On Tue, 17 Nov 2020 16:42:44 -0800 Matt Mullins <mmullins@xxxxxxx> wrote: > > Indeed with a stub function, I don't see any need for READ_ONCE/WRITE_ONCE. > > I'm not sure if this is a practical issue, but without WRITE_ONCE, can't > the write be torn? A racing __traceiter_ could potentially see a > half-modified function pointer, which wouldn't work out too well. This has been discussed before, and Linus said: "We add READ_ONCE and WRITE_ONCE annotations when they make sense. Not because of some theoretical "compiler is free to do garbage" arguments. If such garbage happens, we need to fix the compiler" https://lore.kernel.org/lkml/CAHk-=wi_KeD1M-_-_SU_H92vJ-yNkDnAGhAS=RR1yNNGWKW+aA@xxxxxxxxxxxxxx/ > > This was actually my gut instinct before I wrote the __GFP_NOFAIL > instead -- currently that whole array's memory ordering is provided by > RCU and I didn't dive deep enough to evaluate getting too clever with > atomic modifications to it. The pointers are always going to be the architecture word size (by definition), and any compiler that tears a write of a long is broken. -- Steve
