Date: Mon, 23 Jul 2007 10:50:50 -0400 From: John Baldwin <jhb@freebsd.org> To: Andrew Thompson <thompsa@freebsd.org> Cc: cvs-src@freebsd.org, src-committers@freebsd.org, cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/compat/ndis subr_ntoskrnl.c Message-ID: <200707231050.51004.jhb@freebsd.org> In-Reply-To: <200707222053.l6MKrS6v040649@repoman.freebsd.org> References: <200707222053.l6MKrS6v040649@repoman.freebsd.org>
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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. If you try to do this:
foo_detach()
{
mtx_lock(&lock);
please_die = 1;
while (!dead_yet)
msleep(&proc, &lock, ... , hz/10);
mtx_unlock(&lock);
}
foo_main()
{
mtx_lock(&lock);
while (!please_die) {
do_stuff();
}
dead_yet = 1;
mtx_unlock(&lock);
kthread_exit(0);
}
and foo_main() can be unloaded (it's part of a module) then you are still
racey and can panic on kldunload if you foo_main() is preempted after the
mtx_unlock() but before the kthread_exit() and foo_detach() completes and
returns to kldunload() which unmaps the module. I think you didn't make the
race worse though, as the old code was missing the lock and only used
tsleep() before.
--
John Baldwin
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