diff options
author | Uros Bizjak <ubizjak@gmail.com> | 2024-04-10 09:29:34 +0300 |
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committer | Ingo Molnar <mingo@kernel.org> | 2024-04-10 16:04:54 +0300 |
commit | e73c4e34a0e9e3dfcb4e5ee4ccd3039a7b603218 (patch) | |
tree | a760c0320424e5387a89e4b42ccaa15c9e0447ad | |
parent | 276b893049e4cdc2f33c009706a75ec18a114485 (diff) | |
download | linux-e73c4e34a0e9e3dfcb4e5ee4ccd3039a7b603218.tar.xz |
locking/atomic/x86: Introduce arch_atomic64_read_nonatomic() to x86_32
Introduce arch_atomic64_read_nonatomic() for 32-bit targets to load
the value from atomic64_t location in a non-atomic way. This
function is intended to be used in cases where a subsequent atomic
operation will handle the torn value, and can be used to prime the
first iteration of unconditional try_cmpxchg() loops.
Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20240410062957.322614-2-ubizjak@gmail.com
-rw-r--r-- | arch/x86/include/asm/atomic64_32.h | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/arch/x86/include/asm/atomic64_32.h b/arch/x86/include/asm/atomic64_32.h index ec217aaf41eb..bbdf174de110 100644 --- a/arch/x86/include/asm/atomic64_32.h +++ b/arch/x86/include/asm/atomic64_32.h @@ -14,6 +14,32 @@ typedef struct { #define ATOMIC64_INIT(val) { (val) } +/* + * Read an atomic64_t non-atomically. + * + * This is intended to be used in cases where a subsequent atomic operation + * will handle the torn value, and can be used to prime the first iteration + * of unconditional try_cmpxchg() loops, e.g.: + * + * s64 val = arch_atomic64_read_nonatomic(v); + * do { } while (!arch_atomic64_try_cmpxchg(v, &val, val OP i); + * + * This is NOT safe to use where the value is not always checked by a + * subsequent atomic operation, such as in conditional try_cmpxchg() loops + * that can break before the atomic operation, e.g.: + * + * s64 val = arch_atomic64_read_nonatomic(v); + * do { + * if (condition(val)) + * break; + * } while (!arch_atomic64_try_cmpxchg(v, &val, val OP i); + */ +static __always_inline s64 arch_atomic64_read_nonatomic(const atomic64_t *v) +{ + /* See comment in arch_atomic_read(). */ + return __READ_ONCE(v->counter); +} + #define __ATOMIC64_DECL(sym) void atomic64_##sym(atomic64_t *, ...) #ifndef ATOMIC64_EXPORT #define ATOMIC64_DECL_ONE __ATOMIC64_DECL |