diff options
| -rw-r--r-- | Documentation/memory-barriers.txt | 17 | ||||
| -rw-r--r-- | include/asm-generic/atomic-long.h | 3 | ||||
| -rw-r--r-- | include/linux/atomic.h | 18 |
3 files changed, 29 insertions, 9 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index 2ba8461b0631..41ffd7e9cdcf 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -637,7 +637,8 @@ as follows: b = p; /* BUG: Compiler and CPU can both reorder!!! */ Finally, the READ_ONCE_CTRL() includes an smp_read_barrier_depends() -that DEC Alpha needs in order to respect control depedencies. +that DEC Alpha needs in order to respect control depedencies. Alternatively +use one of atomic{,64}_read_ctrl(). So don't leave out the READ_ONCE_CTRL(). @@ -796,9 +797,9 @@ site: https://www.cl.cam.ac.uk/~pes20/ppcmem/index.html. In summary: - (*) Control dependencies must be headed by READ_ONCE_CTRL(). - Or, as a much less preferable alternative, interpose - smp_read_barrier_depends() between a READ_ONCE() and the + (*) Control dependencies must be headed by READ_ONCE_CTRL(), + atomic{,64}_read_ctrl(). Or, as a much less preferable alternative, + interpose smp_read_barrier_depends() between a READ_ONCE() and the control-dependent write. (*) Control dependencies can order prior loads against later stores. @@ -820,10 +821,10 @@ In summary: and WRITE_ONCE() can help to preserve the needed conditional. (*) Control dependencies require that the compiler avoid reordering the - dependency into nonexistence. Careful use of READ_ONCE_CTRL() - or smp_read_barrier_depends() can help to preserve your control - dependency. Please see the Compiler Barrier section for more - information. + dependency into nonexistence. Careful use of READ_ONCE_CTRL(), + atomic{,64}_read_ctrl() or smp_read_barrier_depends() can help to + preserve your control dependency. Please see the Compiler Barrier + section for more information. (*) Control dependencies pair normally with other types of barriers. diff --git a/include/asm-generic/atomic-long.h b/include/asm-generic/atomic-long.h index c7a5c1ad2ed3..8942cdc676a7 100644 --- a/include/asm-generic/atomic-long.h +++ b/include/asm-generic/atomic-long.h @@ -35,7 +35,7 @@ typedef atomic_t atomic_long_t; #endif #define ATOMIC_LONG_READ_OP(mo) \ -static inline long atomic_long_read##mo(atomic_long_t *l) \ +static inline long atomic_long_read##mo(const atomic_long_t *l) \ { \ ATOMIC_LONG_PFX(_t) *v = (ATOMIC_LONG_PFX(_t) *)l; \ \ @@ -43,6 +43,7 @@ static inline long atomic_long_read##mo(atomic_long_t *l) \ } ATOMIC_LONG_READ_OP() ATOMIC_LONG_READ_OP(_acquire) +ATOMIC_LONG_READ_OP(_ctrl) #undef ATOMIC_LONG_READ_OP diff --git a/include/linux/atomic.h b/include/linux/atomic.h index 29dafa184aeb..e326469bb9d6 100644 --- a/include/linux/atomic.h +++ b/include/linux/atomic.h @@ -4,6 +4,15 @@ #include <asm/atomic.h> #include <asm/barrier.h> +#ifndef atomic_read_ctrl +static inline int atomic_read_ctrl(const atomic_t *v) +{ + int val = atomic_read(v); + smp_read_barrier_depends(); /* Enforce control dependency. */ + return val; +} +#endif + /* * Relaxed variants of xchg, cmpxchg and some atomic operations. * @@ -455,6 +464,15 @@ static inline int atomic_dec_if_positive(atomic_t *v) #include <asm-generic/atomic64.h> #endif +#ifndef atomic64_read_ctrl +static inline long long atomic64_read_ctrl(const atomic64_t *v) +{ + long long val = atomic64_read(v); + smp_read_barrier_depends(); /* Enforce control dependency. */ + return val; +} +#endif + #ifndef atomic64_andnot static inline void atomic64_andnot(long long i, atomic64_t *v) { |