From mboxrd@z Thu Jan  1 00:00:00 1970
From: Olaf Hering <olaf@aepfle.de>
Subject: Re: how to prevent crashes in
 notify_via_xen_event_channel during shutdown/crash
Date: Tue, 14 Sep 2010 23:40:39 +0200
Message-ID: <20100914214039.GA12522@aepfle.de>
References: <20100907195207.GA1428@aepfle.de>
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On Tue, Sep 07, Olaf Hering wrote:

> 
> Hello,
> 
> I'm seeing crashes with 4.0.1 in notify_via_xen_event_channel() after
> evtchn_destroy() was already executed, the ASSERT triggers.
> There are a few calls to notify_via_xen_event_channel(), only
> hvm_send_assist_req() seems to check the domain->is_shutting_down flag.
> xen-unstable is not much different in that area.
> 
> How should a check for an already destroyed eventchannel look like?
> Maybe like its done in free_xen_event_channel()?

This patch fixes the crashes for me.


--- xen-4.0.1-testing.orig/xen/common/event_channel.c
+++ xen-4.0.1-testing/xen/common/event_channel.c
@@ -994,6 +994,12 @@ void notify_via_xen_event_channel(struct
 
     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(lchn->consumer_is_xen);