On Tue, Feb 18, 2020 at 09:26:44PM +0100, Peter Zijlstra wrote: > On Tue, Feb 18, 2020 at 08:34:05AM -0800, Paul E. McKenney wrote: > > On Tue, Feb 18, 2020 at 12:43:34PM +0100, Peter Zijlstra wrote: > > > > Well, I didn't get further than the Changelog fails to describe an > > > actual problem and it looks like compare-against-a-constant. > > > > > > (worse, it masks off everything but the 2 lowest bits, so even if there > > > was a problem with load-tearing, it still wouldn't matter) > > > > There is still the possibility of load fusing. > > Agreed; that can be an issue. But if so, that then needs to be stated. > > > And the possibility > > of defending against possible future changes as well as the current > > snapshot of the code base. > > Sure; and like I said, if you want to use READ_ONCE() I'm not going to > argue. > > > > I'm not going to argue with you if you want to use READ_ONCE() vs > > > data_race() and a comment to denote false-positive KCSAN warnings, but I > > > do feel somewhat strongly that the Changelog should describe the actual > > > problem -- if there is one -- or just flat out state that this is to > > > make KCSAN shut up but the code is fine. > > > > The problem is that "the code is fine" is highly subjective and varies > > over time. :-/ > > > > But in this case there was a real problem, just that I got confused > > when analyzing. > > Shit happens :-) > > > > That is; every KCSAN report should be analysed, right? All I'm asking is > > > for that analysis to end up in the Changelog. > > > > Before responding further, I have to ask... > > > > Are you intending your "every KCSAN report should be analyzed" to apply > > globally or just when someone creates a patch based on such a report? > > Ideally every KCSAN report, but that is a longer term effort. But > specifically, when someone has written a patch, I expect that same > someone to have analysed the code. Then it also makes sense to put that > in the Changelog. > > > In any case, you have acked this patch's successor (thank you very > > much!), so on this specific patch (or more accurately, its successor) > > I presume that we are all good. > > We are. That new patch describes a clear problem and fixes it. > > Anyway, the reaoson I'm being difficuly is partly because on the one > hand I'm just an annoying pendant at times, but also because I've seen > a bunch of, let's say, hasty, KCSAN patches. Agreed. I briefly considered putting KCSAN for RCU on the newbie list, but looking at a few of them put paid to that idea. Responding to them properly does require a reasonably deep understanding of the code. Thanx, Paul
