Re: [RC][PATCH -mm] PM: Prevent frozen user mode helpers from failing the freezing of tasks

[Pavel Machek <pavel@ucw.cz>]

Hi!

> > > Special thanks to Uli Luckas <u.luckas@road.de> for reviewing the previous
> > > versions of this patch and for very useful comments.
> > ...
> > > Reviewed-by: Pavel Machek <pavel@ucw.cz>
> > 
> > Eh, not sure this header is worth anything. Sometimes I'm lazy and
> > stop when I see first problem.
> > 
> > >  	switch (action) {
> > >  	case PM_HIBERNATION_PREPARE:
> > >  	case PM_SUSPEND_PREPARE:
> > >  		usermodehelper_disabled = 1;
> > > -		return NOTIFY_OK;
> > > +		retval = wait_event_timeout(running_helpers_waitq,
> > > +					atomic_read(&running_helpers) == 0,
> > 
> > Are you sure here? What happens when atomic variable changes between
> > the atomic_read and the function call?
> 
> Er, this is a macro. :-)
> 
> In fact we rely only on atomic_read(&running_helpers) being still zero after
> helper_finished() has woken us up, but I think that's acceptable.
> 
> IOW, if the wait_event_timeout() returns with retval different from zero, this
> means that atomic_read(&running_helpers) returned zero at one point after
> we'd set usermodehelper_disabled, which is enough.  OTOH, if it doesn't

Ok, can you write short comment explaining that? /* We have set
usermodehelper_disabled, so any new usermode helpers are not a problem
*/.

									Pavel
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