diff options
Diffstat (limited to 'include/linux/compiler.h')
| -rw-r--r-- | include/linux/compiler.h | 33 |
1 files changed, 30 insertions, 3 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 338111a448d0..50bb2461648f 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -198,20 +198,37 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, #include <asm/barrier.h> #include <linux/kasan-checks.h> -#define __READ_ONCE(x) (*(volatile typeof(x) *)&(x)) +/* + * Use __READ_ONCE() instead of READ_ONCE() if you do not require any + * atomicity or dependency ordering guarantees. Note that this may result + * in tears! + */ +#define __READ_ONCE(x) (*(const volatile typeof(x) *)&(x)) -#define READ_ONCE(x) \ +#define __READ_ONCE_SCALAR(x) \ ({ \ typeof(x) __x = __READ_ONCE(x); \ smp_read_barrier_depends(); \ __x; \ }) -#define WRITE_ONCE(x, val) \ +#define READ_ONCE(x) \ +({ \ + compiletime_assert_rwonce_type(x); \ + __READ_ONCE_SCALAR(x); \ +}) + +#define __WRITE_ONCE(x, val) \ do { \ *(volatile typeof(x) *)&(x) = (val); \ } while (0) +#define WRITE_ONCE(x, val) \ +do { \ + compiletime_assert_rwonce_type(x); \ + __WRITE_ONCE(x, val); \ +} while (0) + #ifdef CONFIG_KASAN /* * We can't declare function 'inline' because __no_sanitize_address conflicts @@ -313,6 +330,16 @@ static inline void *offset_to_ptr(const int *off) compiletime_assert(__native_word(t), \ "Need native word sized stores/loads for atomicity.") +/* + * Yes, this permits 64-bit accesses on 32-bit architectures. These will + * actually be atomic in many cases (namely x86), but for others we rely on + * the access being split into 2x32-bit accesses for a 32-bit quantity (e.g. + * a virtual address) and a strong prevailing wind. + */ +#define compiletime_assert_rwonce_type(t) \ + compiletime_assert(__native_word(t) || sizeof(t) == sizeof(long long), \ + "Unsupported access size for {READ,WRITE}_ONCE().") + /* &a[0] degrades to a pointer: a different type from an array */ #define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0])) |