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author | Peter Zijlstra <peterz@infradead.org> | 2015-09-18 13:22:52 +0200 |
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committer | Ingo Molnar <mingo@kernel.org> | 2015-09-23 09:54:29 +0200 |
commit | e3e72ab80a3fac0b88e07d358a2c75724ccd66b4 (patch) | |
tree | 3cc1b2f6fbe8ca8d3649d95d14f7c093cea11480 | |
parent | 62e8a3258bda118f24ff462fe04cfbe75b8189b5 (diff) | |
download | linux-stable-e3e72ab80a3fac0b88e07d358a2c75724ccd66b4.tar.gz linux-stable-e3e72ab80a3fac0b88e07d358a2c75724ccd66b4.tar.bz2 linux-stable-e3e72ab80a3fac0b88e07d358a2c75724ccd66b4.zip |
atomic: Implement atomic_read_ctrl()
Provide atomic_read_ctrl() to mirror READ_ONCE_CTRL(), such that we can
more conveniently use atomics in control dependencies.
Since we can assume atomic_read() implies a READ_ONCE(), we must only
emit an extra smp_read_barrier_depends() in order to upgrade to
READ_ONCE_CTRL() semantics.
Requested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Cc: oleg@redhat.com
Link: http://lkml.kernel.org/r/20150918115637.GM3604@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
-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) { |