[Qemu-devel] [PATCH v2 2/4] exec: Atomic access to map_client_list

[Fam Zheng <famz@redhat.com>]

Change map_client_list to QSLIST which supports atomic operations.

There are two access points to map_client_list. One is
cpu_register_map_client, the other is cpu_notify_map_clients called
after releasing the global bounce buffer in address_space_unmap. Each
is now converted to a single atomic operation.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 exec.c | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/exec.c b/exec.c
index 8d4e134..93ccd5a 100644
--- a/exec.c
+++ b/exec.c
@@ -2489,11 +2489,11 @@ static BounceBuffer bounce;
 typedef struct MapClient {
     void *opaque;
     void (*callback)(void *opaque);
-    QLIST_ENTRY(MapClient) link;
+    QSLIST_ENTRY(MapClient) link;
 } MapClient;
 
-static QLIST_HEAD(map_client_list, MapClient) map_client_list
-    = QLIST_HEAD_INITIALIZER(map_client_list);
+static QSLIST_HEAD(map_client_list, MapClient) map_client_list
+    = QSLIST_HEAD_INITIALIZER(map_client_list);
 
 void *cpu_register_map_client(void *opaque, void (*callback)(void *opaque))
 {
@@ -2501,26 +2501,23 @@ void *cpu_register_map_client(void *opaque, void (*callback)(void *opaque))
 
     client->opaque = opaque;
     client->callback = callback;
-    QLIST_INSERT_HEAD(&map_client_list, client, link);
+    QSLIST_INSERT_HEAD_ATOMIC(&map_client_list, client, link);
     return client;
 }
 
-static void cpu_unregister_map_client(void *_client)
-{
-    MapClient *client = (MapClient *)_client;
-
-    QLIST_REMOVE(client, link);
-    g_free(client);
-}
-
 static void cpu_notify_map_clients(void)
 {
     MapClient *client;
+    QSLIST_HEAD(, MapClient) mclist;
 
-    while (!QLIST_EMPTY(&map_client_list)) {
-        client = QLIST_FIRST(&map_client_list);
+    /* Only the bounce buffer owner thread could possibly call this, but we
+     * should also coordinate with cpu_register_map_client. */
+    QSLIST_MOVE_ATOMIC(&mclist, &map_client_list);
+    while (!QSLIST_EMPTY(&mclist)) {
+        client = QSLIST_FIRST(&mclist);
         client->callback(client->opaque);
-        cpu_unregister_map_client(client);
+        QSLIST_REMOVE_HEAD(&mclist, link);
+        g_free(client);
     }
 }
 
-- 
1.9.3