[PATCH 1/2] xen/evtchn: avoid WARN() when unbinding an event channel

[Juergen Gross <jgross@xxxxxxxx>]

When unbinding a user event channel, the related handler might be
called a last time in case the kernel was built with
CONFIG_DEBUG_SHIRQ. This might cause a WARN() in the handler.

Avoid that by adding an "unbinding" flag to struct user_event which
will short circuit the handler.

Fixes: 9e90e58c11b7 ("xen: evtchn: Allow shared registration of IRQ handers")
Reported-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
Tested-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 drivers/xen/evtchn.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c
index 59717628ca42..f6a2216c2c87 100644
--- a/drivers/xen/evtchn.c
+++ b/drivers/xen/evtchn.c
@@ -85,6 +85,7 @@ struct user_evtchn {
        struct per_user_data *user;
        evtchn_port_t port;
        bool enabled;
+       bool unbinding;
 };
 
 static void evtchn_free_ring(evtchn_port_t *ring)
@@ -164,6 +165,10 @@ static irqreturn_t evtchn_interrupt(int irq, void *data)
        struct per_user_data *u = evtchn->user;
        unsigned int prod, cons;
 
+       /* Handler might be called when tearing down the IRQ. */
+       if (evtchn->unbinding)
+               return IRQ_HANDLED;
+
        WARN(!evtchn->enabled,
             "Interrupt for port %u, but apparently not enabled; per-user %p\n",
             evtchn->port, u);
@@ -421,6 +426,7 @@ static void evtchn_unbind_from_user(struct per_user_data *u,
 
        BUG_ON(irq < 0);
 
+       evtchn->unbinding = true;
        unbind_from_irqhandler(irq, evtchn);
 
        del_evtchn(u, evtchn);
-- 
2.35.3