The quilt patch titled
Subject: bitops: use try_cmpxchg in set_mask_bits and bit_clear_unless
has been removed from the -mm tree. Its filename was
bitops-use-try_cmpxchg-in-set_mask_bits-and-bit_clear_unless.patch
This patch was dropped because it was merged into the mm-nonmm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Uros Bizjak <ubizjak@xxxxxxxxx>
Subject: bitops: use try_cmpxchg in set_mask_bits and bit_clear_unless
Date: Mon, 22 Aug 2022 16:38:51 +0200
Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
set_mask_bits and bit_clear_unless. x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after cmpxchg (and
related move instruction in front of cmpxchg).
Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails, enabling further code simplifications.
Link: https://lkml.kernel.org/r/20220822143851.3290-1-ubizjak@xxxxxxxxx
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/bitops.h | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
--- a/include/linux/bitops.h~bitops-use-try_cmpxchg-in-set_mask_bits-and-bit_clear_unless
+++ a/include/linux/bitops.h
@@ -328,10 +328,10 @@ static __always_inline void __assign_bit
const typeof(*(ptr)) mask__ = (mask), bits__ = (bits); \
typeof(*(ptr)) old__, new__; \
\
+ old__ = READ_ONCE(*(ptr)); \
do { \
- old__ = READ_ONCE(*(ptr)); \
new__ = (old__ & ~mask__) | bits__; \
- } while (cmpxchg(ptr, old__, new__) != old__); \
+ } while (!try_cmpxchg(ptr, &old__, new__)); \
\
old__; \
})
@@ -343,11 +343,12 @@ static __always_inline void __assign_bit
const typeof(*(ptr)) clear__ = (clear), test__ = (test);\
typeof(*(ptr)) old__, new__; \
\
+ old__ = READ_ONCE(*(ptr)); \
do { \
- old__ = READ_ONCE(*(ptr)); \
+ if (old__ & test__) \
+ break; \
new__ = old__ & ~clear__; \
- } while (!(old__ & test__) && \
- cmpxchg(ptr, old__, new__) != old__); \
+ } while (!try_cmpxchg(ptr, &old__, new__)); \
\
!(old__ & test__); \
})
_
Patches currently in -mm which might be from ubizjak@xxxxxxxxx are
