Date: Thu, 16 Sep 2004 21:40:45 -0700 From: Julian Elischer <julian@elischer.org> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-threads@freebsd.org Subject: Re: Unkillable KSE threaded proc Message-ID: <414A6ACD.2020600@elischer.org> In-Reply-To: <200409161316.43010.jhb@FreeBSD.org> References: <16703.11479.679335.588170@grasshopper.cs.duke.edu> <414942B3.1060703@elischer.org> <16713.38977.864343.415015@grasshopper.cs.duke.edu> <200409161316.43010.jhb@FreeBSD.org>
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John Baldwin wrote:
> On Thursday 16 September 2004 09:42 am, Andrew Gallatin wrote:
>
>>Julian Elischer writes:
>> > Andrew, please try -current on ts own now..
>> > I have checked in some fixes that have helped others.
>>
>>OK, preemption off... Still a system lockup, but a little different.
>>
>>The interesting thing here is that continuing and breaking into the
>>debugger repeatedly seems to show that thread 0xc1646af0 is looping in
>>exit. I've seen him in thread_single, thread_suspend_check, and in
>>exit itself at kern_exit.c:163, etc. A breakpoint in
>>thread_suspend_one never triggers, so I guess he's holding the proc
>>lock and just looping forever. A breakpoint in _mtx_assert() shows
>>him asserting the proc lock in thread_suspend_check at kern_thread.c:898.
>>Over and over.
>
>
> There is definitely some sort of infinite loop here. Stripping out the
> comments in exit1() for that section of code reveals basically:
>
> PROC_LOCK(p);
> if (p->p_flag & P_HADTHREADS) {
> retry:
> thread_suspend_check(0);
> if (thread_single(SINGLE_EXIT))
> goto retry;
> }
> p->p_flag |= P_WEXIT;
> PROC_UNLOCK(p);
>
> So it's easy to see how it can stuck in a loop I think. If thread_single()
> never drops the lock then other threads that are waiting to die can't
> actually wait because they can never get the proc lock so that they can die.
>
hmm intersting..
but this code hasn't changed in ages...
in thread_single we see:
thread_suspend_one(td);
PROC_UNLOCK(p);
mi_switch(SW_VOL, NULL);
mtx_unlock_spin(&sched_lock);
PROC_LOCK(p);
mtx_lock_spin(&sched_lock);
so when it sleeps it releases the proc lock.
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