[PATCH] drm/ttm: once more fix ttm_bo_bulk_move_lru_tail

[Huang Rui]

On Fri, Sep 14, 2018 at 05:22:16PM +0800, Michel Dänzer wrote:
> On 2018-09-14 10:22 a.m., Huang Rui wrote:
> > On Thu, Sep 13, 2018 at 07:32:24PM +0800, Christian König wrote:
> >> Am 13.09.2018 um 10:31 schrieb Huang Rui:
> >>> On Wed, Sep 12, 2018 at 09:23:55PM +0200, Christian König wrote:
> >>>> While cutting the lists we sometimes accidentally added a list_head from
> >>>> the stack to the LRUs, effectively corrupting the list.
> >>>>
> >>>> Remove the list cutting and use explicit list manipulation instead.
> >>> This patch actually fixes the corruption bug. Was it a defect of
> >>> list_cut_position or list_splice handlers?
> >>
> >> We somehow did something illegal with list_cut_position. I haven't 
> >> narrowed it down till the end, but we ended up with list_heads from the 
> >> stack to the lru.
> > 
> > I am confused, in theory, even we do any manipulation with list helper, it
> > should not trigger the list corruption. The usage of those helpers should
> > ensure the list operation safely...
> 
> There's nothing the helpers can do about being passed in pointers to
> stack memory. It's a bug in the code using the helpers.
> 

Actually, I was checking carefully with list cut and splice in our case,
and it didn't find any illegal use. However, I also agree with the explicit
list manipulation is more clear and simple for now.

Thanks,
Ray