Messages in this thread | | | Subject | Re: [PATCH] mm: fix a data race in put_page() | From | John Hubbard <> | Date | Sat, 8 Feb 2020 23:12:48 -0800 |
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On 2/8/20 7:10 PM, Qian Cai wrote: > > >> On Feb 8, 2020, at 8:44 PM, John Hubbard <jhubbard@nvidia.com> wrote: >> >> So it looks like we're probably stuck with having to annotate the code. Given >> that, there is a balance between how many macros, and how much commenting. For >> example, if there is a single macro (data_race, for example), then we'll need to >> add comments for the various cases, explaining which data_race situation is >> happening. > > On the other hand, it is perfect fine of not commenting on each data_race() that most of times, people could run git blame to learn more details. Actually, no maintainers from various of subsystems asked for commenting so far. >
Well, maybe I'm looking at this wrong. I was thinking that one should attempt to understand the code on the screen, and that's generally best--but here, maybe "data_race" is just something that means "tool cruft", really. So mentally we would move toward visually filtering out the data_race "key word".
I really don't like it but at least there is a significant benefit from the tool that probably makes it worth the visual noise.
Blue sky thoughts for The Far Future: It would be nice if the tools got a lot better--maybe in the direction of C language extensions, even if only used in this project at first.
thanks, -- John Hubbard NVIDIA
>> >> That's still true, but to a lesser extent if more macros are added. In this case, >> I suspect that READ_BITS() makes the commenting easier and shorter. So I'd tentatively >> lead towards adding it, but what do others on the list think? > > Even read bits could be dangerous from data races and confusing at best, so I am not really sure what the value of introducing this new macro. People who like to understand it correctly still need to read the commit logs. > > This flags->zonenum is such a special case that I don’t really see it regularly for the last few weeks digging KCSAN reports, so even if it is worth adding READ_BITS(), there are more equally important macros need to be added together to be useful initially. For example, HARMLESS_COUNTERS(), READ_SINGLE_BIT(), READ_IMMUTATABLE_BITS() etc which Linus said exactly wanted to avoid. >
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