diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2015-02-20 15:46:31 -0800 |
|---|---|---|
| committer | Sasha Levin <sasha.levin@oracle.com> | 2015-06-28 13:39:28 -0400 |
| commit | d24b9b8d95f0df8c3b1430ff76396fd705cc0140 (patch) | |
| tree | 487908ca48047e6744914e62c1ce19855871fb9b | |
| parent | ac54513c498163cb043c2564d8062596a788f4a2 (diff) | |
kernel: make READ_ONCE() valid on const arguments
[ Upstream commit dd36929720f40f17685e841ae0d4c581c165ea60 ]
The use of READ_ONCE() causes lots of warnings witht he pending paravirt
spinlock fixes, because those ends up having passing a member to a
'const' structure to READ_ONCE().
There should certainly be nothing wrong with using READ_ONCE() with a
const source, but the helper function __read_once_size() would cause
warnings because it would drop the 'const' qualifier, but also because
the destination would be marked 'const' too due to the use of 'typeof'.
Use a union of types in READ_ONCE() to avoid this issue.
Also make sure to use parenthesis around the macro arguments to avoid
possible operator precedence issues.
Tested-by: Ingo Molnar <mingo@kernel.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
| -rw-r--r-- | include/linux/compiler.h | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 33063f872ee3..000c5f90f08c 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -198,7 +198,7 @@ static __always_inline void data_access_exceeds_word_size(void) { } -static __always_inline void __read_once_size(volatile void *p, void *res, int size) +static __always_inline void __read_once_size(const volatile void *p, void *res, int size) { switch (size) { case 1: *(__u8 *)res = *(volatile __u8 *)p; break; @@ -255,10 +255,10 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s */ #define READ_ONCE(x) \ - ({ typeof(x) __val; __read_once_size(&x, &__val, sizeof(__val)); __val; }) + ({ union { typeof(x) __val; char __c[1]; } __u; __read_once_size(&(x), __u.__c, sizeof(x)); __u.__val; }) #define WRITE_ONCE(x, val) \ - ({ typeof(x) __val; __val = val; __write_once_size(&x, &__val, sizeof(__val)); __val; }) + ({ typeof(x) __val = (val); __write_once_size(&(x), &__val, sizeof(__val)); __val; }) #endif /* __KERNEL__ */ |