Hi Greg,
On 9/23/26 09:41, Greg KH wrote:
> 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: [email protected] # v7.1+
>> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/5387
>> Link:
>> https://lore.kernel.org/dri-devel/cahyinpa6avacjoloje-qz1gyyx-9p0tn4nup8d_esl+ujee...@mail.gmail.com/
>> Signed-off-by: Vadim Nikitushkin <[email protected]>
>> Reviewed-by: Thomas Hellström <[email protected]>
>> Reviewed-by: Christian König <[email protected]>
>> Signed-off-by: Christian König <[email protected]>
>> Link: https://lore.kernel.org/r/[email protected]
>> [ Squashed with commit fcfe64715b425262af1b36f498f9197f3537ceed
>
> Do not squash, send a patch series instead please.
in this particular case that squashing is the correct approach.
AMDs mail servers mangled the initial patch so badly that I had trouble
applying it and ended up pushing a broken patch upstream. The squash is
basically fixing that up.
Back-porting each patch individually doesn't make much sense, you would just
end up with a broken tree in between.
Sorry for that,
Christian.
>
> thanks,
>
> greg k-h
