From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <JBeulich@novell.com>
Subject: Re: [RFC][PATCH] walking the page lists needs the
	page_alloc lock
Date: Fri, 13 Aug 2010 08:20:00 +0100
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	<C88AAE59.1D986%keir.fraser@eu.citrix.com>
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To: Keir Fraser <keir.fraser@eu.citrix.com>
Cc: Tim Deegan <Tim.Deegan@eu.citrix.com>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
List-Id: xen-devel@lists.xenproject.org

>>> On 13.08.10 at 09:10, Keir Fraser <keir.fraser@eu.citrix.com> wrote:
> On 13/08/2010 08:06, "Jan Beulich" <JBeulich@novell.com> wrote:
>=20
>>>> But then, to avoid a hanging system, these should be trylock-s
>>>> rather than plain locks, shouldn't they?
>>>=20
>>> Why? The handler is called in softirq context. It should be safe to =
spin.
>>=20
>> Hmm, indeed. I was looking at others, and at least
>> domain_dump_evtchn_info() also uses a trylock - apparently for
>> no good reason.
>=20
> Well, since you wrote that function, would you like me to switch
> domain_dump_evtchn_info() to do a proper spin_lock()?

Yes. I'd want to do a little cleanup to the initial printk()-s at once,
like in the patch below.

Jan

Signed-off-by: Jan Beulich <jbeulich@novell.com>

--- 2010-08-12.orig/xen/common/event_channel.c
+++ 2010-08-12/xen/common/event_channel.c
@@ -1123,14 +1123,11 @@ static void domain_dump_evtchn_info(stru
=20
     bitmap_scnlistprintf(keyhandler_scratch, sizeof(keyhandler_scratch),
                          d->poll_mask, d->max_vcpus);
-    printk("Domain %d polling vCPUs: {%s}\n",
-           d->domain_id, keyhandler_scratch);
-
-    if ( !spin_trylock(&d->event_lock) )
-        return;
-
     printk("Event channel information for domain %d:\n"
-           "    port [p/m]\n", d->domain_id);
+           "Polling vCPUs: {%s}\n"
+           "    port [p/m]\n", d->domain_id, keyhandler_scratch);
+
+    spin_lock(&d->event_lock);
=20
     for ( port =3D 1; port < MAX_EVTCHNS(d); ++port )
     {