On Fri, Sep 07, 2018 at 07:18:59PM +0800, Christian K�nig wrote: > Am 07.09.2018 um 13:02 schrieb Huang, Ray: > > Yes, that was one problem. Another was that the cutting code was buggy > and determined one of the positions to cut at the wrong time. > > I went through again about the list cutting behavior and wrote down with the attached picture. > After do the second list_cut_position, the list2 should be point the end of "before" list. And list2 won't be used anymore after list cutting. May I know am I something missed? > > > Let's take a look at the original code: > > list1 = is_swap ? &pos->last->swap : &pos->last->lru; > list2 = is_swap ? pos->first->swap.prev : pos->first->lru.prev; > > list_cut_position(&entries, lru, list1); > list_cut_position(&before, &entries, list2); > > > As far as I can see the problem is that the first list_cur_position could > modify the value of pos->first->lru.prev and so make the second > list_cut_position work on the wrong position. > I think I understood. In this case (the first element of LRU == pos->first->lru), please see the picture. If we store first->lru.prev as list2(LRU head), after do list cutting, the first->lru.prev will overwrite as new head (entries), however, the orignal list2 will still point previous head (that is the wrong position now). We actually expected to use the latest first->lru.prev as the second cutting position. So we should adjust code sequence like below: list1 = is_swap ? &pos->last->swap : &pos->last->lru; list_cut_position(&entries, lru, list1); list2 = is_swap ? pos->first->swap.prev : pos->first->lru.prev; list_cut_position(&before, &entries, list2); Am I understanding right? Thanks, Ray > Regards, > Christian. > > > > Thanks, > Ray > > From: amd-gfx on behalf of Christian König > Sent: Thursday, September 6, 2018 6:06 PM > To: Huang, Ray > Cc: Michel Dänzer; amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org > Subject: Re: [PATCH 1/3] drm/ttm: fix ttm_bo_bulk_move_helper > > > Am 06.09.2018 um 12:02 schrieb Huang Rui: > > On Fri, Aug 31, 2018 at 05:17:33PM +0200, Christian König wrote: > > Am 31.08.2018 um 17:15 schrieb Michel Dänzer: > > On 2018-08-31 3:10 p.m., Christian König wrote: > > Staring at the function for six hours, just to essentially move one line > of code. > > That sucks, but the commit log should describe what the problem was and > how this patch solves it. > > > > Signed-off-by: Christian König > --- > drivers/gpu/drm/ttm/ttm_bo.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c > index 35d53d81f486..138c98902033 100644 > --- a/drivers/gpu/drm/ttm/ttm_bo.c > +++ b/drivers/gpu/drm/ttm/ttm_bo.c > @@ -250,15 +250,18 @@ EXPORT_SYMBOL(ttm_bo_move_to_lru_tail); > static void ttm_bo_bulk_move_helper(struct ttm_lru_bulk_move_pos *pos, > struct list_head *lru, bool is_swap) > { > + struct list_head *list; > LIST_HEAD(entries); > LIST_HEAD(before); > - struct list_head *list1, *list2; > - list1 = is_swap ? &pos->last->swap : &pos->last->lru; > - list2 = is_swap ? pos->first->swap.prev : pos->first->lru.prev; > + reservation_object_assert_held(pos->last->resv); > + list = is_swap ? &pos->last->swap : &pos->last->lru; > + list_cut_position(&entries, lru, list); > + > + reservation_object_assert_held(pos->first->resv); > + list = is_swap ? pos->first->swap.prev : pos->first->lru.prev; > + list_cut_position(&before, &entries, list); > > So the problem was that the first list_cut_position call could result in > list2 pointing to la-la-land? Good catch! > > Yes, exactly. Thought that would be obvious, but going to add that > to the commit log. > > Can I get a tested-by? You where much better at reproducing that than I'm. > > > Michel, Christian, thanks so much to take care of this when I was on > vacation. And sorry to let you take a long time for finding the cause. > > Is that because I didn't hold the resveration before cut the list from > position "first" and "last"? > > Yes, that was one problem. Another was that the cutting code was buggy > and determined one of the positions to cut at the wrong time. > > > May I know in which cases, we must hold the > bo's reservation firstly? > > BOs are reserved to prevent moving them. E.g. when the BO isn't reserved > it can move around and so the LRU where you want to add/remove it could > change. > > Christian. > > > Thanks, > Ray > > > > _______________________________________________ > amd-gfx mailing list > amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org > https://lists.freedesktop.org/mailman/listinfo/amd-gfx > > > amd-gfx Info Page - freedesktop.org > lists.freedesktop.org > To see the collection of prior postings to the list, visit the amd-gfx Archives.. Using amd-gfx: To post a message to all the list members, send email to amd-gfx-PD4FTy7X32lNgt0PjOBp9xlNPtJONSTn@public.gmane.org You can subscribe to the list, or change your existing subscription, in the sections below. > > > > > > _______________________________________________ > amd-gfx mailing list > amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org > https://lists.freedesktop.org/mailman/listinfo/amd-gfx > >