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-rw-r--r--lib/Kconfig10
-rw-r--r--lib/lockref.c60
2 files changed, 69 insertions, 1 deletions
diff --git a/lib/Kconfig b/lib/Kconfig
index 71d9f81f6eed..65561716c16c 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -48,6 +48,16 @@ config STMP_DEVICE
config PERCPU_RWSEM
boolean
+config ARCH_USE_CMPXCHG_LOCKREF
+ bool
+
+config CMPXCHG_LOCKREF
+ def_bool y if ARCH_USE_CMPXCHG_LOCKREF
+ depends on SMP
+ depends on !GENERIC_LOCKBREAK
+ depends on !DEBUG_SPINLOCK
+ depends on !DEBUG_LOCK_ALLOC
+
config CRC_CCITT
tristate "CRC-CCITT functions"
help
diff --git a/lib/lockref.c b/lib/lockref.c
index a9a4f4e1eff5..7819c2d1d315 100644
--- a/lib/lockref.c
+++ b/lib/lockref.c
@@ -1,6 +1,33 @@
#include <linux/export.h>
#include <linux/lockref.h>
+#ifdef CONFIG_CMPXCHG_LOCKREF
+
+/*
+ * Note that the "cmpxchg()" reloads the "old" value for the
+ * failure case.
+ */
+#define CMPXCHG_LOOP(CODE, SUCCESS) do { \
+ struct lockref old; \
+ BUILD_BUG_ON(sizeof(old) != 8); \
+ old.lock_count = ACCESS_ONCE(lockref->lock_count); \
+ 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); \
+ if (likely(old.lock_count == prev.lock_count)) { \
+ SUCCESS; \
+ } \
+ } \
+} while (0)
+
+#else
+
+#define CMPXCHG_LOOP(CODE, SUCCESS) do { } while (0)
+
+#endif
+
/**
* lockref_get - Increments reference count unconditionally
* @lockcnt: pointer to lockref structure
@@ -10,6 +37,12 @@
*/
void lockref_get(struct lockref *lockref)
{
+ CMPXCHG_LOOP(
+ new.count++;
+ ,
+ return;
+ );
+
spin_lock(&lockref->lock);
lockref->count++;
spin_unlock(&lockref->lock);
@@ -23,9 +56,18 @@ EXPORT_SYMBOL(lockref_get);
*/
int lockref_get_not_zero(struct lockref *lockref)
{
- int retval = 0;
+ int retval;
+
+ CMPXCHG_LOOP(
+ new.count++;
+ if (!old.count)
+ return 0;
+ ,
+ return 1;
+ );
spin_lock(&lockref->lock);
+ retval = 0;
if (lockref->count) {
lockref->count++;
retval = 1;
@@ -43,6 +85,14 @@ EXPORT_SYMBOL(lockref_get_not_zero);
*/
int lockref_get_or_lock(struct lockref *lockref)
{
+ CMPXCHG_LOOP(
+ new.count++;
+ if (!old.count)
+ break;
+ ,
+ return 1;
+ );
+
spin_lock(&lockref->lock);
if (!lockref->count)
return 0;
@@ -59,6 +109,14 @@ EXPORT_SYMBOL(lockref_get_or_lock);
*/
int lockref_put_or_lock(struct lockref *lockref)
{
+ CMPXCHG_LOOP(
+ new.count--;
+ if (old.count <= 1)
+ break;
+ ,
+ return 1;
+ );
+
spin_lock(&lockref->lock);
if (lockref->count <= 1)
return 0;