On Thu, Dec 12, 2019 at 2:46 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > +#ifdef GCC_VERSION < 40800 Where does that 4.8 version check come from, and why? Yeah, I know, but this really wants a comment. Sadly it looks like gcc bugzilla is down, so https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 currently gives an "Internal Server Error" for me. [ Delete the horrid code we have because of gcc bugs ] > +#else /* GCC_VERSION < 40800 */ > + > +#define READ_ONCE_NOCHECK(x) \ > +({ \ > + typeof(x) __x = *(volatile typeof(x))&(x); \ I think we can/should just do this unconditionally if it helps th eissue. Maybe add a warning about how gcc < 4.8 might mis-compile the kernel - those versions are getting close to being unacceptable for kernel builds anyway. We could also look at being stricter for the normal READ/WRITE_ONCE(), and require that they are (a) regular integer types (b) fit in an atomic word We actually did (b) for a while, until we noticed that we do it on loff_t's etc and relaxed the rules. But maybe we could have a "non-atomic" version of READ/WRITE_ONCE() that is used for the questionable cases? Linus
