A-Team_Digital_Solutions/android_kernel_motorola_sm6375
Watch
2
0
Fork
You've already forked android_kernel_motorola_sm6375
 0
mirror of https://github.com/BobTheBlinker/android_kernel_motorola_sm6375.git synced 2026-10-25 22:23:14 -04:00
Code Issues Projects Releases Packages Wiki Activity

kernel: Provide READ_ONCE and ASSIGN_ONCE

Browse source 
As discussed on LKML http://marc.info/?i=54611D86.4040306%40de.ibm.com
 ACCESS_ONCE might fail with specific compilers for non-scalar accesses.
 
 Here is a set of patches to tackle that problem.
 
 The first patch introduce READ_ONCE and ASSIGN_ONCE. If the data structure
 is larger than the machine word size memcpy is used and a warning is emitted.
 The next patches fix up several in-tree users of ACCESS_ONCE on non-scalar
 types.
 
 This merge does not yet contain a patch that forces ACCESS_ONCE to work only
 on scalar types. This is targetted for the next merge window as Linux next
 already contains new offenders regarding ACCESS_ONCE vs. non-scalar types.
 -----BEGIN PGP SIGNATURE-----
 Version: GnuPG v2.0.14 (GNU/Linux)
 
 iQIcBAABAgAGBQJUkrVGAAoJEBF7vIC1phx8stkP/2LmN5y6LOseoEW06xa5MX4m
 cbIKsZNtsGHl7EDcTzzuWs6Sq5/Cj7V3yzeBF7QGbUKOqvFWU3jvpUBCCfjMg37C
 77/Vf0ZPrxTXXxeJ4Ykdy2CGvuMtuYY9TWkrRNKmLU0xex7lGblEzCt9z6+mZviw
 26/DN8ctjkHRvIUAi+7RfQBBc3oSMYAC1mzxYKBAsAFLV+LyFmsGU/4iofZMAsdt
 XFyVXlrLn0Bjx/MeceGkOlMDiVx4FnfccfFaD4hhuTLBJXWitkUK/MRa4JBiXWzH
 agY8942A8/j9wkI2DFp/pqZYqA/sTXLndyOWlhE//ZSti0n0BSJaOx3S27rTLkAc
 5VmZEVyIrS3hyOpyyAi0sSoPkDnjeCHmQg9Rqn34/poKLd7JDrW2UkERNCf/T3eh
 GI2rbhAlZz3v5mIShn8RrxzslWYmOObpMr3HYNUdRk8YUfTf6d6aZ3txHp2nP4mD
 VBAEzsvP9rcVT2caVhU2dnBzeaZAj3zeDxBtjcb3X2osY9tI7qgLc9Fa/fWKgILk
 2evkLcctsae2mlLNGHyaK3Dm/ZmYJv+57MyaQQEZNfZZgeB1y4k0DkxH4w1CFmCi
 s8XlH5voEHgnyjSQXXgc/PNVlkPAKr78ZyTiAfiKmh8rpe41/W4hGcgao7L9Lgiu
 SI0uSwKibuZt4dHGxQuG
 =IQ5o
 -----END PGP SIGNATURE-----

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

Pull ACCESS_ONCE cleanup preparation from Christian Borntraeger:
 "kernel: Provide READ_ONCE and ASSIGN_ONCE

  As discussed on LKML http://marc.info/?i=54611D86.4040306%40de.ibm.com
  ACCESS_ONCE might fail with specific compilers for non-scalar
  accesses.

  Here is a set of patches to tackle that problem.

  The first patch introduce READ_ONCE and ASSIGN_ONCE.  If the data
  structure is larger than the machine word size memcpy is used and a
  warning is emitted.  The next patches fix up several in-tree users of
  ACCESS_ONCE on non-scalar types.

  This does not yet contain a patch that forces ACCESS_ONCE to work only
  on scalar types.  This is targetted for the next merge window as Linux
  next already contains new offenders regarding ACCESS_ONCE vs.
  non-scalar types"

* tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux:
  s390/kvm: REPLACE barrier fixup with READ_ONCE
  arm/spinlock: Replace ACCESS_ONCE with READ_ONCE
  arm64/spinlock: Replace ACCESS_ONCE READ_ONCE
  mips/gup: Replace ACCESS_ONCE with READ_ONCE
  x86/gup: Replace ACCESS_ONCE with READ_ONCE
  x86/spinlock: Replace ACCESS_ONCE with READ_ONCE
  mm: replace ACCESS_ONCE with READ_ONCE or barriers
  kernel: Provide READ_ONCE and ASSIGN_ONCE
This commit is contained in:
Linus Torvalds 2014-12-20 16:48:59 -08:00
commit 60815cf2e0
10 changed files with 103 additions and 25 deletions
Download patch file Download diff file Expand all files Collapse all files

74
include/linux/compiler.h
View file

@ -186,6 +186,80 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
# define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __LINE__)
#endif
#include <uapi/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)
{
switch (size) {
case 1: *(__u8 *)res = *(volatile __u8 *)p; break;
case 2: *(__u16 *)res = *(volatile __u16 *)p; break;
case 4: *(__u32 *)res = *(volatile __u32 *)p; break;
#ifdef CONFIG_64BIT
case 8: *(__u64 *)res = *(volatile __u64 *)p; break;
#endif
default:
barrier();
__builtin_memcpy((void *)res, (const void *)p, size);
data_access_exceeds_word_size();
barrier();
}
}
static __always_inline void __assign_once_size(volatile void *p, void *res, int size)
{
switch (size) {
case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
case 2: *(volatile __u16 *)p = *(__u16 *)res; break;
case 4: *(volatile __u32 *)p = *(__u32 *)res; break;
#ifdef CONFIG_64BIT
case 8: *(volatile __u64 *)p = *(__u64 *)res; break;
#endif
default:
barrier();
__builtin_memcpy((void *)p, (const void *)res, size);
data_access_exceeds_word_size();
barrier();
}
}
/*
* 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
* 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.
*
* 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
* compile-time warning.
*
* Their two major use cases are: (1) Mediating communication between
* process-level code and irq/NMI handlers, all running on the same CPU,
* and (2) Ensuring that the compiler does not fold, spindle, or otherwise
* mutilate accesses that either do not require ordering or that interact
* with an explicit memory barrier or atomic instruction that provides the
* required ordering.
*/
#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; })
#endif /* __KERNEL__ */
#endif /* __ASSEMBLY__ */