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>

diff --git a/lib/lockref.c b/lib/lockref.c
index dc30f27..b0b8e97 100644 (file)
--- a/lib/lockref.c
+++ b/lib/lockref.c
@@ -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;                                                \
                }                                                               \