win32u: Use consistent locking order for display related mutexes.

Most paths that hold both the display_lock and the display_devices_init mutex acquire them in the order just mentioned. However, there are two cases where these are acquired in the opposite order, which with unfortunate thread interactions and timings can lead to a deadlock. Fix these cases to use the same order as the rest of the code.

win32u: Use consistent locking order for display related mutexes.
26e3d2ec · Alexandros Frantzis · Alexandre Julliard · c8bf3ba2 · 26e3d2ec
Commit 26e3d2ec authored Feb 06, 2024 by Alexandros Frantzis Committed by Alexandre Julliard Feb 08, 2024
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sysparams.c dlls/win32u/sysparams.c +2 -2

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--- a/dlls/win32u/sysparams.c
+++ b/dlls/win32u/sysparams.c
@@ -1251,8 +1251,8 @@ static void add_gpu( const struct gdi_gpu *gpu, void *param )
    if (!ctx->mutex)
    {
-        ctx->mutex = get_display_device_init_mutex();
        pthread_mutex_lock( &display_lock );
+        ctx->mutex = get_display_device_init_mutex();
        prepare_devices();
    }
@@ -1717,8 +1717,8 @@ static BOOL update_display_cache_from_registry(void)
    if (key.LastWriteTime.QuadPart <= last_query_display_time) return TRUE;
-    mutex = get_display_device_init_mutex();
    pthread_mutex_lock( &display_lock );
+    mutex = get_display_device_init_mutex();
    clear_display_devices();