Date: Tue, 05 Feb 2002 00:01:35 -0500 (EST) From: John Baldwin <jhb@FreeBSD.org> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Alfred Perlstein <bright@mu.org>, Terry Lambert <tlambert2@mindspring.com>, smp@FreeBSD.org Subject: Re: help with mutex_pool please? Message-ID: <XFMail.020205000135.jhb@FreeBSD.org> In-Reply-To: <200202050432.g154WJ005060@apollo.backplane.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On 05-Feb-02 Matthew Dillon wrote:
>: if (this_is_last_ref_and_I_need_to_die) {
>: mtx_destory(&mumbo_struct->mb_mtx);
>: free(mumbo_struct, M_MUMBO);
>: } else
>: mtx_unlock(...);
>:
>:The optimization is that you avoid the unlock. It might be best to actually
>:keep these semantics and have mtx_destroy() panic if the mutex is marked
>:contested (not a very good way of testing this, but getting sched_lock and
>:hten
>:reading the MTX_CONTESTED bit would catch most cases I would hope) and then
>:set
>:mtx_lock to some invalid value that mtx_lock_sleep() can panic on. All this
>:would only be for the INVARIANTS case of course, and only if the mutex is
>:locked. If you don't allow this, then it's possible for some other code to
>:grab the mutex while you are destroying it which would lead to worse bugs I
>:think. At least we can detect the error condition if we keep the existing
>:semantics.
>:
>:> -Matt
>:> Matthew Dillon
>:> <dillon@backplane.com>
>:
>:--
>:
>:John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
>:"Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
>
> I think it would just be better to fix the cases that assume an unlock
> on destroy and then KASSERT() that the lock is not being held on destroy
> (i.e. panic). Having the API do an auto-unlock-on-destroy is a bad idea.
I agree, but it makes for an easier debug case I think. :-)
> Do you know of any other subsystems that depend on this behavior?
Can't think of any off the top of my head.
> -Matt
> Matthew Dillon
> <dillon@backplane.com>
--
John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-smp" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?XFMail.020205000135.jhb>