[Xen-changelog] [xen-4.0-testing] Walking the page lists needs the page_alloc lock

["Xen patchbot-4.0-testing" <patchbot-4.0-testing@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1280765493 -3600
# Node ID b782ca7d09e8b20723ca11082173e255a38bbd39
# Parent  a3025308b7906286e1f63b1e66d391096a0c236a
Walking the page lists needs the page_alloc lock

There are a few places in Xen where we walk a domain's page lists
without holding the page_alloc lock.  They race with updates to the
page lists, which are normally rare but can be quite common under PoD
when the domain is close to its memory limit and the PoD reclaimer is
busy.  This patch protects those places by taking the page_alloc lock.

I think this is OK for the two debug-key printouts - they don't run
from irq context and look deadlock-free.  The tboot change seems safe
too unless tboot shutdown functions are called from irq context or
with the page_alloc lock held.  The p2m one is the scariest but there
are already code paths in PoD that take the page_alloc lock with the
p2m lock held so it's no worse than existing code.

Signed-off-by: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
xen-unstable changeset:   21881:57de3a3118bb
xen-unstable date:        Wed Jul 28 07:54:12 2010 +0100
---
 xen/arch/x86/domain.c |    4 ++++
 xen/arch/x86/mm/p2m.c |    8 ++++++--
 xen/arch/x86/numa.c   |    2 ++
 xen/arch/x86/tboot.c  |    2 ++
 4 files changed, 14 insertions(+), 2 deletions(-)

diff -r a3025308b790 -r b782ca7d09e8 xen/arch/x86/domain.c
--- a/xen/arch/x86/domain.c     Mon Aug 02 17:10:32 2010 +0100
+++ b/xen/arch/x86/domain.c     Mon Aug 02 17:11:33 2010 +0100
@@ -150,12 +150,14 @@ void dump_pageframe_info(struct domain *
     }
     else
     {
+        spin_lock(&d->page_alloc_lock);
         page_list_for_each ( page, &d->page_list )
         {
             printk("    DomPage %p: caf=%08lx, taf=%" PRtype_info "\n",
                    _p(page_to_mfn(page)),
                    page->count_info, page->u.inuse.type_info);
         }
+        spin_unlock(&d->page_alloc_lock);
     }
 
     if ( is_hvm_domain(d) )
@@ -163,12 +165,14 @@ void dump_pageframe_info(struct domain *
         p2m_pod_dump_data(d);
     }
 
+    spin_lock(&d->page_alloc_lock);
     page_list_for_each ( page, &d->xenpage_list )
     {
         printk("    XenPage %p: caf=%08lx, taf=%" PRtype_info "\n",
                _p(page_to_mfn(page)),
                page->count_info, page->u.inuse.type_info);
     }
+    spin_unlock(&d->page_alloc_lock);
 }
 
 struct domain *alloc_domain_struct(void)
diff -r a3025308b790 -r b782ca7d09e8 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c     Mon Aug 02 17:10:32 2010 +0100
+++ b/xen/arch/x86/mm/p2m.c     Mon Aug 02 17:11:33 2010 +0100
@@ -1674,6 +1674,7 @@ int p2m_alloc_table(struct domain *d,
         goto error;
 
     /* Copy all existing mappings from the page list and m2p */
+    spin_lock(&d->page_alloc_lock);
     page_list_for_each(page, &d->page_list)
     {
         mfn = page_to_mfn(page);
@@ -1689,13 +1690,16 @@ int p2m_alloc_table(struct domain *d,
 #endif
              && gfn != INVALID_M2P_ENTRY
             && !set_p2m_entry(d, gfn, mfn, 0, p2m_ram_rw) )
-            goto error;
-    }
+            goto error_unlock;
+    }
+    spin_unlock(&d->page_alloc_lock);
 
     P2M_PRINTK("p2m table initialised (%u pages)\n", page_count);
     p2m_unlock(p2m);
     return 0;
 
+error_unlock:
+    spin_unlock(&d->page_alloc_lock);
  error:
     P2M_PRINTK("failed to initialize p2m table, gfn=%05lx, mfn=%"
                PRI_mfn "\n", gfn, mfn_x(mfn));
diff -r a3025308b790 -r b782ca7d09e8 xen/arch/x86/numa.c
--- a/xen/arch/x86/numa.c       Mon Aug 02 17:10:32 2010 +0100
+++ b/xen/arch/x86/numa.c       Mon Aug 02 17:11:33 2010 +0100
@@ -380,11 +380,13 @@ static void dump_numa(unsigned char key)
                for_each_online_node(i)
                        page_num_node[i] = 0;
 
+               spin_lock(&d->page_alloc_lock);
                page_list_for_each(page, &d->page_list)
                {
                        i = phys_to_nid((paddr_t)page_to_mfn(page) << 
PAGE_SHIFT);
                        page_num_node[i]++;
                }
+               spin_unlock(&d->page_alloc_lock);
 
                for_each_online_node(i)
                        printk("    Node %u: %u\n", i, page_num_node[i]);
diff -r a3025308b790 -r b782ca7d09e8 xen/arch/x86/tboot.c
--- a/xen/arch/x86/tboot.c      Mon Aug 02 17:10:32 2010 +0100
+++ b/xen/arch/x86/tboot.c      Mon Aug 02 17:11:33 2010 +0100
@@ -211,12 +211,14 @@ static void tboot_gen_domain_integrity(c
             continue;
         printk("MACing Domain %u\n", d->domain_id);
 
+        spin_lock(&d->page_alloc_lock);
         page_list_for_each(page, &d->page_list)
         {
             void *pg = __map_domain_page(page);
             vmac_update(pg, PAGE_SIZE, &ctx);
             unmap_domain_page(pg);
         }
+        spin_unlock(&d->page_alloc_lock);
 
         if ( !is_idle_domain(d) )
         {

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