On Tue, May 19, 2020 at 5:26 PM Marco Elver <el...@google.com> wrote: > > On Tue, 19 May 2020 at 23:10, Qian Cai <c...@lca.pw> wrote: > > > > On Tue, May 12, 2020 at 3:09 PM Peter Zijlstra <pet...@infradead.org> wrote: > > > > > > On Tue, May 12, 2020 at 08:38:39PM +0200, Marco Elver wrote: > > > > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > > > > index 741c93c62ecf..e902ca5de811 100644 > > > > --- a/include/linux/compiler.h > > > > +++ b/include/linux/compiler.h > > > > @@ -224,13 +224,16 @@ void ftrace_likely_update(struct > > > > ftrace_likely_data *f, int val, > > > > * atomicity or dependency ordering guarantees. Note that this may > > > > result > > > > * in tears! > > > > */ > > > > -#define __READ_ONCE(x) (*(const volatile > > > > __unqual_scalar_typeof(x) *)&(x)) > > > > +#define __READ_ONCE(x) > > > > \ > > > > +({ \ > > > > + kcsan_check_atomic_read(&(x), sizeof(x)); \ > > > > + data_race((*(const volatile __unqual_scalar_typeof(x) *)&(x))); \ > > > > +}) > > > > > > NAK > > > > > > This will actively insert instrumentation into __READ_ONCE() and I need > > > it to not have any. > > > > Any way to move this forward? Due to linux-next commit 6bcc8f459fe7 > > (locking/atomics: Flip fallbacks and instrumentation), it triggers a > > lots of KCSAN warnings due to atomic ops are no longer marked. > > This is no longer the right solution we believe due to the various > requirements that Peter also mentioned. See the discussion here: > > https://lkml.kernel.org/r/canpmjnogfqhtda9wwpxs2kztqssozbwsumo5bqqw0c0g0zg...@mail.gmail.com > > The new solution is here: > https://lkml.kernel.org/r/20200515150338.190344-1-el...@google.com > While it's a little inconvenient that we'll require Clang 11 > (currently available by building yourself from LLVM repo), but until > we get GCC fixed (my patch there still pending :-/), this is probably > the right solution going forward. If possible, please do test!
That would be quite unfortunate. The version here is still gcc-8.3.1 and clang-9.0.1 on RHEL 8.2 here. It will probably need many years to be able to get the fixed compilers having versions that high. Sigh... Also, I want to avoid compiling compilers on my own.