drm/qxl: Call qxl_bo_unref outside atomic context

"qxl_bo_unref" may sleep, but calling "qxl_release_map" causes
"preempt_disable()" to be called and "preempt_enable()" isn't called
until "qxl_release_unmap" is used. Move the call to "qxl_bo_unref" out
from in between the two to avoid sleeping from an atomic context.

This issue can be demonstrated on a kernel with CONFIG_LOCKDEP=y by
creating a VM using QXL, using a desktop environment using Xorg, then
moving the cursor on or off a window.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1571128
Fixes: 9428088c90b6 ("drm/qxl: reapply cursor after resetting primary")
Cc: stable@vger.kernel.org
Signed-off-by: Jeremy Cline <jcline@redhat.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20180601200532.13619-1-jcline@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/gpu/drm/qxl/qxl_display.c b/drivers/gpu/drm/qxl/qxl_display.c
index ecb35ed0eac8..61e51516fec5 100644
--- a/drivers/gpu/drm/qxl/qxl_display.c
+++ b/drivers/gpu/drm/qxl/qxl_display.c
@@ -630,7 +630,7 @@ static void qxl_cursor_atomic_update(struct drm_plane *plane,
         struct qxl_cursor_cmd *cmd;
         struct qxl_cursor *cursor;
         struct drm_gem_object *obj;
-        struct qxl_bo *cursor_bo = NULL, *user_bo = NULL;
+        struct qxl_bo *cursor_bo = NULL, *user_bo = NULL, *old_cursor_bo = NULL;
         int ret;
         void *user_ptr;
         int size = 64*64*4;
@@ -684,7 +684,7 @@ static void qxl_cursor_atomic_update(struct drm_plane *plane,
                                                            cursor_bo, 0);
                 cmd->type = QXL_CURSOR_SET;
 
-                qxl_bo_unref(&qcrtc->cursor_bo);
+                old_cursor_bo = qcrtc->cursor_bo;
                 qcrtc->cursor_bo = cursor_bo;
                 cursor_bo = NULL;
         } else {
@@ -704,6 +704,9 @@ static void qxl_cursor_atomic_update(struct drm_plane *plane,
         qxl_push_cursor_ring_release(qdev, release, QXL_CMD_CURSOR, false);
         qxl_release_fence_buffer_objects(release);
 
+        if (old_cursor_bo)
+                qxl_bo_unref(&old_cursor_bo);
+
         qxl_bo_unref(&cursor_bo);
 
         return;