The bitmap mutex is used to synchronize threads to update the dirty
bitmap and the migration_dirty_pages counter. For example, the free
page optimization clears bits of free pages from the bitmap in an
iothread context. This patch makes migration_bitmap_clear_dirty update
the bitmap and counter under the mutex.

Signed-off-by: Wei Wang <wei.w.wang@intel.com>
CC: Dr. David Alan Gilbert <dgilbert@redhat.com>
CC: Juan Quintela <quintela@redhat.com>
CC: Michael S. Tsirkin <mst@redhat.com>
CC: Peter Xu <peterx@redhat.com>
---
 migration/ram.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/migration/ram.c b/migration/ram.c
index c53e836..2eabbe9 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1093,11 +1093,14 @@ static inline bool migration_bitmap_clear_dirty(RAMState *rs,
 {
     bool ret;
 
+    qemu_mutex_lock(&rs->bitmap_mutex);
     ret = test_and_clear_bit(page, rb->bmap);
 
     if (ret) {
         rs->migration_dirty_pages--;
     }
+    qemu_mutex_unlock(&rs->bitmap_mutex);
+
     return ret;
 }
 
-- 
1.8.3.1