Re: [RFC PATCH 02/16] drm/ttm/pool: Fix ttm_pool_alloc error path

[Christian König <christian.koenig@xxxxxxx>]

Am 15.02.23 um 19:02 schrieb Thomas Hellström:
> On Wed, 2023-02-15 at 18:31 +0100, Christian König wrote:
> > Am 15.02.23 um 17:13 schrieb Thomas Hellström:
> > > When hitting an error, the error path forgot to unmap dma mappings
> > > and
> > I don't see where this happens?
>  From what I can tell, ttm_pool_page_allocated() maps the page for dma,
> If we later hit an error, ttm_pool_free_page() will leak the mapping.

Ah, I see. Good point.

> > > could call set_pages_wb() on already uncached pages.
> > Yeah, but what's the problem?
> Umm, at least if you try to set WC on an already WC'd page, the
> set_pages_ code will spam dmesg with warnings.
> Not sure if set_pages_wb() on WB pages does the same, nor if it
> issues unnecessary global cache / tlb flushes or whether that will
> change in the future.
> The point of avoiding the set_pages_wb() when already WB is you don't
> have to check, and you don't have to care.

Please just open code the error handling then. That helper function 
looks horrible complicated to me.

Alternatively we could have a free function for a range of pages.

Regards,
Christian.


