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Commit 0c133dd0 authored by Linus Torvalds's avatar Linus Torvalds
Browse files
Pull WRITE_ONCE argument order change from Christian Borntraeger:
 "As discussed on LKML[1] it was agreed that WRITE_ONCE(x, val) is
  better than ASSIGN_ONCE(val, x)

  Lets change that for 3.19 as 3.19 has no user yet, but the first users
  will hit linux-next soon"

[1] http://marc.info/?l=linux-kernel&m=142081181707596

* tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux:
  kernel: Change ASSIGN_ONCE(val, x) to WRITE_ONCE(x, val)
parents e7a823be 43239cbe
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+6 −6
Original line number Diff line number Diff line
@@ -215,7 +215,7 @@ static __always_inline void __read_once_size(volatile void *p, void *res, int si
	}
}

static __always_inline void __assign_once_size(volatile void *p, void *res, int size)
static __always_inline void __write_once_size(volatile void *p, void *res, int size)
{
	switch (size) {
	case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
@@ -235,15 +235,15 @@ static __always_inline void __assign_once_size(volatile void *p, void *res, int
/*
 * Prevent the compiler from merging or refetching reads or writes. The
 * compiler is also forbidden from reordering successive instances of
 * READ_ONCE, ASSIGN_ONCE and ACCESS_ONCE (see below), but only when the
 * READ_ONCE, WRITE_ONCE and ACCESS_ONCE (see below), 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 READ_ONCE,
 * ASSIGN_ONCE or ACCESS_ONCE() in different C statements.
 * WRITE_ONCE or ACCESS_ONCE() in different C statements.
 *
 * In contrast to ACCESS_ONCE these two macros will also work on aggregate
 * data types like structs or unions. If the size of the accessed data
 * type exceeds the word size of the machine (e.g., 32 bits or 64 bits)
 * READ_ONCE() and ASSIGN_ONCE()  will fall back to memcpy and print a
 * READ_ONCE() and WRITE_ONCE()  will fall back to memcpy and print a
 * compile-time warning.
 *
 * Their two major use cases are: (1) Mediating communication between
@@ -257,8 +257,8 @@ static __always_inline void __assign_once_size(volatile void *p, void *res, int
#define READ_ONCE(x) \
	({ typeof(x) __val; __read_once_size(&x, &__val, sizeof(__val)); __val; })

#define ASSIGN_ONCE(val, x) \
	({ typeof(x) __val; __val = val; __assign_once_size(&x, &__val, sizeof(__val)); __val; })
#define WRITE_ONCE(x, val) \
	({ typeof(x) __val; __val = val; __write_once_size(&x, &__val, sizeof(__val)); __val; })

#endif /* __KERNEL__ */