xen: bug fixes for 4.2-rc5

- Don't lose interrupts when offlining CPUs.
 - Fix gntdev oops during unmap.
 - Drop the balloon lock occasionally to allow domain create/destroy.
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Merge tag 'for-linus-4.2-rc5-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip

Pull xen bug fixes from David Vrabel:

 - don't lose interrupts when offlining CPUs

 - fix gntdev oops during unmap

 - drop the balloon lock occasionally to allow domain create/destroy

* tag 'for-linus-4.2-rc5-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
  xen/events/fifo: Handle linked events when closing a port
  xen: release lock occasionally during ballooning
  xen/gntdevt: Fix race condition in gntdev_release()

drivers/xen/balloon.c

@@ -472,7 +472,7 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 }
 
 /*
- * We avoid multiple worker processes conflicting via the balloon mutex.
+ * As this is a work item it is guaranteed to run as a single instance only.
  * We may of course race updates of the target counts (which are protected
  * by the balloon lock), or with changes to the Xen hard limit, but we will
  * recover from these in time.
@@ -482,9 +482,10 @@ static void balloon_process(struct work_struct *work)
 	enum bp_state state = BP_DONE;
 	long credit;
 
-	mutex_lock(&balloon_mutex);
 
 	do {
+		mutex_lock(&balloon_mutex);
+
 		credit = current_credit();
 
 		if (credit > 0) {
@@ -499,17 +500,15 @@ static void balloon_process(struct work_struct *work)
 
 		state = update_schedule(state);
 
-#ifndef CONFIG_PREEMPT
-		if (need_resched())
-			schedule();
-#endif
+		mutex_unlock(&balloon_mutex);
+
+		cond_resched();
+
 	} while (credit && state == BP_DONE);
 
 	/* Schedule more work if there is some still to be done. */
 	if (state == BP_EAGAIN)
 		schedule_delayed_work(&balloon_worker, balloon_stats.schedule_delay * HZ);
-
-	mutex_unlock(&balloon_mutex);
 }
 
 /* Resets the Xen limit, sets new target, and kicks off processing. */

drivers/xen/events/events_base.c

@@ -452,10 +452,12 @@ static void xen_free_irq(unsigned irq)
 	irq_free_desc(irq);
 }
 
-static void xen_evtchn_close(unsigned int port)
+static void xen_evtchn_close(unsigned int port, unsigned int cpu)
 {
 	struct evtchn_close close;
 
+	xen_evtchn_op_close(port, cpu);
+
 	close.port = port;
 	if (HYPERVISOR_event_channel_op(EVTCHNOP_close, &close) != 0)
 		BUG();
@@ -544,7 +546,7 @@ out:
 
 err:
 	pr_err("irq%d: Failed to set port to irq mapping (%d)\n", irq, rc);
-	xen_evtchn_close(evtchn);
+	xen_evtchn_close(evtchn, NR_CPUS);
 	return 0;
 }
 
@@ -565,7 +567,7 @@ static void shutdown_pirq(struct irq_data *data)
 		return;
 
 	mask_evtchn(evtchn);
-	xen_evtchn_close(evtchn);
+	xen_evtchn_close(evtchn, cpu_from_evtchn(evtchn));
 	xen_irq_info_cleanup(info);
 }
 
@@ -609,7 +611,7 @@ static void __unbind_from_irq(unsigned int irq)
 	if (VALID_EVTCHN(evtchn)) {
 		unsigned int cpu = cpu_from_irq(irq);
 
-		xen_evtchn_close(evtchn);
+		xen_evtchn_close(evtchn, cpu);
 
 		switch (type_from_irq(irq)) {
 		case IRQT_VIRQ:

drivers/xen/events/events_fifo.c

@@ -255,6 +255,12 @@ static void evtchn_fifo_unmask(unsigned port)
 	}
 }
 
+static bool evtchn_fifo_is_linked(unsigned port)
+{
+	event_word_t *word = event_word_from_port(port);
+	return sync_test_bit(EVTCHN_FIFO_BIT(LINKED, word), BM(word));
+}
+
 static uint32_t clear_linked(volatile event_word_t *word)
 {
 	event_word_t new, old, w;
@@ -281,7 +287,8 @@ static void handle_irq_for_port(unsigned port)
 
 static void consume_one_event(unsigned cpu,
 			      struct evtchn_fifo_control_block *control_block,
-			      unsigned priority, unsigned long *ready)
+			      unsigned priority, unsigned long *ready,
+			      bool drop)
 {
 	struct evtchn_fifo_queue *q = &per_cpu(cpu_queue, cpu);
 	uint32_t head;
@@ -313,13 +320,15 @@ static void consume_one_event(unsigned cpu,
 	if (head == 0)
 		clear_bit(priority, ready);
 
