wilko Bulte wrote:
> On Thu, Sep 20, 2001 at 07:40:52PM +0200, Wilko Bulte wrote:
>> On Wed, Sep 19, 2001 at 01:32:28PM -0700, John Baldwin wrote:
>> >
>> > On 19-Sep-01 Wilko Bulte wrote:
>> > > On Tue, Sep 18, 2001 at 03:01:25PM -0700, John Baldwin wrote:
>>
>> ...
>>
>> > >> p_flag to p_sflag which changed its locking semantics.)
>> > >
>> > > Another one, on a -current from yesterday, on -alpha:
>> > >
>> > > lock order reversal
>> > > 1st 0xfffffc00007fcef0 clk @ ../../../alpha/alpha/clock.c:702
>> > > 2nd 0xfffffc00007f65d8 callout @ ../../../kern/kern_timeout.c:225
>> > > ds10#
>> >
>> > Hmm, ok, that one is new and is a problem. Can you turn on WITNESS_DDB
>> > (it's
>> > available as the debug.witness_ddb sysctl and loader variableas well) and
>> > then
>> > get me a traceback in ddb?
>>
>> I built a GENERIC with WITNESS_DDB. Sofar (of course... :-/ ) no
>> reproduction of the problem. I'm running buildworlds, any other good
>> suggestions to help trigger it are welcome
>
> Bah. I cannot reproduce this on my DS10.
>
> Is there any reason to assume that specifying CPUTYPE ev56 has any
> influence on the lock order reversal? By default world is built with
> ev4, but I have gone to ev56 now. Rumor has it that results in 'less
> buggy' code.
No. Hmmm. You didn't have any KTR traces enabled did you?
Hmm, that first one is in sysbeep() (the clk one) Ah!
if (!beeping) {
/* enable counter2 output to speaker */
if (pitch) outb(IO_PPI, inb(IO_PPI) | 3);
beeping = period;
timeout(sysbeepstop, (void *)NULL, period);
}
This is the problem code. Hmmm. The i386 code seems b0rked. It doesn't have
enough locks! Eck. hmm, the pc98 code doesn't even _use_ the mutex but still
depends on disable/enable intr. Eek. I'll work at this later on today.
--
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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