Merge tag 'for-linus-5.14-rc6-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip

Pull xen fixes from Juergen Gross:
 "A small cleanup patch and a fix of a rare race in the Xen evtchn
  driver"

* tag 'for-linus-5.14-rc6-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
  xen/events: Fix race in set_evtchn_to_irq
  xen/events: remove redundant initialization of variable irq

1 files changed, 15 insertions, 7 deletions

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index d7e361fb0548..a78704ae3618 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -198,12 +198,12 @@ static void disable_dynirq(struct irq_data *data);
 
 static DEFINE_PER_CPU(unsigned int, irq_epoch);
 
-static void clear_evtchn_to_irq_row(unsigned row)
+static void clear_evtchn_to_irq_row(int *evtchn_row)
 {
 	unsigned col;
 
 	for (col = 0; col < EVTCHN_PER_ROW; col++)
-		WRITE_ONCE(evtchn_to_irq[row][col], -1);
+		WRITE_ONCE(evtchn_row[col], -1);
 }
 
 static void clear_evtchn_to_irq_all(void)
@@ -213,7 +213,7 @@ static void clear_evtchn_to_irq_all(void)
 	for (row = 0; row < EVTCHN_ROW(xen_evtchn_max_channels()); row++) {
 		if (evtchn_to_irq[row] == NULL)
 			continue;
-		clear_evtchn_to_irq_row(row);
+		clear_evtchn_to_irq_row(evtchn_to_irq[row]);
 	}
 }
 
@@ -221,6 +221,7 @@ static int set_evtchn_to_irq(evtchn_port_t evtchn, unsigned int irq)
 {
 	unsigned row;
 	unsigned col;
+	int *evtchn_row;
 
 	if (evtchn >= xen_evtchn_max_channels())
 		return -EINVAL;
@@ -233,11 +234,18 @@ static int set_evtchn_to_irq(evtchn_port_t evtchn, unsigned int irq)
 		if (irq == -1)
 			return 0;
 
-		evtchn_to_irq[row] = (int *)get_zeroed_page(GFP_KERNEL);
-		if (evtchn_to_irq[row] == NULL)
+		evtchn_row = (int *) __get_free_pages(GFP_KERNEL, 0);
+		if (evtchn_row == NULL)
 			return -ENOMEM;
 
-		clear_evtchn_to_irq_row(row);
+		clear_evtchn_to_irq_row(evtchn_row);
+
+		/*
+		 * We've prepared an empty row for the mapping. If a different
+		 * thread was faster inserting it, we can drop ours.
+		 */
+		if (cmpxchg(&evtchn_to_irq[row], NULL, evtchn_row) != NULL)
+			free_page((unsigned long) evtchn_row);
 	}
 
 	WRITE_ONCE(evtchn_to_irq[row][col], irq);
@@ -1009,7 +1017,7 @@ static void __unbind_from_irq(unsigned int irq)
 int xen_bind_pirq_gsi_to_irq(unsigned gsi,
 			     unsigned pirq, int shareable, char *name)
 {
-	int irq = -1;
+	int irq;
 	struct physdev_irq irq_op;
 	int ret;