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-rw-r--r--arch/x86/include/asm/paravirt.h2
-rw-r--r--arch/x86/include/asm/spinlock.h86
-rw-r--r--arch/x86/include/asm/spinlock_types.h2
-rw-r--r--arch/x86/kernel/paravirt-spinlocks.c3
-rw-r--r--arch/x86/xen/spinlock.c6
5 files changed, 74 insertions, 25 deletions
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 7131e12c..401f350 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -718,7 +718,7 @@ static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
PVOP_VCALLEE2(pv_lock_ops.lock_spinning, lock, ticket);
}
-static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock,
+static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock,
__ticket_t ticket)
{
PVOP_VCALL2(pv_lock_ops.unlock_kick, lock, ticket);
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 04a5cd5..d68883d 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -1,11 +1,14 @@
#ifndef _ASM_X86_SPINLOCK_H
#define _ASM_X86_SPINLOCK_H
+#include <linux/jump_label.h>
#include <linux/atomic.h>
#include <asm/page.h>
#include <asm/processor.h>
#include <linux/compiler.h>
#include <asm/paravirt.h>
+#include <asm/bitops.h>
+
/*
* Your basic SMP spinlocks, allowing only a single CPU anywhere
*
@@ -37,32 +40,28 @@
/* How long a lock should spin before we consider blocking */
#define SPIN_THRESHOLD (1 << 15)
-#ifndef CONFIG_PARAVIRT_SPINLOCKS
+extern struct static_key paravirt_ticketlocks_enabled;
+static __always_inline bool static_key_false(struct static_key *key);
-static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
- __ticket_t ticket)
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+
+static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
{
+ set_bit(0, (volatile unsigned long *)&lock->tickets.tail);
}
-static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock,
- __ticket_t ticket)
+#else /* !CONFIG_PARAVIRT_SPINLOCKS */
+static __always_inline void __ticket_lock_spinning(arch_spinlock_t *lock,
+ __ticket_t ticket)
{
}
-
-#endif /* CONFIG_PARAVIRT_SPINLOCKS */
-
-
-/*
- * If a spinlock has someone waiting on it, then kick the appropriate
- * waiting cpu.
- */
-static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock,
- __ticket_t next)
+static inline void __ticket_unlock_kick(arch_spinlock_t *lock,
+ __ticket_t ticket)
{
- if (unlikely(lock->tickets.tail != next))
- ____ticket_unlock_kick(lock, next);
}
+#endif /* CONFIG_PARAVIRT_SPINLOCKS */
+
/*
* 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
@@ -76,20 +75,22 @@ static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock,
* in the high part, because a wide xadd increment of the low part would carry
* up and contaminate the high part.
*/
-static __always_inline void arch_spin_lock(struct arch_spinlock *lock)
+static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
{
register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC };
inc = xadd(&lock->tickets, inc);
+ if (likely(inc.head == inc.tail))
+ goto out;
+ inc.tail &= ~TICKET_SLOWPATH_FLAG;
for (;;) {
unsigned count = SPIN_THRESHOLD;
do {
- if (inc.head == inc.tail)
+ if (ACCESS_ONCE(lock->tickets.head) == inc.tail)
goto out;
cpu_relax();
- inc.head = ACCESS_ONCE(lock->tickets.head);
} while (--count);
__ticket_lock_spinning(lock, inc.tail);
}
@@ -101,7 +102,7 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
arch_spinlock_t old, new;
old.tickets = ACCESS_ONCE(lock->tickets);
- if (old.tickets.head != old.tickets.tail)
+ if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG))
return 0;
new.head_tail = old.head_tail + (TICKET_LOCK_INC << TICKET_SHIFT);
@@ -110,12 +111,49 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
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)
{
- __ticket_t next = lock->tickets.head + TICKET_LOCK_INC;
+ if (TICKET_SLOWPATH_FLAG &&
+ static_key_false(&paravirt_ticketlocks_enabled)) {
+ arch_spinlock_t prev;
+
+ prev = *lock;
+ add_smp(&lock->tickets.head, TICKET_LOCK_INC);
+
+ /* add_smp() is a full mb() */
- __add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
- __ticket_unlock_kick(lock, next);
+ if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG))
+ __ticket_unlock_slowpath(lock, prev);
+ } else
+ __add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
}
static inline int arch_spin_is_locked(arch_spinlock_t *lock)
diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h
index e96fcbd..4f1bea1 100644
--- a/arch/x86/include/asm/spinlock_types.h
+++ b/arch/x86/include/asm/spinlock_types.h
@@ -5,8 +5,10 @@
#ifdef CONFIG_PARAVIRT_SPINLOCKS
#define __TICKET_LOCK_INC 2
+#define TICKET_SLOWPATH_FLAG ((__ticket_t)1)
#else
#define __TICKET_LOCK_INC 1
+#define TICKET_SLOWPATH_FLAG ((__ticket_t)0)
#endif
#if (CONFIG_NR_CPUS < (256 / __TICKET_LOCK_INC))
diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c
index 4251c1d..bbb6c73 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -4,6 +4,7 @@
*/
#include <linux/spinlock.h>
#include <linux/module.h>
+#include <linux/jump_label.h>
#include <asm/paravirt.h>
@@ -15,3 +16,5 @@ struct pv_lock_ops pv_lock_ops = {
};
EXPORT_SYMBOL(pv_lock_ops);
+struct static_key paravirt_ticketlocks_enabled = STATIC_KEY_INIT_FALSE;
+EXPORT_SYMBOL(paravirt_ticketlocks_enabled);
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 6c8792b..546112e 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -157,6 +157,10 @@ static void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
/* Only check lock once pending cleared */
barrier();
+ /* Mark entry to slowpath before doing the pickup test to make
+ sure we don't deadlock with an unlocker. */
+ __ticket_enter_slowpath(lock);
+
/* check again make sure it didn't become free while
we weren't looking */
if (ACCESS_ONCE(lock->tickets.head) == want) {
@@ -261,6 +265,8 @@ void __init xen_init_spinlocks(void)
return;
}
+ static_key_slow_inc(&paravirt_ticketlocks_enabled);
+
pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
pv_lock_ops.unlock_kick = xen_unlock_kick;
}
generated by cgit v0.10.2 at 2024-09-07 12:28:57 (GMT)