Date: Mon, 04 Oct 2004 11:57:45 -0700 From: Julian Elischer <julian@elischer.org> To: Peter Holm <peter@holm.cc> Cc: Stephan Uphoff <ups@tree.com> Subject: Re: scheduler (sched_4bsd) questions Message-ID: <41619D29.1000704@elischer.org> In-Reply-To: <20041004184939.GA8178@peter.osted.lan> References: <1095468747.31297.241.camel@palm.tree.com> <1096496057.3733.2163.camel@palm.tree.com> <1096603981.21577.195.camel@palm.tree.com> <200410041131.35387.jhb@FreeBSD.org> <1096911278.44307.17.camel@palm.tree.com> <20041004184939.GA8178@peter.osted.lan>
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can you run ktrdump against teh corefile and get the ktr output?
(you do have it enabled right?)
Peter Holm wrote:
>On Mon, Oct 04, 2004 at 01:34:38PM -0400, Stephan Uphoff wrote:
>
>
>>On Mon, 2004-10-04 at 11:31, John Baldwin wrote:
>>
>>
>>>On Friday 01 October 2004 12:13 am, Stephan Uphoff wrote:
>>>
>>>
>>>>On Wed, 2004-09-29 at 18:14, Stephan Uphoff wrote:
>>>>
>>>>
>>>>>I was looking at the MUTEX_WAKE_ALL undefined case when I used the
>>>>>critical section for turnstile_claim().
>>>>>However there are bigger problems with MUTEX_WAKE_ALL undefined
>>>>>so you are right - the critical section for turnstile_claim is pretty
>>>>>useless.
>>>>>
>>>>>
>>>>Arghhh !!!
>>>>
>>>>MUTEX_WAKE_ALL is NOT an option in GENERIC.
>>>>I recall verifying that it is defined twice. Guess I must have looked at
>>>>the wrong source tree :-(
>>>>This means yes - we have bigger problems!
>>>>
>>>>Example:
>>>>
>>>>Thread A holds a mutex x contested by Thread B and C and has priority
>>>>pri(A).
>>>>
>>>>Thread C holds a mutex y and pri(B) < pri(C)
>>>>
>>>>Thread A releases the lock wakes thread B but lets C on the turnstile
>>>>wait queue.
>>>>
>>>>An interrupt thread I tries to lock mutex y owned by C.
>>>>
>>>>However priority inheritance does not work since B needs to run first to
>>>>take ownership of the lock.
>>>>
>>>>I is blocked :-(
>>>>
>>>>
>>>Ermm, if the interrupt happens after x is released then I's priority should
>>>propagate from I to C to B.
>>>
>>>
>>There is a hole after the mutex x is released by A - but before B can
>>claim the mutex. The turnstile for mutex x is unowned and interrupt
>>thread I when trying to donate its priority will run into:
>>
>> if (td == NULL) {
>> /*
>> * This really isn't quite right. Really
>> * ought to bump priority of thread that
>> * next acquires the lock.
>> */
>> return;
>> }
>>
>>So B needs to run and acquire the mutex before priority inheritance
>>works again and does not get a priority boost to do so.
>>
>>This is easy to fix and MUTEX_WAKE_ALL can be removed again at that time
>>- but my time budget is limited and Peter has an interesting bug left
>>that has priority.
>>
>>
>
>I'm not closer to being able to create this panic in a controlled way.
>After a whole day of different tests I finally got this panic:
>http://www.holm.cc/stress/log/cons81.html. The trigger seems to be one
>particular Java applet, but it is not easily reproduceable.
>
>- Peter
>
>
>
>>>If the interrupt happens before x is released,
>>>then the final bit of propagate_priority() should handle it since it resorts
>>>the turnstile's thread queue so that C will be awakened rather than B.
>>>
>>>
>>Agreed.
>>
>> Stephan
>>
>>
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