[Xen-changelog] [xen-3.4-testing] PoD: Handle operations properly when domain is dying

["Xen patchbot-3.4-testing" <patchbot-3.4-testing@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1259310161 0
# Node ID 8c5708bc87adb3ae7dd5f0ccc7a84bb57f7ca8f4
# Parent  455c6392747f8a4801b2dcced1265ad4cc9086fe
PoD: Handle operations properly when domain is dying

No populate-on-demand activities should happen when a domain is dying.
Especially, it is a bug for memory to be added to the PoD cache when
d->is_dying is non-zero, since if this happens after the cache has
been emptied, these pages will never be freed. This may cause "zombie
domains" to linger.

Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
xen-unstable changeset:   20426:368cfc61e7b6
xen-unstable date:        Thu Nov 12 11:39:51 2009 +0000
---
 xen/arch/x86/mm/p2m.c |   15 ++++++++++++++-
 1 files changed, 14 insertions(+), 1 deletion(-)

diff -r 455c6392747f -r 8c5708bc87ad xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c     Tue Nov 10 15:04:00 2009 +0000
+++ b/xen/arch/x86/mm/p2m.c     Fri Nov 27 08:22:41 2009 +0000
@@ -292,6 +292,8 @@ p2m_pod_cache_add(struct domain *d,
     default:
         BUG();
     }
+
+    BUG_ON(d->is_dying);
 
     spin_unlock(&d->page_alloc_lock);
 
@@ -493,6 +495,10 @@ p2m_pod_set_mem_target(struct domain *d,
     if ( p2md->pod.entry_count == 0 )
         goto out;
 
+    /* Don't do anything if the domain is being torn down */
+    if ( d->is_dying )
+        goto out;
+
     /* T' < B: Don't reduce the cache size; let the balloon driver
      * take care of it. */
     if ( target < d->tot_pages )
@@ -572,7 +578,7 @@ p2m_pod_decrease_reservation(struct doma
 
     /* If we don't have any outstanding PoD entries, let things take their
      * course */
-    if ( p2md->pod.entry_count == 0 )
+    if ( p2md->pod.entry_count == 0 || unlikely(d->is_dying) )
         goto out;
 
     /* Figure out if we need to steal some freed memory for our cache */
@@ -1008,6 +1014,12 @@ p2m_pod_demand_populate(struct domain *d
         return 0;
     }
 
+    /* This check is done with the p2m lock held.  This will make sure that
+     * even if d->is_dying changes under our feet, empty_pod_cache() won't 
start
+     * until we're done. */
+    if ( unlikely(d->is_dying) )
+        goto out_fail;
+
     /* If we're low, start a sweep */
     if ( order == 9 && page_list_empty(&p2md->pod.super) )
         p2m_pod_emergency_sweep_super(d);
@@ -1077,6 +1089,7 @@ out_of_memory:
     p2m_unlock(p2md);
     printk("%s: Out of populate-on-demand memory!\n", __func__);
     domain_crash(d);
+out_fail:
     return -1;
 remap_and_retry:
     BUG_ON(order != 9);

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