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locking: Remove atomicy checks from {READ,WRITE}_ONCE

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The fact that volatile allows for atomic load/stores is a special case
not a requirement for {READ,WRITE}_ONCE(). Their primary purpose is to
force the compiler to emit load/stores _once_.

Change-Id: I713b57e95c81b5d49a04e5562f13ad46a7b2341d
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Git-commit: 7bd3e239d6c6d1cad276e8f130b386df4234dcd7
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Signed-off-by: Trilok Soni <tsoni@codeaurora.org>
This commit is contained in:
Peter Zijlstra 2015-03-26 17:45:37 +01:00 committed by followmsi
parent 85346f5b6b
commit eac509b8f8
1 changed files with 1 additions and 13 deletions
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14
include/linux/compiler.h
View file

@ -170,17 +170,7 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
#include <linux/types.h>
static __always_inline void data_access_exceeds_word_size(void)
#ifdef __compiletime_warning
__compiletime_warning("data access exceeds word size and won't be atomic")
#endif
;
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;
@ -189,7 +179,6 @@ static __always_inline void __read_once_size(volatile void *p, void *res, int si
default:
barrier();
__builtin_memcpy((void *)res, (const void *)p, size);
data_access_exceeds_word_size();
barrier();
}
}
@ -203,7 +192,6 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
default:
barrier();
__builtin_memcpy((void *)p, (const void *)res, size);
data_access_exceeds_word_size();
barrier();
}
}