On Mon, Jun 25, 2007 at 02:43:32PM +0400, Oleg Nesterov wrote:
> Rafael J. Wysocki wrote:
> >
> > static int usermodehelper_pm_callback(struct notifier_block *nfb,
> > unsigned long action,
> > void *ignored)
> > {
> > + long retval;
> > +
> > switch (action) {
> > case PM_HIBERNATION_PREPARE:
> > case PM_SUSPEND_PREPARE:
> > usermodehelper_disabled = 1;
> > - return NOTIFY_OK;
> > + /*
> > + * From now on call_usermodehelper_exec() won't start any new
> > + * helpers, so it is sufficient if running_helpers turns out to
> > + * be zero at one point (it may be increased later, but that
> > + * doesn't matter).
> > + */
> > + retval = wait_event_timeout(running_helpers_waitq,
> > + atomic_read(&running_helpers) == 0,
> > + RUNNING_HELPERS_TIMEOUT);
> > + if (retval) {
> > + return NOTIFY_OK;
> > + } else {
> > + usermodehelper_disabled = 0;
> > + return NOTIFY_BAD;
>
> I think this is racy. First, this needs smp_mb() between
> "usermodehelper_disabled = 1"
> and wait_event_timeout().
>
> Second, call_usermodehelper's path should first increment the counter, and
> only
> then check usermodehelper_disabled, and it needs an mb() in between too.
> Otherwise,
> the helper can see usermodehelper_disabled == 0, then PM_SUSPEND_PREPARE
> comes and
> returns NOTIFY_OK, then the helper increments the counter and starts
> application.
>
> Sadly, you can't use srcu/qrcu because it doesn't handle timeouts.
Interesting... So the thought is to have a synchronize_srcu_timeout()
or something similar that waited for a grace period to elapse or for
a timeout to expire, whichever comes first? It should not be too hard
to arrange something, if needed.
Thanx, Paul
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
