On 05/10, Paul E. McKenney wrote: > > On Fri, May 10, 2024 at 01:31:49PM +0200, Oleg Nesterov wrote: > > > Why is that? > > Because I run KCSAN on RCU using Kconfig options that cause KCSAN > to be more strict. Yes, I see now. > > but how can KCSAN detect that all accesses to X are properly marked? I see nothing > > KCSAN-related in the definition of WRITE_ONCE() or READ_ONCE(). > > The trick is that KCSAN sees the volatile cast that both READ_ONCE() > and WRITE_ONCE() use. Hmm. grep-grep-grep... I seem to understand, DEFINE_TSAN_VOLATILE_READ_WRITE. So __tsan_volatile_readX() will use KCSAN_ACCESS_ATOMIC. Thanks! > > And what does the "all accesses" above actually mean? The 2nd version does > > > > WRITE_ONCE(X, X+1); > > > > but "X + 1" is the plain/unmarked access? > > ... > > In that case, the "X+1" cannot be involved in a data race, so KCSAN > won't complain. Yes, yes, I understand now. Paul, thanks for your explanations! and sorry for wasting your time by provoking the unnecessarily long discussion. I am going to send the trivial patch which moves these WARN_ON()'s under spin_lock(), this looks more clean to me. But I won't argue if you prefer your original patch. Oleg.
