[Qemu-devel] [PULL 40/43] tcg: add memory barriers in page_find_alloc accesses

[Paolo Bonzini <pbonzini@redhat.com>]

page_find is reading the radix tree outside all locks, so it has to
use the RCU primitives.  It does not need RCU critical sections
because the PageDescs are never removed, so there is never a need
to wait for the end of code sections that use a PageDesc.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 translate-all.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/translate-all.c b/translate-all.c
index 37bb56c..5329982 100644
--- a/translate-all.c
+++ b/translate-all.c
@@ -431,26 +431,26 @@ static PageDesc *page_find_alloc(tb_page_addr_t index, int alloc)
 
     /* Level 2..N-1.  */
     for (i = V_L1_SHIFT / V_L2_BITS - 1; i > 0; i--) {
-        void **p = *lp;
+        void **p = atomic_rcu_read(lp);
 
         if (p == NULL) {
             if (!alloc) {
                 return NULL;
             }
             p = g_new0(void *, V_L2_SIZE);
-            *lp = p;
+            atomic_rcu_set(lp, p);
         }
 
         lp = p + ((index >> (i * V_L2_BITS)) & (V_L2_SIZE - 1));
     }
 
-    pd = *lp;
+    pd = atomic_rcu_read(lp);
     if (pd == NULL) {
         if (!alloc) {
             return NULL;
         }
         pd = g_new0(PageDesc, V_L2_SIZE);
-        *lp = pd;
+        atomic_rcu_set(lp, pd);
     }
 
     return pd + (index & (V_L2_SIZE - 1));
-- 
2.4.3