<<On Thu, 05 Apr 2001 14:41:29 -0700 (PDT), John Baldwin <[EMAIL PROTECTED]> said:
> As a safety check we should probably zero the pid right before zfree()'ing a
> proc in wait() however, so that a stale pointer to a free'd process doesn't
> have a valid pid if we do this.
Should not be necessary. Here is the logic:
p = sip->si_p;
mtx_lock_spin(&sched_lock);
if (p->p_stat != SZOMB || p->p_pid != sip->si_pid) {
/* oops */
mtx_lock_spin(&sched_lock);
return;
}
sip->si_pid = 0;
sip->si_p = 0;
if (p->p_wchan == (caddr_t)&selwait) {
/* ... */
If `p' is a pointer to a freed process, then p->p_stat is guaranteed
to be SZOMB -- the only code path which can free a process struct is
wrapped inside `if (p->p_stat == SZOMB)'. (See kern_exit.c:exit1().)
If `p' is a pointer to an active process, and it's the wrong pid, then
we don't wake it up. Otherwise, we wake it up. (`p' might still be
the wrong process, if pid space wrapped around, but the current code
doesn't deal with that condition, either, nor should it.)
-GAWollman
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