Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old
in get_acl. x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).
No functional change intended.
Signed-off-by: Uros Bizjak <[email protected]>
Cc: Alexander Viro <[email protected]>
---
fs/posix_acl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 962d32468eb4..49a13fd4d3cb 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -164,7 +164,7 @@ struct posix_acl *get_acl(struct inode *inode, int type)
* Cache the result, but only if our sentinel is still in place.
*/
posix_acl_dup(acl);
- if (unlikely(cmpxchg(p, sentinel, acl) != sentinel))
+ if (unlikely(!try_cmpxchg(p, &sentinel, acl)))
posix_acl_release(acl);
return acl;
}
--
2.35.3
Hi Uros,
Thank you for the patch! Yet something to improve:
[auto build test ERROR on linus/master]
[also build test ERROR on v5.19-rc6 next-20220715]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url:
https://github.com/intel-lab-lkp/linux/commits/Uros-Bizjak/posix_acl-Use-try_cmpxchg-in-get_acl/20220715-014002
base:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
4a57a8400075bc5287c5c877702c68aeae2a033d
config: powerpc-sam440ep_defconfig
(https://download.01.org/0day-ci/archive/20220716/[email protected]/config)
compiler: powerpc-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
wget
https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross
-O ~/bin/make.cross
chmod +x ~/bin/make.cross
#
https://github.com/intel-lab-lkp/linux/commit/8291d21630df3a57adf6d0ed8a1cded2a2700f66
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review
Uros-Bizjak/posix_acl-Use-try_cmpxchg-in-get_acl/20220715-014002
git checkout 8291d21630df3a57adf6d0ed8a1cded2a2700f66
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross
W=1 O=build_dir ARCH=powerpc SHELL=/bin/bash
If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <[email protected]>
All errors (new ones prefixed by >>):
In file included from include/linux/kernel.h:20,
from fs/posix_acl.c:14:
fs/posix_acl.c: In function 'get_acl':
>> include/linux/atomic/atomic-arch-fallback.h:90:34: error: initialization of 'struct posix_acl **' from incompatible pointer type 'void **' [-Werror=incompatible-pointer-types]
90 | typeof(*(_ptr)) *___op = (_oldp), ___o = *___op, ___r; \
| ^
include/linux/compiler.h:78:45: note: in definition of macro 'unlikely'
78 | # define unlikely(x) __builtin_expect(!!(x), 0)
| ^
include/linux/atomic/atomic-instrumented.h:1978:9: note: in
expansion of macro 'arch_try_cmpxchg'
1978 | arch_try_cmpxchg(__ai_ptr, __ai_oldp, __VA_ARGS__); \
| ^~~~~~~~~~~~~~~~
fs/posix_acl.c:167:23: note: in expansion of macro 'try_cmpxchg'
167 | if (unlikely(!try_cmpxchg(p, &sentinel, acl)))
| ^~~~~~~~~~~
cc1: some warnings being treated as errors
vim +90 include/linux/atomic/atomic-arch-fallback.h
29f006fdefe6f8 include/linux/atomic-arch-fallback.h Peter Zijlstra
2020-08-29 86 29f006fdefe6f8 include/linux/atomic-arch-fallback.h
Peter Zijlstra 2020-08-29 87 #ifndef arch_try_cmpxchg
29f006fdefe6f8 include/linux/atomic-arch-fallback.h Peter Zijlstra
2020-08-29 88 #define arch_try_cmpxchg(_ptr, _oldp, _new) \
29f006fdefe6f8 include/linux/atomic-arch-fallback.h Peter Zijlstra
2020-08-29 89 ({ \
29f006fdefe6f8 include/linux/atomic-arch-fallback.h Peter Zijlstra
2020-08-29 @90 typeof(*(_ptr)) *___op = (_oldp), ___o = *___op, ___r; \
29f006fdefe6f8 include/linux/atomic-arch-fallback.h Peter Zijlstra
2020-08-29 91 ___r = arch_cmpxchg((_ptr), ___o, (_new)); \
29f006fdefe6f8 include/linux/atomic-arch-fallback.h Peter Zijlstra
2020-08-29 92 if (unlikely(___r != ___o)) \
29f006fdefe6f8 include/linux/atomic-arch-fallback.h Peter Zijlstra
2020-08-29 93 *___op = ___r; \
29f006fdefe6f8 include/linux/atomic-arch-fallback.h Peter Zijlstra
2020-08-29 94 likely(___r == ___o); \
29f006fdefe6f8 include/linux/atomic-arch-fallback.h Peter Zijlstra
2020-08-29 95 })
29f006fdefe6f8 include/linux/atomic-arch-fallback.h Peter Zijlstra
2020-08-29 96 #endif /* arch_try_cmpxchg */
29f006fdefe6f8 include/linux/atomic-arch-fallback.h Peter Zijlstra
2020-08-29 97
--
0-DAY CI Kernel Test Service
https://01.org/lkp