On Fri, Jul 22, 2016 at 01:53:13AM +0200, Rafael J. Wysocki wrote: > On Fri, Jul 22, 2016 at 1:45 AM, Steve Muckle <[email protected]> wrote: > > On Fri, Jul 22, 2016 at 01:32:00AM +0200, Rafael J. Wysocki wrote: > >> On Fri, Jul 22, 2016 at 1:22 AM, Steve Muckle <[email protected]> > >> wrote: > >> > On Fri, Jul 22, 2016 at 01:22:22AM +0200, Rafael J. Wysocki wrote: > >> >> OK, applied. > >> > > >> > FWIW I do have a concern on this patch, I think it adds unnecessary > >> > overhead. > >> > >> It isn't unnecessary. It prevents an otherwise possible kernel crash > >> from happening. > > > > The logic may not be unecessary, but the overhead is. The crash could be > > prevented in a way that doesn't require repeatedly checking a pointer > > that doesn't change. > > Well, you had the ->resolve_freq check in your patch, didn't you? > > Viresh simply added a ->target_index check to it. > > Now, you can argue that this is one check too many, but as long as > drivers are allowed to implement ->target without implementing > ->resolve_freq, the *number* of checks in this routine cannot be > reduced. > > There are three possible cases and two checks are required to > determine which case really takes place.
My thinking was that one of these two would be preferable: - Forcing ->target() drivers to install a ->resolve_freq callback, enforcing this at cpufreq driver init time. My understanding is ->target() drivers are deprecated anyway and theren't aren't many of them, though I don't know offhand exactly how many or how hard it would be to do for each one. - Forcing callers (schedutil in this case) to check that either ->target() or ->resolve_freq() is implemented. It means catching and scrutinizing future callers of resolve_freq. But even if one of these is better than it could always be done on top of this patch I suppose. I'm also not familiar with the platforms that use ->target() style drivers. So strictly speaking for my purposes it won't matter since the number of tests is the same for them.
