Re: [PATCH 1/9] PM: Add suspend block api.

Alan Stern
2010-04-23T16:45:41Z

On Fri, 23 Apr 2010, Alan Stern wrote:

> On Thu, 22 Apr 2010, [UTF-8] Arve HjÃ¸nnevÃ¥g wrote:

> > +struct suspend_blocker {
> > +#ifdef CONFIG_SUSPEND_BLOCKERS
> > + atomic_t flags;
> > + const char *name;
> > +#endif
>
> Why is flags an atomic_t? Are you worried that drivers might try to
> activate a suspend_blocker at the same time that it is being destroyed?
> If this happens, does the code do the right thing? I don't think it
> does -- if a race occurs, suspend_block() will leave flags set to the
> wrong value. The same goes for suspend_unblock().
>
> Since these routines don't nest, there is also the possibility of a
> race between suspend_block() and suspend_unblock(). If the race goes
> one way the blocker is active; the other way it isn't. Given that such
> problems already exist, why worry about what happens when the suspend
> blocker is destroyed?

Having now read the later patches, I see that you switch over to using
a spinlock instead of an atomic_t. My suggestion is to use a spinlock
right from the start. It will be less confusing.

Alan Stern