ACCESS_ONCE does not work reliably on non-scalar types. For example gcc 4.6 and 4.7 might remove the volatile tag for such accesses during the SRA (scalar replacement of aggregates) step https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145) Let's provide READ_ONCE/ASSIGN_ONCE that will do all accesses via scalar types. Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> --- include/linux/compiler.h | 34 ++++++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) diff --git a/include/linux/compiler.h b/include/linux/compiler.h index d5ad7b1..0ff01f2 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -186,6 +186,40 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); # define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__) #endif +#include <linux/types.h> + +static __always_inline void __assign_once_size(volatile void *p, void *res, int size) +{ + switch (size) { + case 1: *(volatile u8 *)p = *(u8 *)res; break; + case 2: *(volatile u16 *)p = *(u16 *)res; break; + case 4: *(volatile u32 *)p = *(u32 *)res; break; +#ifdef CONFIG_64BIT + case 8: *(volatile u64 *)p = *(u64 *)res; break; +#endif + } +} + +#define ASSIGN_ONCE(val, p) \ + ({ typeof(p) __val; __val = val; __assign_once_size(&p, &__val, sizeof(__val)); __val; }) + + +static __always_inline void __read_once_size(volatile void *p, void *res, int size) +{ + switch (size) { + case 1: *(u8 *)res = *(volatile u8 *)p; break; + case 2: *(u16 *)res = *(volatile u16 *)p; break; + case 4: *(u32 *)res = *(volatile u32 *)p; break; +#ifdef CONFIG_64BIT + case 8: *(u64 *)res = *(volatile u64 *)p; break; +#endif + } +} + +#define READ_ONCE(p) \ + ({ typeof(p) __val; __read_once_size(&p, &__val, sizeof(__val)); __val; }) + + #endif /* __KERNEL__ */ #endif /* __ASSEMBLY__ */ -- 1.9.3
