Move ACCESS_ONCE() to <linux/compiler.h>

It actually makes much more sense there, and we do tend to need it for
non-RCU usage too.  Moving it to <linux/compiler.h> will allow some
other cases that have open-coded the same logic to use the same helper
function that RCU has used.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2008-05-10 19:51:16 -07:00
parent 3ed43c745d
commit 9c3cdc1f83
2 changed files with 12 additions and 12 deletions

View File

@ -182,4 +182,16 @@ extern void __chk_io_ptr(const volatile void __iomem *);
# define __section(S) __attribute__ ((__section__(#S)))
#endif
/*
* Prevent the compiler from merging or refetching accesses. The compiler
* is also forbidden from reordering successive instances of ACCESS_ONCE(),
* but only when the compiler is aware of some particular ordering. One way
* to make the compiler aware of ordering is to put the two invocations of
* ACCESS_ONCE() in different C statements.
*
* This macro does absolutely -nothing- to prevent the CPU from reordering,
* merging, or refetching absolutely anything at any time.
*/
#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
#endif /* __LINUX_COMPILER_H */

View File

@ -131,18 +131,6 @@ struct rcu_head {
*/
#define rcu_read_unlock_bh() __rcu_read_unlock_bh()
/*
* Prevent the compiler from merging or refetching accesses. The compiler
* is also forbidden from reordering successive instances of ACCESS_ONCE(),
* but only when the compiler is aware of some particular ordering. One way
* to make the compiler aware of ordering is to put the two invocations of
* ACCESS_ONCE() in different C statements.
*
* This macro does absolutely -nothing- to prevent the CPU from reordering,
* merging, or refetching absolutely anything at any time.
*/
#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
/**
* rcu_dereference - fetch an RCU-protected pointer in an
* RCU read-side critical section. This pointer may later