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| author | kib <kib@FreeBSD.org> | 2015-06-29 09:58:40 +0000 |
|---|---|---|
| committer | kib <kib@FreeBSD.org> | 2015-06-29 09:58:40 +0000 |
| commit | f6cfae6dab50dc678aaac4311af58a17c322cf97 (patch) | |
| tree | 84c4fa88f9644193bcb94c03b48ab4d8554cae1d /sys/amd64/include/atomic.h | |
| parent | e85612a06dab6982c547776bf09273b97d2f995f (diff) | |
| download | FreeBSD-src-f6cfae6dab50dc678aaac4311af58a17c322cf97.zip FreeBSD-src-f6cfae6dab50dc678aaac4311af58a17c322cf97.tar.gz | |
Add a comment about too strong semantic of atomic_load_acq() on x86.
Submitted by: bde
MFC after: 2 weeks
Diffstat (limited to 'sys/amd64/include/atomic.h')
| -rw-r--r-- | sys/amd64/include/atomic.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/sys/amd64/include/atomic.h b/sys/amd64/include/atomic.h index dceb3dc..6d5c6b6 100644 --- a/sys/amd64/include/atomic.h +++ b/sys/amd64/include/atomic.h @@ -296,6 +296,15 @@ __storeload_barrier(void) } #endif /* _KERNEL*/ +/* + * C11-standard acq/rel semantics only apply when the variable in the + * call is the same for acq as it is for rel. However, our previous + * (x86) implementations provided much stronger ordering than required + * (essentially what is called seq_cst order in C11). This + * implementation provides the historical strong ordering since some + * callers depend on it. + */ + #define ATOMIC_LOAD(TYPE) \ static __inline u_##TYPE \ atomic_load_acq_##TYPE(volatile u_##TYPE *p) \ |
