On Wed, 2 Apr 2008 10:59:26 -0700, "Rao, Nikhil" <[EMAIL PROTECTED]> wrote:
> Thanks for all your replies,
>
> the all_proc lock is held in pfind(..) at the point PROC_LOCK(p) is
> obtained. In the kern_wait(..) code below, the allproc_lock is acquired
> before removing the proc from the list of all procs. The PROC_LOCK is
> then acquired before continuing. Since the thread that called pfind(..)
> has the PROC_LOCK, kern_wait(..) would need to wait for it to release
> the PROC_LOCK before continuing. I hope this understanding is correct.
>
> In http://fxr.watson.org/fxr/source/kern/kern_exit.c?v=RELENG62#L579
>
> sx_xlock(&allproc_lock);
> 675 LIST_REMOVE(p, p_list); /* off zombproc */
> 676 sx_xunlock(&allproc_lock);
> 677 LIST_REMOVE(p, p_sibling);
> 678 leavepgrp(p);
> 679 sx_xunlock(&proctree_lock);
> 680
> 681 /*
> 682 * As a side effect of this lock, we know
> that
> 683 * all other writes to this proc are visible
> now, so
> 684 * no more locking is needed for p.
> 685 */
> 686 PROC_LOCK(p);
Yes, line 686 above will have to wait for any holders of the proc lock
on the specific proc entry. The allproc_lock is not needed anymore,
because these last lines are inside:
if (p->p_state == PRS_ZOMBIE) {
...
After the zombie process has been removed from the zombie list, we will
have to wait until the proc entry is unlocked. At that point, the proc
entry is no longer on the zombie list, so it won't be locked by anyone
else. We grab the lock, clean it up and it's gone for good.
_______________________________________________
freebsd-hackers@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-hackers
To unsubscribe, send any mail to "[EMAIL PROTECTED]"
