Messages in this thread | | | Date | Tue, 9 Apr 2019 03:36:18 +0200 | From | Andrea Parri <> | Subject | Re: Adding plain accesses and detecting data races in the LKMM |
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> > The formula was more along the line of "do not assume either of these > > cases to hold; use barrier() is you need an unconditional barrier..." > > AFAICT, all current implementations of smp_mb__{before,after}_atomic() > > provides a compiler barrier with either barrier() or "memory" clobber. > > Well, we have two reasonable choices: Say that > smp_mb__{before,after}_atomic will always provide a compiler barrier, > or don't say this. I see no point in saying that the combination of > Before-atomic followed by RMW provides a barrier.
;-/ I'm fine with the first choice. I don't see how the second choice (this proposal/patch) would be consistent with some documentation and with the current implementations; for example,
1) Documentation/atomic_t.txt says:
Thus:
atomic_fetch_add();
is equivalent to:
smp_mb__before_atomic(); atomic_fetch_add_relaxed(); smp_mb__after_atomic();
[...]
2) Some implementations of the _relaxed() variants do not provide any compiler barrier currently.
Andrea
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