diff options
| -rw-r--r-- | arch/x86/Kconfig | 1 | ||||
| -rw-r--r-- | arch/x86/include/asm/spinlock.h | 5 | ||||
| -rw-r--r-- | include/linux/lockref.h | 11 | ||||
| -rw-r--r-- | lib/Kconfig | 10 | ||||
| -rw-r--r-- | lib/lockref.c | 60 |
5 files changed, 84 insertions, 3 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index b32ebf92b0c..67e00740531 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -16,6 +16,7 @@ config X86_64 def_bool y depends on 64BIT select X86_DEV_DMA_OPS + select ARCH_USE_CMPXCHG_LOCKREF ### Arch settings config X86 diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h index e3ddd7db723..e0e668422c7 100644 --- a/arch/x86/include/asm/spinlock.h +++ b/arch/x86/include/asm/spinlock.h @@ -34,6 +34,11 @@ # define UNLOCK_LOCK_PREFIX #endif +static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock) +{ + return lock.tickets.head == lock.tickets.tail; +} + /* * Ticket locks are conceptually two parts, one indicating the current head of * the queue, and the other indicating the current tail. The lock is acquired diff --git a/include/linux/lockref.h b/include/linux/lockref.h index 4c0af31c8d4..ca07b5028b0 100644 --- a/include/linux/lockref.h +++ b/include/linux/lockref.h @@ -17,8 +17,15 @@ #include <linux/spinlock.h> struct lockref { - spinlock_t lock; - unsigned int count; + union { +#ifdef CONFIG_CMPXCHG_LOCKREF + aligned_u64 lock_count; +#endif + struct { + spinlock_t lock; + unsigned int count; + }; + }; }; extern void lockref_get(struct lockref *); diff --git a/lib/Kconfig b/lib/Kconfig index 71d9f81f6ee..65561716c16 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 a9a4f4e1eff..7819c2d1d31 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; |