[PATCH v2 4/8] evtchn: let evtchn_set_priority() acquire the per-channel lock

[Jan Beulich <jbeulich@xxxxxxxx>]

Some lock wants to be held to make sure the port doesn't change state,
but there's no point holding the per-domain event lock here. Switch to
using the finer grained per-channel lock instead.

FAOD this doesn't guarantee anything towards in particular
evtchn_fifo_set_pending(), as for interdomain channels that function
would be called with the remote side's per-channel lock held.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Drop acquiring of event lock. Re-write title and description.

--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -1154,20 +1154,17 @@ static long evtchn_set_priority(const st
 {
     struct domain *d = current->domain;
     unsigned int port = set_priority->port;
+    struct evtchn *chn;
     long ret;
-
-    spin_lock(&d->event_lock);
+    unsigned long flags;
 
     if ( !port_is_valid(d, port) )
-    {
-        spin_unlock(&d->event_lock);
         return -EINVAL;
-    }
-
-    ret = evtchn_port_set_priority(d, evtchn_from_port(d, port),
-                                   set_priority->priority);
 
-    spin_unlock(&d->event_lock);
+    chn = evtchn_from_port(d, port);
+    spin_lock_irqsave(&chn->lock, flags);
+    ret = evtchn_port_set_priority(d, chn, set_priority->priority);
+    spin_unlock_irqrestore(&chn->lock, flags);
 
     return ret;
 }