[PATCH 6.1.y] drm/ttm: fix bulk_move corruption when adding a entry

[Yunxiang Li <Yunxiang.Li@amd.com>]

When the resource is the first in the bulk_move range, adding it again
(thus moving it to the tail) will corrupt the list since the first
pointer is not moved. This eventually lead to null pointer deref in
ttm_lru_bulk_move_del()

Fixes: fee2ede15542 ("drm/ttm: rework bulk move handling v5")
Signed-off-by: Yunxiang Li <Yunxiang.Li@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
CC: stable@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20230622141902.28718-3-Yunxiang.Li@amd.com
Signed-off-by: Christian König <christian.koenig@amd.com>
(cherry picked from commit 4481913607e58196c48a4fef5e6f45350684ec3c)
---
 drivers/gpu/drm/ttm/ttm_resource.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/ttm/ttm_resource.c b/drivers/gpu/drm/ttm/ttm_resource.c
index a729c32a1e48..3287032a2f8e 100644
--- a/drivers/gpu/drm/ttm/ttm_resource.c
+++ b/drivers/gpu/drm/ttm/ttm_resource.c
@@ -85,6 +85,8 @@ static void ttm_lru_bulk_move_pos_tail(struct ttm_lru_bulk_move_pos *pos,
 				       struct ttm_resource *res)
 {
 	if (pos->last != res) {
+		if (pos->first == res)
+			pos->first = list_next_entry(res, lru);
 		list_move(&res->lru, &pos->last->lru);
 		pos->last = res;
 	}
@@ -110,7 +112,8 @@ static void ttm_lru_bulk_move_del(struct ttm_lru_bulk_move *bulk,
 {
 	struct ttm_lru_bulk_move_pos *pos = ttm_lru_bulk_move_pos(bulk, res);
 
-	if (unlikely(pos->first == res && pos->last == res)) {
+	if (unlikely(WARN_ON(!pos->first || !pos->last) ||
+		     (pos->first == res && pos->last == res))) {
 		pos->first = NULL;
 		pos->last = NULL;
 	} else if (pos->first == res) {
-- 
2.41.0