sched_credit: Hold lock while dump scheduler info

Dump runq with debug key 'r' may cause dead loop like below:

(XEN) active vcpus:
(XEN)     1: [1.0] pri=0 flags=0 cpu=0 credit=263 [w=256]
(XEN)     2: [0.2] pri=0 flags=0 cpu=5 credit=284 [w=256]
(XEN)     3: [0.2] pri=0 flags=0 cpu=5 credit=282 [w=256]
...
(XEN)  xxxxx: [0.2] pri=0 flags=0 cpu=2 credit=54 [w=256]
...
(XEN)  xxxxx: [0.2] pri=0 flags=0 cpu=3 credit=-48 [w=256]
...

This means the active vcpu 0.2 became non-active with the active list
element empty just after it was accessed in the loop '2:'.

We should always hold a lock before access scheduler related list,
even in the debug purpose dump code.

Signed-off-by: Wei Gang <gang.wei@intel.com>

xen/common/sched_credit.c

@@ -1452,6 +1452,10 @@ csched_dump(const struct scheduler *ops)
     struct list_head *iter_sdom, *iter_svc;
     struct csched_private *prv = CSCHED_PRIV(ops);
     int loop;
+    unsigned long flags;
+
+    spin_lock_irqsave(&(prv->lock), flags);
+
 #define idlers_buf keyhandler_scratch
 
     printk("info:\n"
@@ -1500,6 +1504,8 @@ csched_dump(const struct scheduler *ops)
         }
     }
 #undef idlers_buf
+
+    spin_unlock_irqrestore(&(prv->lock), flags);
 }
 
 static int