This is a note to let you know that I've just added the patch titled kernel: make READ_ONCE() valid on const arguments to the 3.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kernel-make-read_once-valid-on-const-arguments.patch and it can be found in the queue-3.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From dd36929720f40f17685e841ae0d4c581c165ea60 Mon Sep 17 00:00:00 2001 From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Date: Fri, 20 Feb 2015 15:46:31 -0800 Subject: kernel: make READ_ONCE() valid on const arguments From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxx> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/linux/compiler.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -198,7 +198,7 @@ static __always_inline void data_access_ { } -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 */ #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__ */ Patches currently in stable-queue which might be from torvalds@xxxxxxxxxxxxxxxxxxxx are queue-3.19/x86-spinlocks-paravirt-fix-memory-corruption-on-unlock.patch queue-3.19/x86-irq-fix-regression-caused-by-commit-b568b8601f05.patch queue-3.19/ntp-fixup-adjtimex-freq-validation-on-32-bit-systems.patch queue-3.19/kernel-make-read_once-valid-on-const-arguments.patch queue-3.19/proc-pagemap-walk-page-tables-under-pte-lock.patch queue-3.19/mm-hugetlb-pmd_huge-returns-true-for-non-present-hugepage.patch queue-3.19/fsnotify-fix-handling-of-renames-in-audit.patch queue-3.19/random-fix-fast_mix-function.patch queue-3.19/x86-mm-aslr-fix-stack-randomization-on-64-bit-systems.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html