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-rw-r--r--arch/x86/include/asm/spinlock.h90
-rw-r--r--arch/x86/kernel/kvm.c13
-rw-r--r--arch/x86/xen/spinlock.c13
-rw-r--r--kernel/locking/rtmutex.c3
4 files changed, 64 insertions, 55 deletions
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 7050d864f520..cf87de3fc390 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -46,7 +46,7 @@ static __always_inline bool static_key_false(struct static_key *key);
static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
{
- set_bit(0, (volatile unsigned long *)&lock->tickets.tail);
+ set_bit(0, (volatile unsigned long *)&lock->tickets.head);
}
#else /* !CONFIG_PARAVIRT_SPINLOCKS */
@@ -60,10 +60,30 @@ static inline void __ticket_unlock_kick(arch_spinlock_t *lock,
}
#endif /* CONFIG_PARAVIRT_SPINLOCKS */
+static inline int __tickets_equal(__ticket_t one, __ticket_t two)
+{
+ return !((one ^ two) & ~TICKET_SLOWPATH_FLAG);
+}
+
+static inline void __ticket_check_and_clear_slowpath(arch_spinlock_t *lock,
+ __ticket_t head)
+{
+ if (head & TICKET_SLOWPATH_FLAG) {
+ arch_spinlock_t old, new;
+
+ old.tickets.head = head;
+ new.tickets.head = head & ~TICKET_SLOWPATH_FLAG;
+ old.tickets.tail = new.tickets.head + TICKET_LOCK_INC;
+ new.tickets.tail = old.tickets.tail;
+
+ /* try to clear slowpath flag when there are no contenders */
+ cmpxchg(&lock->head_tail, old.head_tail, new.head_tail);
+ }
+}
static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
{
- return lock.tickets.head == lock.tickets.tail;
+ return __tickets_equal(lock.tickets.head, lock.tickets.tail);
}
/*
@@ -87,18 +107,21 @@ static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
if (likely(inc.head == inc.tail))
goto out;
- inc.tail &= ~TICKET_SLOWPATH_FLAG;
for (;;) {
unsigned count = SPIN_THRESHOLD;
do {
- if (READ_ONCE(lock->tickets.head) == inc.tail)
- goto out;
+ inc.head = READ_ONCE(lock->tickets.head);
+ if (__tickets_equal(inc.head, inc.tail))
+ goto clear_slowpath;
cpu_relax();
} while (--count);
__ticket_lock_spinning(lock, inc.tail);
}
-out: barrier(); /* make sure nothing creeps before the lock is taken */
+clear_slowpath:
+ __ticket_check_and_clear_slowpath(lock, inc.head);
+out:
+ barrier(); /* make sure nothing creeps before the lock is taken */
}
static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
@@ -106,56 +129,30 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
arch_spinlock_t old, new;
old.tickets = READ_ONCE(lock->tickets);
- if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG))
+ if (!__tickets_equal(old.tickets.head, old.tickets.tail))
return 0;
new.head_tail = old.head_tail + (TICKET_LOCK_INC << TICKET_SHIFT);
+ new.head_tail &= ~TICKET_SLOWPATH_FLAG;
/* cmpxchg is a full barrier, so nothing can move before it */
return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) == old.head_tail;
}
-static inline void __ticket_unlock_slowpath(arch_spinlock_t *lock,
- arch_spinlock_t old)
-{
- arch_spinlock_t new;
-
- BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS);
-
- /* Perform the unlock on the "before" copy */
- old.tickets.head += TICKET_LOCK_INC;
-
- /* Clear the slowpath flag */
- new.head_tail = old.head_tail & ~(TICKET_SLOWPATH_FLAG << TICKET_SHIFT);
-
- /*
- * If the lock is uncontended, clear the flag - use cmpxchg in
- * case it changes behind our back though.
- */
- if (new.tickets.head != new.tickets.tail ||
- cmpxchg(&lock->head_tail, old.head_tail,
- new.head_tail) != old.head_tail) {
- /*
- * Lock still has someone queued for it, so wake up an
- * appropriate waiter.
