linux-kernel - [PATCH] drm/ttm: Remove pinned bos from LRU in ttm_bo_move_to_lru

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Date:   Mon,  4 Jan 2021 18:13:58 -0500
From:   Lyude Paul <lyude@...hat.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     Christian König <christian.koenig@....com>,
        Dave Airlie <airlied@...hat.com>,
        Huang Rui <ray.huang@....com>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Andrey Grodzovsky <andrey.grodzovsky@....com>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] drm/ttm: Remove pinned bos from LRU in ttm_bo_move_to_lru_tail()

Recently a regression was introduced which caused TTM's buffer eviction to
attempt to evict already-pinned BOs, causing issues with buffer eviction
under memory pressure along with suspend/resume:

  nouveau 0000:1f:00.0: DRM: evicting buffers...
  nouveau 0000:1f:00.0: DRM: Moving pinned object 00000000c428c3ff!
  nouveau 0000:1f:00.0: fifo: fault 00 [READ] at 0000000000200000 engine 04
  [BAR1] client 07 [HUB/HOST_CPU] reason 02 [PTE] on channel -1 [00ffeaa000
  unknown]
  nouveau 0000:1f:00.0: fifo: DROPPED_MMU_FAULT 00001000
  nouveau 0000:1f:00.0: fifo: fault 01 [WRITE] at 0000000000020000 engine
  0c [HOST6] client 07 [HUB/HOST_CPU] reason 02 [PTE] on channel 1
  [00ffb28000 DRM]
  nouveau 0000:1f:00.0: fifo: channel 1: killed
  nouveau 0000:1f:00.0: fifo: runlist 0: scheduled for recovery
  [TTM] Buffer eviction failed
  nouveau 0000:1f:00.0: DRM: waiting for kernel channels to go idle...
  nouveau 0000:1f:00.0: DRM: failed to idle channel 1 [DRM]
  nouveau 0000:1f:00.0: DRM: resuming display...

After some bisection and investigation, it appears this resulted from the
recent changes to ttm_bo_move_to_lru_tail(). Previously when a buffer was
pinned, the buffer would be removed from the LRU once ttm_bo_unreserve
to maintain the LRU list when pinning or unpinning BOs. However, since:

commit 3d1a88e1051f ("drm/ttm: cleanup LRU handling further")

We've been exiting from ttm_bo_move_to_lru_tail() at the very beginning of
the function if the bo we're looking at is pinned, resulting in the pinned
BO never getting removed from the lru and as a result - causing issues when
it eventually becomes time for eviction.

So, let's fix this by calling ttm_bo_del_from_lru() from
ttm_bo_move_to_lru_tail() in the event that we're dealing with a pinned
buffer. As well, add back the hunks in ttm_bo_del_from_lru() that were
removed which checked whether we want to call
bdev->driver->del_from_lru_notify() or not. We do this last part to avoid
calling the hook when the bo in question was already removed from the LRU.

Signed-off-by: Lyude Paul <lyude@...hat.com>
Fixes: 3d1a88e1051f ("drm/ttm: cleanup LRU handling further")
Cc: Christian König <christian.koenig@....com>
Cc: Dave Airlie <airlied@...hat.com>
---
 drivers/gpu/drm/ttm/ttm_bo.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 31e8b3da5563..0f373b78e7fa 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -113,11 +113,18 @@ static struct kobj_type ttm_bo_glob_kobj_type  = {
 static void ttm_bo_del_from_lru(struct ttm_buffer_object *bo)
 {
 	struct ttm_bo_device *bdev = bo->bdev;
+	bool notify = false;

-	list_del_init(&bo->swap);
-	list_del_init(&bo->lru);
+	if (!list_empty(&bo->swap)) {
+		notify = true;
+		list_del_init(&bo->swap);
+	}
+	if (!list_empty(&bo->lru)) {
+		notify = true;
+		list_del_init(&bo->lru);
+	}

-	if (bdev->driver->del_from_lru_notify)
+	if (notify && bdev->driver->del_from_lru_notify)
 		bdev->driver->del_from_lru_notify(bo);
 }

@@ -138,8 +145,13 @@ void ttm_bo_move_to_lru_tail(struct ttm_buffer_object *bo,

 	dma_resv_assert_held(bo->base.resv);

-	if (bo->pin_count)
+	/* Pinned bos will have been added to the LRU before they were pinned, so make sure we
+	 * always remove them here
+	 */
+	if (bo->pin_count) {
+		ttm_bo_del_from_lru(bo);
 		return;
+	}

 	man = ttm_manager_type(bdev, mem->mem_type);
 	list_move_tail(&bo->lru, &man->lru[bo->priority]);
-- 
2.29.2