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

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1258025991 0
# Node ID 368cfc61e7b6993bb599ebf7b0bafb78d245852b
# Parent  01a941f2c9f5d7ab73436b44977695a9e4ea0060
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/arch/x86/mm/p2m.c |   15 ++++++++++++++-
 1 files changed, 14 insertions(+), 1 deletion(-)

diff -r 01a941f2c9f5 -r 368cfc61e7b6 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c     Wed Nov 11 13:11:44 2009 +0000
+++ b/xen/arch/x86/mm/p2m.c     Thu Nov 12 11:39:51 2009 +0000
@@ -302,6 +302,8 @@ p2m_pod_cache_add(struct domain *d,
     default:
         BUG();
     }
+
+    BUG_ON(d->is_dying);
 
     spin_unlock(&d->page_alloc_lock);
 
@@ -503,6 +505,10 @@ 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 )
@@ -582,7 +588,7 @@ 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 */
@@ -1002,6 +1008,12 @@ p2m_pod_demand_populate(struct domain *d
     struct p2m_domain *p2md = d->arch.p2m;
     int i;
 
+    /* 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);
@@ -1048,6 +1060,7 @@ out_of_memory:
     printk("%s: Out of populate-on-demand memory! tot_pages %" PRIu32 " 
pod_entries %" PRIi32 "\n",
            __func__, d->tot_pages, p2md->pod.entry_count);
     domain_crash(d);
+out_fail:
     return -1;
 remap_and_retry:
     BUG_ON(order != 9);

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