- */
- __ticket_unlock_kick(lock, old.tickets.head);
- }
-}
-
static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
{
if (TICKET_SLOWPATH_FLAG &&
- static_key_false(&paravirt_ticketlocks_enabled)) {
- arch_spinlock_t prev;
+ static_key_false(&paravirt_ticketlocks_enabled)) {
+ __ticket_t head;
- prev = *lock;
- add_smp(&lock->tickets.head, TICKET_LOCK_INC);
+ BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS);
- /* add_smp() is a full mb() */
+ head = xadd(&lock->tickets.head, TICKET_LOCK_INC);
- if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG))
- __ticket_unlock_slowpath(lock, prev);
+ if (unlikely(head & TICKET_SLOWPATH_FLAG)) {
+ head &= ~TICKET_SLOWPATH_FLAG;
+ __ticket_unlock_kick(lock, (head + TICKET_LOCK_INC));
+ }
} else
__add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
}
@@ -164,14 +161,15 @@ static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
struct __raw_tickets tmp = READ_ONCE(lock->tickets);
- return tmp.tail != tmp.head;
+ return !__tickets_equal(tmp.tail, tmp.head);
}
static inline int arch_spin_is_contended(arch_spinlock_t *lock)
{
struct __raw_tickets tmp = READ_ONCE(lock->tickets);
- return (__ticket_t)(tmp.tail - tmp.head) > TICKET_LOCK_INC;
+ tmp.head &= ~TICKET_SLOWPATH_FLAG;
+ return (tmp.tail - tmp.head) > TICKET_LOCK_INC;
}
#define arch_spin_is_contended arch_spin_is_contended
@@ -191,8 +189,8 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
* We need to check "unlocked" in a loop, tmp.head == head
* can be false positive because of overflow.
*/
- if (tmp.head == (tmp.tail & ~TICKET_SLOWPATH_FLAG) ||
- tmp.head != head)
+ if (__tickets_equal(tmp.head, tmp.tail) ||
+ !__tickets_equal(tmp.head, head))
break;
cpu_relax();
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 94f643484300..e354cc6446ab 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -609,7 +609,7 @@ static inline void check_zero(void)
u8 ret;
u8 old;
- old = ACCESS_ONCE(zero_stats);
+ old = READ_ONCE(zero_stats);
if (unlikely(old)) {
ret = cmpxchg(&zero_stats, old, 0);
/* This ensures only one fellow resets the stat */
@@ -727,6 +727,7 @@ __visible void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
int cpu;
u64 start;
unsigned long flags;
+ __ticket_t head;
if (in_nmi())
return;
@@ -768,11 +769,15 @@ __visible void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
*/
__ticket_enter_slowpath(lock);
+ /* make sure enter_slowpath, which is atomic does not cross the read */
+ smp_mb__after_atomic();
+
/*
* check again make sure it didn't become free while
* we weren't looking.
*/
- if (ACCESS_ONCE(lock->tickets.head) == want) {
+ head = READ_ONCE(lock->tickets.head);
+ if (__tickets_equal(head, want)) {
add_stats(TAKEN_SLOW_PICKUP, 1);
goto out;
}
@@ -803,8 +808,8 @@ static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
add_stats(RELEASED_SLOW, 1);
for_each_cpu(cpu, &waiting_cpus) {
const struct kvm_lock_waiting *w = &per_cpu(klock_waiting, cpu);
- if (ACCESS_ONCE(w->lock) == lock &&
- ACCESS_ONCE(w->want) == ticket) {
+ if (READ_ONCE(w->lock) == lock &&
+ READ_ONCE(w->want) == ticket) {
add_stats(RELEASED_SLOW_KICKED, 1);
kvm_kick_cpu(cpu);
break;
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 23b45eb9a89c..956374c1edbc 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -41,7 +41,7 @@ static u8 zero_stats;
static inline void check_zero(void)
{
u8 ret;
- u8 old = ACCESS_ONCE(zero_stats);
+ u8 old = READ_ONCE(zero_stats);
if (unlikely(old)) {
ret = cmpxchg(&zero_stats, old, 0);
/* This ensures only one fellow resets the stat */
@@ -112,6 +112,7 @@ __visible void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
struct xen_lock_waiting *w = this_cpu_ptr(&lock_waiting);
int cpu = smp_processor_id();
u64 start;
+ __ticket_t head;
unsigned long flags;
/* If kicker interrupts not initialized yet, just spin */
@@ -159,11 +160,15 @@ __visible void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
*/
__ticket_enter_slowpath(lock);
+ /* make sure enter_slowpath, which is atomic does not cross the read */
+ smp_mb__after_atomic();
+
/*
* check again make sure it didn't become free while
* we weren't looking
*/
- if (ACCESS_ONCE(lock->tickets.head) == want) {
+ head = READ_ONCE(lock->tickets.head);
+ if (__tickets_equal(head, want)) {
add_stats(TAKEN_SLOW_PICKUP, 1);
goto out;
}
@@ -204,8 +209,8 @@ static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next)
const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu);
/* Make sure we read lock before want */
- if (ACCESS_ONCE(w->lock) == lock &&
- ACCESS_ONCE(w->want) == next) {
+ if (READ_ONCE(w->lock) == lock &&
+ READ_ONCE(w->want) == next) {
add_stats(RELEASED_SLOW_KICKED, 1);
xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
break;
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 3059bc2f022d..e16e5542bf13 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1193,7 +1193,8 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
if (unlikely(ret)) {
- remove_waiter(lock, &waiter);
+ if (rt_mutex_has_waiters(lock))
+ remove_waiter(lock, &waiter);
rt_mutex_handle_deadlock(ret, chwalk, &waiter);
}