drm/msm/gem: Protect pin_count/madv by LRU lock

Since the LRU lock is already acquired when moving an obj between LRUs,
we can use it to protect pin_count and madv, without any significant
change in locking (ie. it just expands the scope of the lock by a hand-
ful of instructions).  This prepares the way to decrement the pin_count
in the job_run() path without needing to hold the obj lock, to avoid a
potential deadlock (or rather stall) caused by the fence-signaling path
(job_run()) blocking on shrinker/reclaim.  (Only a stall because the
wait for fence signaling wait_for_idle() is not infinite.)

Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/527843/
Link: https://lore.kernel.org/r/20230320144356.803762-9-robdclark@gmail.com

1 files changed, 8 insertions, 1 deletions

diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
index 1929f09c5b0d..0057e8e8fa13 100644
--- a/drivers/gpu/drm/msm/msm_gem.h
+++ b/drivers/gpu/drm/msm/msm_gem.h
@@ -86,7 +86,9 @@ struct msm_gem_object {
 	uint32_t flags;
 
 	/**
-	 * Advice: are the backing pages purgeable?
+	 * madv: are the backing pages purgeable?
+	 *
+	 * Protected by obj lock and LRU lock
 	 */
 	uint8_t madv;
 
@@ -114,6 +116,11 @@ struct msm_gem_object {
 
 	char name[32]; /* Identifier to print for the debugfs files */
 
+	/**
+	 * pin_count: Number of times the pages are pinned
+	 *
+	 * Protected by LRU lock.
+	 */
 	int pin_count;
 };
 #define to_msm_bo(x) container_of(x, struct msm_gem_object, base)