[Xen-devel] [PATCH 2/4] x86/IRQ: bail early from irq_guest_eoi_timer_fn() when nothing is in flight

["Jan Beulich" <JBeulich@xxxxxxxx>]

There's no point entering the loop in the function in this case. Instead
there still being something in flight _after_ the loop would be an
actual problem: No timer would be running anymore for issuing the EOI
eventually, and hence this IRQ (and possibly lower priority ones) would
be blocked, perhaps indefinitely.

Issue a warning instead and prefer breaking some (presumably
misbehaving) guest over stalling perhaps the entire system.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -1115,7 +1115,7 @@ static void irq_guest_eoi_timer_fn(void
 
     action = (irq_guest_action_t *)desc->action;
 
-    if ( timer_is_active(&action->eoi_timer) )
+    if ( !action->in_flight || timer_is_active(&action->eoi_timer) )
         goto out;
 
     if ( action->ack_type != ACKTYPE_NONE )
@@ -1130,8 +1130,10 @@ static void irq_guest_eoi_timer_fn(void
         }
     }
 
-    if ( action->in_flight != 0 )
-        goto out;
+    if ( action->in_flight )
+        printk(XENLOG_G_WARNING
+               "IRQ%d: %d handlers still in flight at forced EOI\n",
+               desc->irq, action->in_flight);
 
     switch ( action->ack_type )
     {





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