[Xen-devel] [PATCHv4 2/4] evtchn: defer freeing struct evtchn's until evtchn_destroy_final()

[David Vrabel <david.vrabel@xxxxxxxxxx>]

notify_via_xen_event_channel() and free_xen_event_channel() had to
check if the domain was dying because they may be called while the
domain is being destroyed and the struct evtchn's are being freed.

By deferring the freeing of the struct evtchn's until all references
to the domain are dropped, these functions can rely on the channel
state being present and valid.

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
v4:
- Re-add BUG_ON(!port_is_valid()).
---
 xen/common/event_channel.c |   46 ++++++++++++--------------------------------
 1 file changed, 12 insertions(+), 34 deletions(-)

diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
index 26870b6..4ee65e6 100644
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -1173,21 +1173,7 @@ int alloc_unbound_xen_event_channel(
 
 void free_xen_event_channel(struct domain *d, int port)
 {
-    struct evtchn *chn;
-
-    spin_lock(&d->event_lock);
-
-    if ( unlikely(d->is_dying) )
-    {
-        spin_unlock(&d->event_lock);
-        return;
-    }
-
     BUG_ON(!port_is_valid(d, port));
-    chn = evtchn_from_port(d, port);
-    BUG_ON(!consumer_is_xen(chn));
-
-    spin_unlock(&d->event_lock);
 
     (void)__evtchn_close(d, port, 0);
 }
@@ -1200,18 +1186,12 @@ void notify_via_xen_event_channel(struct domain *ld, 
int lport)
 
     spin_lock(&ld->event_lock);
 
-    if ( unlikely(ld->is_dying) )
-    {
-        spin_unlock(&ld->event_lock);
-        return;
-    }
-
     ASSERT(port_is_valid(ld, lport));
     lchn = evtchn_from_port(ld, lport);
-    ASSERT(consumer_is_xen(lchn));
 
     if ( likely(lchn->state == ECS_INTERDOMAIN) )
     {
+        ASSERT(consumer_is_xen(lchn));
         rd    = lchn->u.interdomain.remote_dom;
         rchn  = evtchn_from_port(rd, lchn->u.interdomain.remote_port);
         evtchn_port_set_pending(rd, rchn->notify_vcpu_id, rchn);
@@ -1278,7 +1258,7 @@ int evtchn_init(struct domain *d)
 
 void evtchn_destroy(struct domain *d)
 {
-    unsigned int i, j;
+    unsigned int i;
 
     /* After this barrier no new event-channel allocations can occur. */
     BUG_ON(!d->is_dying);
@@ -1288,8 +1268,17 @@ void evtchn_destroy(struct domain *d)
     for ( i = 0; port_is_valid(d, i); i++ )
         (void)__evtchn_close(d, i, 0);
 
+    clear_global_virq_handlers(d);
+
+    evtchn_fifo_destroy(d);
+}
+
+
+void evtchn_destroy_final(struct domain *d)
+{
+    unsigned int i, j;
+
     /* Free all event-channel buckets. */
-    spin_lock(&d->event_lock);
     for ( i = 0; i < NR_EVTCHN_GROUPS; i++ )
     {
         if ( !d->evtchn_group[i] )
@@ -1297,20 +1286,9 @@ void evtchn_destroy(struct domain *d)
         for ( j = 0; j < BUCKETS_PER_GROUP; j++ )
             free_evtchn_bucket(d, d->evtchn_group[i][j]);
         xfree(d->evtchn_group[i]);
-        d->evtchn_group[i] = NULL;
     }
     free_evtchn_bucket(d, d->evtchn);
-    d->evtchn = NULL;
-    spin_unlock(&d->event_lock);
-
-    clear_global_virq_handlers(d);
 
-    evtchn_fifo_destroy(d);
-}
-
-
-void evtchn_destroy_final(struct domain *d)
-{
 #if MAX_VIRT_CPUS > BITS_PER_LONG
     xfree(d->poll_mask);
     d->poll_mask = NULL;
-- 
1.7.10.4


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