---

yaml
---
r: 113245
b: refs/heads/master
c: 168d2f4
h: refs/heads/master
i:
  113243: e29c9c6
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 7708ad64a24a674f7905aa7a5099a50f055debec
+refs/heads/master: 168d2f464ab9860f0d1e66cf1f9684973222f1c6

trunk/arch/x86/xen/spinlock.c

@@ -47,25 +47,41 @@ static int xen_spin_trylock(struct raw_spinlock *lock)
 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
 static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners);
 
-static inline void spinning_lock(struct xen_spinlock *xl)
+/*
+ * Mark a cpu as interested in a lock.  Returns the CPU's previous
+ * lock of interest, in case we got preempted by an interrupt.
+ */
+static inline struct xen_spinlock *spinning_lock(struct xen_spinlock *xl)
 {
+	struct xen_spinlock *prev;
+
+	prev = __get_cpu_var(lock_spinners);
 	__get_cpu_var(lock_spinners) = xl;
+
 	wmb();			/* set lock of interest before count */
+
 	asm(LOCK_PREFIX " incw %0"
 	    : "+m" (xl->spinners) : : "memory");
+
+	return prev;
 }
 
-static inline void unspinning_lock(struct xen_spinlock *xl)
+/*
+ * Mark a cpu as no longer interested in a lock.  Restores previous
+ * lock of interest (NULL for none).
+ */
+static inline void unspinning_lock(struct xen_spinlock *xl, struct xen_spinlock *prev)
 {
 	asm(LOCK_PREFIX " decw %0"
 	    : "+m" (xl->spinners) : : "memory");
-	wmb();			/* decrement count before clearing lock */
-	__get_cpu_var(lock_spinners) = NULL;
+	wmb();			/* decrement count before restoring lock */
+	__get_cpu_var(lock_spinners) = prev;
 }
 
 static noinline int xen_spin_lock_slow(struct raw_spinlock *lock)
 {
 	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
+	struct xen_spinlock *prev;
 	int irq = __get_cpu_var(lock_kicker_irq);
 	int ret;
 
@@ -74,23 +90,42 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock)
 		return 0;
 
 	/* announce we're spinning */
-	spinning_lock(xl);
+	prev = spinning_lock(xl);
 
-	/* clear pending */
-	xen_clear_irq_pending(irq);
+	do {
+		/* clear pending */
+		xen_clear_irq_pending(irq);
+
+		/* check again make sure it didn't become free while
+		   we weren't looking  */
+		ret = xen_spin_trylock(lock);
+		if (ret) {
+			/*
+			 * If we interrupted another spinlock while it
+			 * was blocking, make sure it doesn't block
+			 * without rechecking the lock.
+			 */
+			if (prev != NULL)
+				xen_set_irq_pending(irq);
+			goto out;
+		}
 
-	/* check again make sure it didn't become free while
-	   we weren't looking  */
-	ret = xen_spin_trylock(lock);
-	if (ret)
-		goto out;
+		/*
+		 * Block until irq becomes pending.  If we're
+		 * interrupted at this point (after the trylock but
+		 * before entering the block), then the nested lock
+		 * handler guarantees that the irq will be left
+		 * pending if there's any chance the lock became free;
+		 * xen_poll_irq() returns immediately if the irq is
+		 * pending.
+		 */
+		xen_poll_irq(irq);
+	} while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */
 
-	/* block until irq becomes pending */
-	xen_poll_irq(irq);
 	kstat_this_cpu.irqs[irq]++;
 
 out:
-	unspinning_lock(xl);
+	unspinning_lock(xl, prev);
 	return ret;
 }
 

trunk/drivers/xen/events.c

@@ -164,6 +164,12 @@ static inline void set_evtchn(int port)
 	sync_set_bit(port, &s->evtchn_pending[0]);
 }
 
+static inline int test_evtchn(int port)
+{
+	struct shared_info *s = HYPERVISOR_shared_info;
+	return sync_test_bit(port, &s->evtchn_pending[0]);
+}
+
 
 /**
  * notify_remote_via_irq - send event to remote end of event channel via irq
@@ -732,6 +738,25 @@ void xen_clear_irq_pending(int irq)
 		clear_evtchn(evtchn);
 }
 
+void xen_set_irq_pending(int irq)
+{
+	int evtchn = evtchn_from_irq(irq);
+
+	if (VALID_EVTCHN(evtchn))
+		set_evtchn(evtchn);
+}
+
+bool xen_test_irq_pending(int irq)
+{
+	int evtchn = evtchn_from_irq(irq);
+	bool ret = false;
+
+	if (VALID_EVTCHN(evtchn))
+		ret = test_evtchn(evtchn);
+
+	return ret;
+}
+
 /* Poll waiting for an irq to become pending.  In the usual case, the
    irq will be disabled so it won't deliver an interrupt. */
 void xen_poll_irq(int irq)

trunk/include/xen/events.h

@@ -46,6 +46,8 @@ extern void xen_irq_resume(void);
 
 /* Clear an irq's pending state, in preparation for polling on it */
 void xen_clear_irq_pending(int irq);
+void xen_set_irq_pending(int irq);
+bool xen_test_irq_pending(int irq);
 
 /* Poll waiting for an irq to become pending.  In the usual case, the
    irq will be disabled so it won't deliver an interrupt. */