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lockref: use cmpxchg64 explicitly for lockless updates 

The cmpxchg() function tends not to support 64-bit arguments on 32-bit
architectures.  This could be either due to use of unsigned long
arguments (like on ARM) or lack of instruction support (cmpxchgq on
x86).  However, these architectures may implement a specific cmpxchg64()
function to provide 64-bit cmpxchg support instead.

Since the lockref code requires a 64-bit cmpxchg and relies on the
architecture selecting ARCH_USE_CMPXCHG_LOCKREF, move to using cmpxchg64
instead of cmpxchg and allow 32-bit architectures to make use of the
lockless lockref implementation.

Cc: Waiman Long <Waiman.Long@hp.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Will Deacon 2013-09-19 19:06:46 +01:00 committed by Linus Torvalds
parent dcb30e6592
commit 8f4c344696
1 changed files with 2 additions and 2 deletions
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4
lib/lockref.c
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@ -14,8 +14,8 @@
while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \
struct lockref new = old, prev = old; \
CODE \
old.lock_count = cmpxchg(&lockref->lock_count, \
old.lock_count, new.lock_count); \
old.lock_count = cmpxchg64(&lockref->lock_count, \
old.lock_count, new.lock_count); \
if (likely(old.lock_count == prev.lock_count)) { \
SUCCESS; \
} \