RE: [Xen-devel] Biweekly VMX status report. Xen: #21438 & Xen0: #a3e7c7...

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

For issue 2, CPU panic when running cpu offline, it should comes from the 
periodic_timer.

When a CPU is pull down, cpu_disable_scheduler will remove the single shot 
timer, but the periodic_timer is not migrated.
After the vcpu is scheduled on another pCPU later, and then schedule out from 
that new pcpu, the stop_timer(&prev->periodic_timer) will try to access the 
per_cpu strucutre, whic still poiting to the offlined CPU's per_cpu area and 
will cause trouble. This should be caused by the per_cpu changes.

I try to migrate the periodic_timer also when cpu_disable_scheduler() and seems 
it works. （comments the migration in cpu_disable_scheudler will trigger the 
printk).
Seems on your side, the timer will always be triggered before schedule out?

--jyh

diff -r 96917cf25bf3 xen/common/schedule.c
--- a/xen/common/schedule.c     Fri May 28 10:54:07 2010 +0100
+++ b/xen/common/schedule.c     Tue Jun 01 15:35:21 2010 +0800
@@ -487,6 +487,15 @@ int cpu_disable_scheduler(unsigned int c
                 migrate_timer(&v->singleshot_timer, cpu_mig);
             }
 
+/*
+            if ( v->periodic_timer.cpu == cpu )
+            {
+                int cpu_mig = first_cpu(c->cpu_valid);
+                if ( cpu_mig == cpu )
+                    cpu_mig = next_cpu(cpu_mig, c->cpu_valid);
+                migrate_timer(&v->periodic_timer, cpu_mig);
+            }
+*/
             if ( v->processor == cpu )
             {
                 set_bit(_VPF_migrating, &v->pause_flags);
@@ -505,7 +514,10 @@ int cpu_disable_scheduler(unsigned int c
              * all locks.
              */
             if ( v->processor == cpu )
+            {
+                printk("we hit the EAGAIN here\n");
                 ret = -EAGAIN;
+            }
         }
     }
     return ret;
@@ -1005,6 +1017,11 @@ static void schedule(void)
 
     perfc_incr(sched_ctx);
 
+    if (prev->periodic_timer.cpu != smp_processor_id() && 
!cpu_online(prev->periodic_timer.cpu))
+    {
+        printk("I'm now at cpu %x, timer's cpu is %x\n", smp_processor_id(), 
prev->periodic_timer.cpu);
+    }
+
     stop_timer(&prev->periodic_timer);
 
     /* Ensure that the domain has an up-to-date time base. */



--jyh

>-----Original Message-----
>From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
>[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Keir Fraser
>Sent: Tuesday, May 25, 2010 5:15 PM
>To: Xu, Jiajun; xen-devel@xxxxxxxxxxxxxxxxxxx
>Subject: Re: [Xen-devel] Biweekly VMX status report. Xen: #21438 & Xen0:
>#a3e7c7...
>
>On 25/05/2010 10:13, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote:
>
>>>>> 1. xen hypervisor hang when create guest on 32e platform
>>>>> http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1617
>>>
>>> The bug occurs each time when I created the guest. I have attached the 
>>> serial
>>> output on the bugzilla.
>>
>> I haven't been able to reproduce this.
>>
>>>>> 2. CPU panic when running cpu offline
>>>>> http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1616
>>>
>>> Xen will panic when I offline cpu each time. The log is also attached on the
>>> bugzilla.
>>
>> Nor this. I even installed 32-bit Xen to match your environment more
>> closely.
>
>I'm running xen-unstable:21447 by the way. I ran 64-bit Xen for testing (1)
>above, and both 64-bit and 32-bit Xen for testing (2).
>
> K.
>
>
>
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