Hi! Alan thinks that `subj` is correct... > > > > At the very least, you'd need rmb() before reading it and wmb() after > > > > writing to it, but I'm not sure if that's enough on every obscure > > > > architecture out there. > > > > > > No, neither one is needed because of the way suspending_task is used. > > > > > > It's not necessary for a reader R to see the variable's actual value; > > > all R needs to know is whether or not suspending_task is equal to R. > > > Since the only process which can set suspending_task to R is R itself, > > > and since R will set suspending_task back to NULL before releasing the > > > write lock on pm_sleep_rwsem, there's never any ambiguity. > > > > Subtle. > > > > Very subtly wrong ;-). > > > > imagine suspending_task == 0xabcdef01. Now task "R" with current == > > 0xabcd0000 reads suspending_task while the other cpu is writing to it, > > and sees 0xabcd0000 (0xef01 was not yet written) -- and mistakenly > > believes that "R" == suspending_task. > > I always thought that reads and writes of pointers are atomic, just > like reads and writes of longs. Is that wrong? ...but I'm not that sure. Can someone clarify? I guess it only works as long as longs are aligned? Should it be written down to atomic_ops.txt? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
