Date: Mon, 23 Jul 2007 12:20:27 -0700 From: Nate Lawson <nate@root.org> To: John Baldwin <jhb@freebsd.org> Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org, Andrew Thompson <thompsa@freebsd.org> Subject: Re: cvs commit: src/sys/compat/ndis subr_ntoskrnl.c Message-ID: <46A4FF7B.5000501@root.org> In-Reply-To: <200707231050.51004.jhb@freebsd.org> References: <200707222053.l6MKrS6v040649@repoman.freebsd.org> <200707231050.51004.jhb@freebsd.org>
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John Baldwin wrote:
> On Sunday 22 July 2007 04:53:28 pm Andrew Thompson wrote:
>> thompsa 2007-07-22 20:53:28 UTC
>>
>> FreeBSD src repository
>>
>> Modified files:
>> sys/compat/ndis subr_ntoskrnl.c
>> Log:
>> ndis will signal the kthread to exit and then sleep on the proc pointer to
>> be woken up by kthread_exit. This is racey and in some cases the kthread
> will
>> exit before ndis gets around to sleep so it will be stuck indefinitely.
> This
>> change reuses the kq_exit variable to indicate that the thread has gone
> and
>> will loop on tsleep with a timeout waiting for it. If the kthread has
> already
>> exited then it will not sleep at all.
>
> As long as you use a lock you are ok. That is:
>
> foo_detach()
> {
>
> mtx_lock(&lock);
> please_die = 1;
> msleep(&proc, &lock, ..., 0);
> mtx_unlock(&lock);
> }
>
> foo_main()
> {
>
> mtx_lock(&lock);
> while (!please_die) {
> do_stuff();
> }
> mtx_unlock(&lock);
> kthread_exit(0);
> }
>
> works fine.
How can foo_detach() acquire the lock to set "please_die" if foo_main()
always holds it? Are you assuming that "do_stuff()" drops the lock
somewhere internally?
-Nate
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