Date: Fri, 24 Dec 2004 00:03:41 +0100 (MET) From: Jan Engelhardt <jengelh@linux01.gwdg.de> To: Max Laier <max@love2party.net> Cc: freebsd-hackers@freebsd.org Subject: Re: Kernel crash w/o reason Message-ID: <Pine.LNX.4.61.0412232355100.8807@yvahk01.tjqt.qr> In-Reply-To: <200412232307.41735.max@love2party.net> References: <Pine.LNX.4.61.0412232230270.11442@yvahk01.tjqt.qr> <200412232307.41735.max@love2party.net>
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>1) In kmi_fops.d_open():
>| if(!mtx_trylock(&Open_lock)) { return EBUSY; }
>| return 0;
>
>this can not work. You cannot return to userland with a lock acquired.
So? The full code also contains a uio_read() function. If I release the
lock in uio_read(), no crash happens. It's just in uio_close().
Why can't I hold this lock, as it is possible with Linux? A mutex is basically
just an atomic counter AFAIK, and if nobody releases it in-between, it is
still held by the time we enter uio_close() - thus it could be unlocked
without problems. In theory at least.
What should I use instead? A semaphore?
>2) If you report a problem, try to provide an error message. In this case a
>crashdump/panic string. When you do kernel programming you should always run
>in a debug kernel. To debug this specific problem WITNESS is helpful.
I've tracked it a little and found out that it is mtx_unlock() which crashes,
or more precisely, it is line
td1 = turnstile_head(ts)
in _mtx_unlock_sleep() -- ts == NULL! I have dug deep into &m->mtx_object and
it looks like the TC list (in turnstile_lookup) is empty, but I do not know
why.
>4) Why on earth do you use gmake? What's wrong with bsd.*.mk? It's a whole lot
>easier.
Because non-BSD (read: Linux, MINGW/MSYS and Cygwin) do not ship BSD make. And
of course, that I got to GNU make first and had few joy to learn another make
syntax.
Jan Engelhardt
--
ENOSPC
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