Commit b2ed01e7 authored by Thomas Hellström's avatar Thomas Hellström
Browse files

drm/ttm: Fix ttm_bo_swapout() infinite LRU walk on swapout failure 



When ttm_tt_swapout() fails, the current code calls
ttm_resource_add_bulk_move() followed by ttm_resource_move_to_lru_tail()
to restore the resource's bulk_move membership.

However, ttm_resource_move_to_lru_tail() places the resource at the tail
of the LRU list which, relative to the walk cursor's hitch node (placed
immediately after the resource when it was yielded), puts the resource
*in front of the* the hitch. The next list_for_each_entry_continue() from
the hitch finds the same resource again, causing an infinite loop.

Fix by deferring del_bulk_move to the success path only.

On the success path, TTM_TT_FLAG_SWAPPED has just been set by
ttm_tt_swapout() but the resource is still tracked in the bulk_move range,
so ttm_resource_del_bulk_move()'s !ttm_resource_unevictable() guard would
incorrectly skip the removal. Introduce
ttm_resource_del_bulk_move_unevictable() which bypasses that guard.

Reported-by: default avatarJatin Kataria <jkataria@netflix.com>
Fixes: fc5d9667 ("drm/ttm: Move swapped objects off the manager's LRU list")
Cc: Christian König <christian.koenig@amd.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: <dri-devel@lists.freedesktop.org>
Cc: <stable@vger.kernel.org> # v6.13+
Assisted-by: GitHub_Copilot:claude-sonnet-4.6
Signed-off-by: default avatarThomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: default avatarChristian König <christian.koenig@amd.com>
Tested-by: default avatarBoqun Feng <boqun@kernel.org>
Link: https://patch.msgid.link/20260428094442.16985-1-thomas.hellstrom@linux.intel.com
parent 459d7552

drivers/gpu/drm/ttm/ttm_bo.c

+6 −10
Original line number Diff line number Diff line
@@ -1177,18 +1177,14 @@ ttm_bo_swapout_cb(struct ttm_lru_walk *walk, struct ttm_buffer_object *bo) 
		bdev->funcs->swap_notify(bo);



	if (ttm_tt_is_populated(tt)) {

		spin_lock(&bdev->lru_lock);

		ttm_resource_del_bulk_move(bo->resource, bo);

		spin_unlock(&bdev->lru_lock);



		ret = ttm_tt_swapout(bdev, tt, swapout_walk->gfp_flags);



		if (!ret) {

			spin_lock(&bdev->lru_lock);

		if (ret)

			ttm_resource_add_bulk_move(bo->resource, bo);

			ttm_resource_del_bulk_move_unevictable(bo->resource, bo);

			ttm_resource_move_to_lru_tail(bo->resource);

			spin_unlock(&bdev->lru_lock);

		}

	}



out:

	/* Consider -ENOMEM and -ENOSPC non-fatal. */

drivers/gpu/drm/ttm/ttm_resource.c

+13 −0
Original line number Diff line number Diff line
@@ -292,6 +292,19 @@ void ttm_resource_del_bulk_move(struct ttm_resource *res, 
		ttm_lru_bulk_move_del(bo->bulk_move, res);

}



/*

 * Remove a resource from its bulk_move, bypassing the unevictable check.

 * Use only when the resource is known to still be tracked in the range despite

 * the BO having just become unevictable; asserts that this is the case.

 */

void ttm_resource_del_bulk_move_unevictable(struct ttm_resource *res,

					    struct ttm_buffer_object *bo)

{

	WARN_ON_ONCE(!ttm_resource_unevictable(res, bo));

	if (bo->bulk_move)

		ttm_lru_bulk_move_del(bo->bulk_move, res);

}



/* Move a resource to the LRU or bulk tail */

void ttm_resource_move_to_lru_tail(struct ttm_resource *res)

{

include/drm/ttm/ttm_resource.h

+2 −0
Original line number Diff line number Diff line
@@ -448,6 +448,8 @@ void ttm_resource_add_bulk_move(struct ttm_resource *res, 
				struct ttm_buffer_object *bo);

void ttm_resource_del_bulk_move(struct ttm_resource *res,

				struct ttm_buffer_object *bo);

void ttm_resource_del_bulk_move_unevictable(struct ttm_resource *res,

					    struct ttm_buffer_object *bo);

void ttm_resource_move_to_lru_tail(struct ttm_resource *res);



void ttm_resource_init(struct ttm_buffer_object *bo,