On Tue, Nov 04, 2014 at 09:12:03PM +0100, Pavel Machek wrote: > Hi! > > > Commit-ID: 36df04bc5273a046f53b5e359febc1225f85aa7b > > Gitweb: > > http://git.kernel.org/tip/36df04bc5273a046f53b5e359febc1225f85aa7b > > Author: Peter Zijlstra <pet...@infradead.org> > > AuthorDate: Wed, 29 Oct 2014 12:21:57 +0100 > > Committer: Ingo Molnar <mi...@kernel.org> > > CommitDate: Tue, 4 Nov 2014 07:17:45 +0100 > > > > sched/wait: Reimplement wait_event_freezable() > > > > Provide better implementations of wait_event_freezable() APIs. > > > > The problem is with freezer_do_not_count(), it hides the thread from > > the freezer, even though this thread might not actually freeze/sleep > > at all. > > Can you elaborate? > > The thread will be in freezer_do_not_count() area, but it is just > waiting for event there, it should not do much damage.
There are wait_event()s for which the cond expands to quite a lot of code. This code can still be running while the freezer reports success. This can happen because we're hidden by the do_not_count logic. Also, I initially overlooked that freezer_count() did a try_to_freeze(). > If this is bugfix, should it be cc-ed to stable? Its not a bugfix per se, the issue above is rare and extremely hard to hit, esp since the freezer tries multiple times before giving up. But its a theoretical possibility. > Did you test it with suspend/hibernation? Because I can't really see > how it works. It calls try_to_freeze() after each schedule(). But no, I've not actually tried. If we're stuck in the schedule, waiting for the event, freeze_task() will wake us up and then we'll find freeing() true and call into __refrigerator(). If we're not stuck in schedule() we're running and the freezer can see us running and will wait for us to hit another freeze point. > > +#define __wait_event_freezable(wq, condition) > > \ > > + ___wait_event(wq, condition, TASK_INTERRUPTIBLE, 0, 0, \ > > + schedule(); try_to_freeze()) > > + > _Three_ underscores. And two underscore version exists, too, > fortunately it at least has different number of arguments. Hehe, yeah, there was a discount on underscores that day. The double underscore variants can be used in code along with the no underscores variants. The tripple one is implementation goo. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
