Date: Thu, 05 Oct 2000 14:46:49 -0700 (PDT) From: John Baldwin <jhb@FreeBSD.org> To: John Baldwin <jhb@FreeBSD.org> Cc: freebsd-current@FreeBSD.org, freebsd-smp@FreeBSD.org, Boris Popov <bp@butya.kz> Subject: RE: Problems with kthread_exit() and SMPng Message-ID: <XFMail.001005144649.jhb@FreeBSD.org> In-Reply-To: <XFMail.001005143107.jhb@FreeBSD.org>
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Ugh, my mail client ate my reply, lemme try again.
> On 05-Oct-00 Boris Popov wrote:
>> Hello,
>>
>> Currently I'm trying to make KLD which uses kernel threads
>> unloadable under recent -current. The prototype of functions looks like
>> this:
>>
>> void
>> my_thread(void*arg)
>> {
>> while(wearewanted) {
>> do_something();
>> tsleep();
>> }
>> exited = 1;
>> kthread_exit(0);
>> }
You need Giant before calling kthread_exit().
>> void
>> my_unload()
>> {
>> wearewanted = 0;
>> while (!exited)
>> tsleep(1sec);
>> }
>>
>> my_unload() function called from the module unload event which
>> issued from the kldunload() syscall.
>>
>> Unfortunately, kernel panics in the mtx_exit_hard() function.
>> After some examination I've found that two fields in the Giant mutex
>> structure set to unexpected values:
It should have died much earlier if you had INVARIANTS turned on. :( It
looks like you are releasing a mutex you probably do not own because
cpu_exit() (called by exit1() -> exit() -> kthread_exit()) releases Giant
as one of its final tasks.
>> ----
>> empty mtx_blocked for mutex Giant
>> mtx_contested not in any list for mutex Giant
>> ----
>>
>> These messages printed by added diagnostics code. With this patch
>> (see attachment) it is possible to load and unload KLD without any
>> problems on UP machine except that the above messages printed. However,
>> I'm don't know if they are correct. (btw, 4.1 doesn't have this problem).
This patch is bogus I'm afraid. A contested mutex should always have a
process waiting to grab it when it is released.
--
John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/
PGP Key: http://www.baldwin.cx/~john/pgpkey.asc
"Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
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