drm/msm: Add priv->mm_lock to protect active/inactive lists

Rather than relying on the big dev->struct_mutex hammer, introduce a
more specific lock for protecting the bo lists.

Change-Id: I4c876a1c3ae51ff62372703a99a8daff0c4a7950
Signed-off-by: Rob Clark <robdclark@chromium.org>
Git-commit: d984457b31c4c53d2af374d5e78b3eb64debd483
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
[samtran@codeaurora.org: avoid changes related to debugfs and shrinker]
Signed-off-by: Samantha Tran <samtran@codeaurora.org>

msm/msm_drv.h

@@ -888,8 +888,19 @@ struct msm_drm_private {
 	struct msm_rd_state *hangrd;   /* debugfs to dump hanging submits */
 	struct msm_perf_state *perf;
 
-	/* list of GEM objects: */
+	/*
+	 * List of inactive GEM objects.  Every bo is either in the inactive_list
+	 * or gpu->active_list (for the gpu it is active on[1])
+	 *
+	 * These lists are protected by mm_lock.  If struct_mutex is involved, it
+	 * should be aquired prior to mm_lock.  One should *not* hold mm_lock in
+	 * get_pages()/vmap()/etc paths, as they can trigger the shrinker.
+	 *
+	 * [1] if someone ever added support for the old 2d cores, there could be
+	 *     more than one gpu object
+	 */
 	struct list_head inactive_list;
+	struct mutex mm_lock;
 
 	/* worker for delayed free of objects: */
 	struct work_struct free_work;