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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2015-02-20 15:46:31 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-03-06 14:57:42 -0800 |
| commit | b6888abd998c2ac2d2a3291cc205556762dda581 (patch) | |
| tree | fc71d2e949d6956087b19ded90f6c1cd16e9e630 | |
| parent | fec1418da2939d368d934d787f340dd667edc5b7 (diff) | |
| download | lwn-b6888abd998c2ac2d2a3291cc205556762dda581.tar.gz lwn-b6888abd998c2ac2d2a3291cc205556762dda581.zip | |
kernel: make READ_ONCE() valid on const arguments
commit dd36929720f40f17685e841ae0d4c581c165ea60 upstream.
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -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 0b203111c166..fa6a31441d04 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__ */ |