iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

As discussed on LKML http://marc.info/?l=linux-kernel&m=142081181707596

Browse Source 
it was agreement 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.
 -----BEGIN PGP SIGNATURE-----
 Version: GnuPG v2.0.14 (GNU/Linux)
 
 iQIcBAABAgAGBQJUtXl3AAoJEBF7vIC1phx8QLsQAIthwLT9FC94YWYrKYkC1CT3
 CY8gvjVXIki+CVs/a1qdcvuKXj4qLHBDO2ignhPvbqesmHyqIa010gsIT7sm6/d4
 GyDY5AIzoeBFW8jYwVZGr+OMxjgZCTTopqB/vO//CI4aVHB2pE9Jw4cNA6Rl8uWo
 SRXJXBWIw6nKElpTvqjV2PQXiOFqssfW5asjedzHfwpeJucjk3q59K54/RG19EUs
 uqFVoElQMMiJ8QPlb91gYWH4AAdoc/G+YQkxlwt95638U6TKX/5FHc02glvgMNtI
 EYt4/Aavn/NQLGUMeDF2IxptUCbr4F7GcSkYgYFeaYWPssgOAkMdtxyDT9SwwEt5
 Oyq27CJ9TGPzdjRACteR+NUm6I5wOsy/mLX54BoumUGrApYtZzIvJDDEmIuWDzl8
 OdrSR1+D9oi31gcL4qMJEIAe4s+ALJ/witFcdAoEXPugZsV4mkjBB7sEew1qrha9
 WovyVsqlTnKtpNaoqPWH6jdBdsW49YsEVLVxsS5BT+48ZAYQEDXcAHJ1t65mQfsk
 0c9hIwiOgt5Y1nNe0CMaQ6zLpzBRhf+wUAsg/fDZgB/P0O+Yg9XnGlNqL6WPV9xP
 HK3PVgabzYcAr+ahEwvN3Ng5SE1FJ5xUv6kXhnVVjkOrfCMbgrckNHHVr4mvzK0n
 E4VlqRGrSzfSqE7RuS2s
 =GROK
 -----END PGP SIGNATURE-----

Merge tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux

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)
This commit is contained in:
Linus Torvalds 2015-01-14 11:54:12 +13:00
commit 0c133dd00e
1 changed files with 6 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
include/linux/compiler.h
View File

@ -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__ */