Date: Thu, 16 Sep 2004 13:16:43 -0400 From: John Baldwin <jhb@FreeBSD.org> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: freebsd-threads@FreeBSD.org Subject: Re: Unkillable KSE threaded proc Message-ID: <200409161316.43010.jhb@FreeBSD.org> In-Reply-To: <16713.38977.864343.415015@grasshopper.cs.duke.edu> References: <16703.11479.679335.588170@grasshopper.cs.duke.edu> <414942B3.1060703@elischer.org> <16713.38977.864343.415015@grasshopper.cs.duke.edu>
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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.
--
John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve" = http://www.FreeBSD.org
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