-	if (evtchn_fifo_is_pending(port) && !evtchn_fifo_is_masked(port))
-		handle_irq_for_port(port);
+	if (evtchn_fifo_is_pending(port) && !evtchn_fifo_is_masked(port)) {
+		if (likely(!drop))
+			handle_irq_for_port(port);
+	}
 
 	q->head[priority] = head;
 }
 
-static void evtchn_fifo_handle_events(unsigned cpu)
+static void __evtchn_fifo_handle_events(unsigned cpu, bool drop)
 {
 	struct evtchn_fifo_control_block *control_block;
 	unsigned long ready;
@@ -331,11 +340,16 @@ static void evtchn_fifo_handle_events(unsigned cpu)
 
 	while (ready) {
 		q = find_first_bit(&ready, EVTCHN_FIFO_MAX_QUEUES);
-		consume_one_event(cpu, control_block, q, &ready);
+		consume_one_event(cpu, control_block, q, &ready, drop);
 		ready |= xchg(&control_block->ready, 0);
 	}
 }
 
+static void evtchn_fifo_handle_events(unsigned cpu)
+{
+	__evtchn_fifo_handle_events(cpu, false);
+}
+
 static void evtchn_fifo_resume(void)
 {
 	unsigned cpu;
@@ -371,6 +385,26 @@ static void evtchn_fifo_resume(void)
 	event_array_pages = 0;
 }
 
+static void evtchn_fifo_close(unsigned port, unsigned int cpu)
+{
+	if (cpu == NR_CPUS)
+		return;
+
+	get_online_cpus();
+	if (cpu_online(cpu)) {
+		if (WARN_ON(irqs_disabled()))
+			goto out;
+
+		while (evtchn_fifo_is_linked(port))
+			cpu_relax();
+	} else {
+		__evtchn_fifo_handle_events(cpu, true);
+	}
+
+out:
+	put_online_cpus();
+}
+
 static const struct evtchn_ops evtchn_ops_fifo = {
 	.max_channels      = evtchn_fifo_max_channels,
 	.nr_channels       = evtchn_fifo_nr_channels,
@@ -384,6 +418,7 @@ static const struct evtchn_ops evtchn_ops_fifo = {
 	.unmask            = evtchn_fifo_unmask,
 	.handle_events     = evtchn_fifo_handle_events,
 	.resume            = evtchn_fifo_resume,
+	.close             = evtchn_fifo_close,
 };
 
 static int evtchn_fifo_alloc_control_block(unsigned cpu)

drivers/xen/events/events_internal.h

@@ -68,6 +68,7 @@ struct evtchn_ops {
 	bool (*test_and_set_mask)(unsigned port);
 	void (*mask)(unsigned port);
 	void (*unmask)(unsigned port);
+	void (*close)(unsigned port, unsigned cpu);
 
 	void (*handle_events)(unsigned cpu);
 	void (*resume)(void);
@@ -145,6 +146,12 @@ static inline void xen_evtchn_resume(void)
 		evtchn_ops->resume();
 }
 
+static inline void xen_evtchn_op_close(unsigned port, unsigned cpu)
+{
+	if (evtchn_ops->close)
+		return evtchn_ops->close(port, cpu);
+}
+
 void xen_evtchn_2l_init(void);
 int xen_evtchn_fifo_init(void);
 

drivers/xen/gntdev.c

@@ -568,12 +568,14 @@ static int gntdev_release(struct inode *inode, struct file *flip)
 
 	pr_debug("priv %p\n", priv);
 
+	mutex_lock(&priv->lock);
 	while (!list_empty(&priv->maps)) {
 		map = list_entry(priv->maps.next, struct grant_map, next);
 		list_del(&map->next);
 		gntdev_put_map(NULL /* already removed */, map);
 	}
 	WARN_ON(!list_empty(&priv->freeable_maps));
+	mutex_unlock(&priv->lock);
 
 	if (use_ptemod)
 		mmu_notifier_unregister(&priv->mn, priv->mm);