svga: init svga_screen::swc_mutex with mtx_recursive

If the SVGA3D_BindGBSurface() call in svga_buffer_hw_storage_unmap()
fails, we'll flush and that might involve unmapping other buffers.
That leads to a recursive lock on svga_screen::swc_mutex and causes
a deadlock.  Fix this by initializing the mutex with mtx_recursive.

Note that this only happened on Linux, not Windows.  On Windows, the
mutex functions are implemented with Win32 critical sections which
support recursive locking.

Also add a comment about this.

Fixes VMware bug 1831549 (Unigine Tropics demo freeze on Linux).

Reviewed-by: Thomas Hellstrom <[email protected]>
Reviewed-by: Neha Bhende<[email protected]>

2 files changed, 4 insertions, 1 deletions

diff --git a/src/gallium/drivers/svga/svga_resource_buffer.c b/src/gallium/drivers/svga/svga_resource_buffer.c
index 7808903083b..271d0787abb 100644
--- a/src/gallium/drivers/svga/svga_resource_buffer.c
+++ b/src/gallium/drivers/svga/svga_resource_buffer.c
@@ -320,6 +320,9 @@ svga_buffer_transfer_unmap( struct pipe_context *pipe,
    }
 
    if (svga_buffer_has_hw_storage(sbuf)) {
+      /* Note: we may wind up flushing here and unmapping other buffers
+       * which leads to recursively locking ss->swc_mutex.
+       */
       svga_buffer_hw_storage_unmap(svga, sbuf);
    }
 
diff --git a/src/gallium/drivers/svga/svga_screen.c b/src/gallium/drivers/svga/svga_screen.c
index 95132fbeb82..74e5485c0ef 100644
--- a/src/gallium/drivers/svga/svga_screen.c
+++ b/src/gallium/drivers/svga/svga_screen.c
@@ -1157,7 +1157,7 @@ svga_screen_create(struct svga_winsys_screen *sws)
    }
 
    (void) mtx_init(&svgascreen->tex_mutex, mtx_plain);
-   (void) mtx_init(&svgascreen->swc_mutex, mtx_plain);
+   (void) mtx_init(&svgascreen->swc_mutex, mtx_recursive);
 
    svga_screen_cache_init(svgascreen);