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Date: Thu, 07 Aug 2003 10:23:00 -0400 (EDT)
From: John Baldwin <jhb@FreeBSD.org>
To: Ted Unangst <tedu@stanford.edu>
cc: freebsd-hackers@freebsd.org
Subject: RE: possible deadlocks?
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On 06-Aug-2003 Ted Unangst wrote:
> My advisor Dawson Engler has written a deadlock detector, and we'd like
> some verification. They look like bugs, unless there is some other reason
> why two call chains cannot happen at the same time.
> 
> deadlock between ktrace_mtx and sema_mtx.  is it possible to call
> sema_timewait on ktrace_sema?  call chain below.
> 
> thread 1:
> _sema_timedwait(sema, ...)
>   mtx_lock(&sema->sema_mtx) /* gets this lock */
>     cv_timewait()
>       ktrcsw()
>         ktr_getrequest()
>           mtx_lock(&ktrace_mtx) /* waits for thread 2 */
> 
> thread 2:
> ktr_submitrequest
>   mtx_lock(&ktrace_mtx) /* gets this lock */
>     _sema_post(&ktrace_sema)
>       mtx_lock(&sema->sema_mtx) /* waits for thread 1 */

Yes, the lock isn't needed around the post anyways.  Fixed.

-- 

John Baldwin <jhb@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/