[PATCH 2/2] xen/events: increment refcnt only if event channel is refcounted

[Juergen Gross <jgross@xxxxxxxx>]

In bind_evtchn_to_irq_chip() don't increment the refcnt of the event
channel blindly. In case the event channel is NOT refcounted, issue a
warning instead.

Add an additional safety net by doing the refcnt increment only if the
caller has specified IRQF_SHARED in the irqflags parameter.

Fixes: 9e90e58c11b7 ("xen: evtchn: Allow shared registration of IRQ handers")
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 drivers/xen/events/events_base.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 2faa4bf78c7a..81effbd53dc5 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -1190,7 +1190,7 @@ int xen_pirq_from_irq(unsigned irq)
 EXPORT_SYMBOL_GPL(xen_pirq_from_irq);
 
 static int bind_evtchn_to_irq_chip(evtchn_port_t evtchn, struct irq_chip *chip,
-                                  struct xenbus_device *dev)
+                                  struct xenbus_device *dev, bool shared)
 {
        int ret = -ENOMEM;
        struct irq_info *info;
@@ -1224,7 +1224,8 @@ static int bind_evtchn_to_irq_chip(evtchn_port_t evtchn, 
struct irq_chip *chip,
                 */
                bind_evtchn_to_cpu(info, 0, false);
        } else if (!WARN_ON(info->type != IRQT_EVTCHN)) {
-               info->refcnt++;
+               if (shared && !WARN_ON(info->refcnt < 0))
+                       info->refcnt++;
        }
 
        ret = info->irq;
@@ -1237,13 +1238,13 @@ static int bind_evtchn_to_irq_chip(evtchn_port_t 
evtchn, struct irq_chip *chip,
 
 int bind_evtchn_to_irq(evtchn_port_t evtchn)
 {
-       return bind_evtchn_to_irq_chip(evtchn, &xen_dynamic_chip, NULL);
+       return bind_evtchn_to_irq_chip(evtchn, &xen_dynamic_chip, NULL, false);
 }
 EXPORT_SYMBOL_GPL(bind_evtchn_to_irq);
 
 int bind_evtchn_to_irq_lateeoi(evtchn_port_t evtchn)
 {
-       return bind_evtchn_to_irq_chip(evtchn, &xen_lateeoi_chip, NULL);
+       return bind_evtchn_to_irq_chip(evtchn, &xen_lateeoi_chip, NULL, false);
 }
 EXPORT_SYMBOL_GPL(bind_evtchn_to_irq_lateeoi);
 
@@ -1295,7 +1296,8 @@ static int bind_ipi_to_irq(unsigned int ipi, unsigned int 
cpu)
 
 static int bind_interdomain_evtchn_to_irq_chip(struct xenbus_device *dev,
                                               evtchn_port_t remote_port,
-                                              struct irq_chip *chip)
+                                              struct irq_chip *chip,
+                                              bool shared)
 {
        struct evtchn_bind_interdomain bind_interdomain;
        int err;
@@ -1307,14 +1309,14 @@ static int bind_interdomain_evtchn_to_irq_chip(struct 
xenbus_device *dev,
                                          &bind_interdomain);
 
        return err ? : bind_evtchn_to_irq_chip(bind_interdomain.local_port,
-                                              chip, dev);
+                                              chip, dev, shared);
 }
 
 int bind_interdomain_evtchn_to_irq_lateeoi(struct xenbus_device *dev,
                                           evtchn_port_t remote_port)
 {
        return bind_interdomain_evtchn_to_irq_chip(dev, remote_port,
-                                                  &xen_lateeoi_chip);
+                                                  &xen_lateeoi_chip, false);
 }
 EXPORT_SYMBOL_GPL(bind_interdomain_evtchn_to_irq_lateeoi);
 
@@ -1430,7 +1432,8 @@ static int bind_evtchn_to_irqhandler_chip(evtchn_port_t 
evtchn,
 {
        int irq, retval;
 
-       irq = bind_evtchn_to_irq_chip(evtchn, chip, NULL);
+       irq = bind_evtchn_to_irq_chip(evtchn, chip, NULL,
+                                     irqflags & IRQF_SHARED);
        if (irq < 0)
                return irq;
        retval = request_irq(irq, handler, irqflags, devname, dev_id);
@@ -1471,7 +1474,8 @@ static int bind_interdomain_evtchn_to_irqhandler_chip(
 {
        int irq, retval;
 
-       irq = bind_interdomain_evtchn_to_irq_chip(dev, remote_port, chip);
+       irq = bind_interdomain_evtchn_to_irq_chip(dev, remote_port, chip,
+                                                 irqflags & IRQF_SHARED);
        if (irq < 0)
                return irq;
 
-- 
2.35.3