[Qemu-devel] [PULL 14/21] migration: use bitmap_mutex in migration_bitmap_clear_dirty

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: Wei Wang <wei.w.wang@intel.com>

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>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <1544516693-5395-4-git-send-email-wei.w.wang@intel.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 migration/ram.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/migration/ram.c b/migration/ram.c
index 01315edd66..0747873ca9 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -342,7 +342,7 @@ struct RAMState {
     uint64_t target_page_count;
     /* number of dirty bits in the bitmap */
     uint64_t migration_dirty_pages;
-    /* protects modification of the bitmap */
+    /* Protects modification of the bitmap and migration dirty pages */
     QemuMutex bitmap_mutex;
     /* The RAMBlock used in the last src_page_requests */
     RAMBlock *last_req_rb;
@@ -1590,11 +1590,14 @@ 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;
 }
 
-- 
2.20.1