[Xen-changelog] [xen-unstable] Avoid endless loop for vcpu migration.

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
# Date 1300184067 0
# Node ID 3caed2112c65791855e8bf0fd34c15e3160bbc78
# Parent  599ceb5b0a9b014cf609e4c9e54c54c51b3217e5
Avoid endless loop for vcpu migration.

Only call SCHED_OP(pick_cpu) if a previously picked cpu is not
suitable on the current iteration of the retry loop.

Signed-off-by: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
Signed-off-by: Keir Fraser <keir@xxxxxxx>
---


diff -r 599ceb5b0a9b -r 3caed2112c65 xen/common/schedule.c
--- a/xen/common/schedule.c     Tue Mar 15 10:02:36 2011 +0000
+++ b/xen/common/schedule.c     Tue Mar 15 10:14:27 2011 +0000
@@ -395,6 +395,7 @@
     unsigned long flags;
     unsigned int old_cpu, new_cpu;
     spinlock_t *old_lock, *new_lock;
+    bool_t pick_called = 0;
 
     old_cpu = new_cpu = v->processor;
     for ( ; ; )
@@ -426,14 +427,33 @@
             spin_lock(old_lock);
         }
 
-        /* Select new CPU. */
         old_cpu = v->processor;
         if ( old_lock == per_cpu(schedule_data, old_cpu).schedule_lock )
         {
+            /*
+             * If we selected a CPU on the previosu iteration, check if it
+             * remains suitable for running this vCPU.
+             */
+            if ( pick_called &&
+                 (new_lock == per_cpu(schedule_data, new_cpu).schedule_lock) &&
+                 cpu_isset(new_cpu, v->cpu_affinity) &&
+                 cpu_isset(new_cpu, v->domain->cpupool->cpu_valid) )
+                break;
+
+            /* Select a new CPU. */
             new_cpu = SCHED_OP(VCPU2OP(v), pick_cpu, v);
             if ( (new_lock == per_cpu(schedule_data, new_cpu).schedule_lock) &&
                  cpu_isset(new_cpu, v->domain->cpupool->cpu_valid) )
                 break;
+            pick_called = 1;
+        }
+        else
+        {
+            /*
+             * We do not hold the scheduler lock appropriate for this vCPU.
+             * Thus we cannot select a new CPU on this iteration. Try again.
+             */
+            pick_called = 0;
         }
 
         if ( old_lock != new_lock )

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