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
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