On Sun, 9 Feb 2020 21:41:56 -0500 Qian Cai <cai@xxxxxx> wrote: > > > > On Feb 9, 2020, at 9:20 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > Using data_race() here seems misleading - there is no race, but we're > > using data_race() to suppress a false positive warning from KCSAN, yes? > > It is a data race in the sense of compilers, i.e., KCSAN is a compiler instrumentation, so here the load and store are both in word-size, but code here is only interested in 3 bits which are never changed. Thus, it is a harmless data race. > > Marco also mentioned, > > “Various options were considered, and based on feedback from Linus, > decided 'data_race(..)' is the best option:” > > lore.kernel.org/linux-fsdevel/CAHk-=wg5CkOEF8DTez1Qu0XTEFw_oHhxN98bDnFqbY7HL5AB2g@xxxxxxxxxxxxxx/ > > Paul also said, > > ”People will get used to the name more quickly than they will get used > to typing the extra seven characters. Here is the current comment header: > > /* > * data_race(): macro to document that accesses in an expression may conflict with > * other concurrent accesses resulting in data races, but the resulting > * behaviour is deemed safe regardless. > * > * This macro *does not* affect normal code generation, but is a hint to tooling > * that data races here should be ignored. > */ > > I will be converting this to docbook form. > > In addition, in the KCSAN documentation: > > * KCSAN understands the ``data_race(expr)`` annotation, which tells KCSAN that > any data races due to accesses in ``expr`` should be ignored and resulting > behaviour when encountering a data race is deemed safe.” OK. But I believe page_zonenum() still deserves a comment explaining that there is no race and explaining why we're using data_race() anyway. Otherwise the use of data_race() is simply misleading.
