On Thursday, April 14, 2011, Mike Frysinger wrote: > On Wed, Apr 13, 2011 at 18:49, Rafael J. Wysocki wrote: > > On Thursday, April 14, 2011, Mike Frysinger wrote: > >> i guess the trouble for us is that you have one CPU posting writes to > >> task->flags (and doing so by grabbing the task's spinlock), but the > >> other CPU is simply reading those flags. there are no SMP barriers in > >> between the read and write steps, nor is the reading CPU grabbing any > >> locks which would be an implicit SMP barrier. since the Blackfin SMP > >> port lacks hardware cache coherency, there is no way for us to know > >> "we've got to sync the caches before we can do this read". by using > >> the patch i posted above, we have that signal and so things work > >> correctly., > > > > In theory I wouldn't expect the patch to work correctly, because it replaces > > _stronger_ memory barriers with _weaker_ SMP barriers. However, looking at > > the blackfin's definitions of SMP barriers I see that it uses extra stuff that > > should _also_ be used in the definitions of the mandatory barriers. > > > > In my opinion is an architecture problem, not the freezer code problem. > > OK, we have a patch pending locally which populates all barriers with > this logic, but based on my understanding of things, that didnt seem > correct. i guess i'm reading too much into the names ... i'd expect > the opposite behavior where "rmb" is only for UP needs while "smp_rmb" > is a rmb which additionally covers SMP. Well, I guess the naming is for historical reasons, ie. mb(), rmb() and wmb() were there first and it probably was regarded cleaner to use new names for the optimized smp_ variants than to rename all instances already in the code and then repurpose the old names. Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
