Re: [PATCH 7.2.y] drm/ttm: fix swapped-out resources never leaving their bulk_move range

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Sep 22, 2026 at 06:33:34PM +0300, Vadim Nikitushkin wrote:
> commit 3db7d7d583419f7b1f2e141e36418802dbb25cf8 upstream.
> 
> ttm_tt_swapout() returns the number of pages swapped out on success and
> a negative error code on failure; for a populated ttm it never returns
> zero. Commit b2ed01e7ad3d ("drm/ttm: Fix ttm_bo_swapout() infinite LRU
> walk on swapout failure") moved the bulk_move bookkeeping in
> ttm_bo_swapout_cb() under "if (!ret)", so the
> ttm_resource_del_bulk_move_unevictable() / ttm_resource_move_to_lru_tail()
> pair is now skipped on every successful swapout. The equivalent change
> for the shrinker in commit 1d59f36e95f7 ("drm/ttm: Fix ttm_bo_shrink()
> infinite LRU walk on backup failure") tests "lret > 0", which is what
> was intended here as well.
> 
> Before b2ed01e7ad3d the resource was taken off the bulk_move before the
> swapout; since then a swapped-out resource stays inside its BO's
> bulk_move range (and on the manager LRU) although it is unevictable.
> When it is later freed or the BO leaves the bulk_move
> (ttm_resource_free(), ttm_bo_set_bulk_move() via amdgpu_vm_bo_del()),
> ttm_resource_del_bulk_move() skips it because of its
> !ttm_resource_unevictable() guard, so a range endpoint in pos->first /
> pos->last is left pointing at freed memory. The next
> ttm_lru_bulk_move_tail() or ttm_resource_add_bulk_move() on that cursor
> is a use-after-free, seen as the resv WARN in ttm_lru_bulk_move_add(),
> "list_del corruption" in ttm_resource_move_to_lru_tail() or a NULL
> dereference in ttm_resource_manager_next() -- minutes to hours after a
> hibernation, or at process exit / reboot following one. Samuel
> Ainsworth's analysis of drm/amd issue 5387 (see Link) identified the
> dangling cursor; the missing removal at swapout time is the reason it
> dangles.
> 
> Testing the condition for success restores the removal. On an AMD
> Phoenix APU (ASUS UM3406GA, gfx1103) running suspend-then-hibernate on
> a 7.0.y stable kernel carrying the backport (Ubuntu 7.0.0-31) the bug
> crashed 5 of 18 hibernation cycles; a function profile of one
> hibernation showed 336 ttm_tt_swapout() calls and zero
> ttm_resource_del_bulk_move_unevictable() calls. With this change the
> removal happens for every swapped-out resource and 12 further cycles
> were clean.
> 
> Fixes: b2ed01e7ad3d ("drm/ttm: Fix ttm_bo_swapout() infinite LRU walk on swapout failure")
> Cc: stable@vger.kernel.org # v7.1+
> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/5387
> Link: https://lore.kernel.org/dri-devel/CAHYiNPa6aVacJoLOje-qZ1GyYx-9p0tN4NuP8D_eSL+UJeevXw@mail.gmail.com/
> Signed-off-by: Vadim Nikitushkin <bub4z0r@gmail.com>
> Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Reviewed-by: Christian König <christian.koenig@amd.com>
> Signed-off-by: Christian König <christian.koenig@amd.com>
> Link: https://lore.kernel.org/r/20260909205028.13799-1-bub4z0r@gmail.com
> [ Squashed with commit fcfe64715b425262af1b36f498f9197f3537ceed

Do not squash, send a patch series instead please.

thanks,

greg k-h