> That said, the __ttm_pool_free() is used also in upcoming patches.
>
> /Thomas
>
>
> > Regards,
> > Christian.
> >
> > > Fix this by introducing a common __ttm_pool_free() function that
> > > does the right thing.
> > >
> > > Fixes: d099fc8f540a ("drm/ttm: new TT backend allocation pool v3")
> > > Cc: Christian König <christian.koenig@xxxxxxx>
> > > Cc: Dave Airlie <airlied@xxxxxxxxxx>
> > > Cc: Madhav Chauhan <madhav.chauhan@xxxxxxx>
> > > Cc: Christian Koenig <christian.koenig@xxxxxxx>
> > > Cc: Huang Rui <ray.huang@xxxxxxx>
> > > Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > > Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> > > ---
> > >    drivers/gpu/drm/ttm/ttm_pool.c | 74 +++++++++++++++++++++--------
> > > -----
> > >    1 file changed, 45 insertions(+), 29 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/ttm/ttm_pool.c
> > > b/drivers/gpu/drm/ttm/ttm_pool.c
> > > index aa116a7bbae3..1cc7591a9542 100644
> > > --- a/drivers/gpu/drm/ttm/ttm_pool.c
> > > +++ b/drivers/gpu/drm/ttm/ttm_pool.c
> > > @@ -367,6 +367,39 @@ static int ttm_pool_page_allocated(struct
> > > ttm_pool *pool, unsigned int order,
> > >          return 0;
> > >    }
> > >    
> > > +static void __ttm_pool_free(struct ttm_pool *pool, struct ttm_tt
> > > *tt,
> > > +                           struct page **caching_divide,
> > > +                           enum ttm_caching initial_caching,
> > > +                           enum ttm_caching subseq_caching,
> > > +                           pgoff_t num_pages)
> > > +{
> > > +       enum ttm_caching caching = subseq_caching;
> > > +       struct page **pages = tt->pages;
> > > +       unsigned int order;
> > > +       pgoff_t i, nr;
> > > +
> > > +       if (pool && caching_divide)
> > > +               caching = initial_caching;
> > > +
> > > +       for (i = 0; i < num_pages; i += nr, pages += nr) {
> > > +               struct ttm_pool_type *pt = NULL;
> > > +
> > > +               if (unlikely(caching_divide == pages))
> > > +                       caching = subseq_caching;
> > > +
> > > +               order = ttm_pool_page_order(pool, *pages);
> > > +               nr = (1UL << order);
> > > +               if (tt->dma_address)
> > > +                       ttm_pool_unmap(pool, tt->dma_address[i],
> > > nr);
> > > +
> > > +               pt = ttm_pool_select_type(pool, caching, order);
> > > +               if (pt)
> > > +                       ttm_pool_type_give(pt, *pages);
> > > +               else
> > > +                       ttm_pool_free_page(pool, caching, order,
> > > *pages);
> > > +       }
> > > +}
> > > +
> > >    /**
> > >     * ttm_pool_alloc - Fill a ttm_tt object
> > >     *
> > > @@ -386,8 +419,9 @@ int ttm_pool_alloc(struct ttm_pool *pool,
> > > struct ttm_tt *tt,
> > >          dma_addr_t *dma_addr = tt->dma_address;
> > >          struct page **caching = tt->pages;
> > >          struct page **pages = tt->pages;
> > > +       enum ttm_caching page_caching;
> > >          gfp_t gfp_flags = GFP_USER;
> > > -       unsigned int i, order;
> > > +       unsigned int order;
> > >          struct page *p;
> > >          int r;
> > >    
> > > @@ -410,6 +444,7 @@ int ttm_pool_alloc(struct ttm_pool *pool,
> > > struct ttm_tt *tt,
> > >               order = min_t(unsigned int, order, __fls(num_pages)))
> > > {
> > >                  struct ttm_pool_type *pt;
> > >    
> > > +               page_caching = tt->caching;
> > >                  pt = ttm_pool_select_type(pool, tt->caching,
> > > order);
> > >                  p = pt ? ttm_pool_type_take(pt) : NULL;
> > >                  if (p) {
> > > @@ -418,6 +453,7 @@ int ttm_pool_alloc(struct ttm_pool *pool,
> > > struct ttm_tt *tt,
> > >                          if (r)
> > >                                  goto error_free_page;
> > >    
> > > +                       caching = pages;
> > >                          do {
> > >                                  r = ttm_pool_page_allocated(pool,
> > > order, p,
> > >                                                             
> > > &dma_addr,
> > > @@ -426,14 +462,15 @@ int ttm_pool_alloc(struct ttm_pool *pool,
> > > struct ttm_tt *tt,
> > >                                  if (r)
> > >                                          goto error_free_page;
> > >    
> > > +                               caching = pages;
> > >                                  if (num_pages < (1 << order))
> > >                                          break;
> > >    
> > >                                  p = ttm_pool_type_take(pt);
> > >                          } while (p);
> > > -                       caching = pages;
> > >                  }
> > >    
> > > +               page_caching = ttm_cached;
> > >                  while (num_pages >= (1 << order) &&
> > >                         (p = ttm_pool_alloc_page(pool, gfp_flags,
> > > order))) {
> > >    
> > > @@ -442,6 +479,7 @@ int ttm_pool_alloc(struct ttm_pool *pool,
> > > struct ttm_tt *tt,
> > >                                                             tt-
> > > > caching);
> > >                                  if (r)
> > >                                          goto error_free_page;
> > > +                               caching = pages;
> > >                          }
> > >                          r = ttm_pool_page_allocated(pool, order, p,
> > > &dma_addr,
> > >                                                      &num_pages,
> > > &pages);
> > > @@ -468,15 +506,12 @@ int ttm_pool_alloc(struct ttm_pool *pool,
> > > struct ttm_tt *tt,
> > >          return 0;
> > >    
> > >    error_free_page:
> > > -       ttm_pool_free_page(pool, tt->caching, order, p);
> > > +       ttm_pool_free_page(pool, page_caching, order, p);
> > >    
> > >    error_free_all:
> > >          num_pages = tt->num_pages - num_pages;
> > > -       for (i = 0; i < num_pages; ) {
> > > -               order = ttm_pool_page_order(pool, tt->pages[i]);
> > > -               ttm_pool_free_page(pool, tt->caching, order, tt-
> > > > pages[i]);
> > > -               i += 1 << order;
> > > -       }
> > > +       __ttm_pool_free(pool, tt, caching, tt->caching, ttm_cached,
> > > +                       num_pages);
> > >    
> > >          return r;
> > >    }
> > > @@ -492,27 +527,8 @@ EXPORT_SYMBOL(ttm_pool_alloc);
> > >     */
> > >    void ttm_pool_free(struct ttm_pool *pool, struct ttm_tt *tt)
> > >    {
> > > -       unsigned int i;
> > > -
> > > -       for (i = 0; i < tt->num_pages; ) {
> > > -               struct page *p = tt->pages[i];
> > > -               unsigned int order, num_pages;
> > > -               struct ttm_pool_type *pt;
> > > -
> > > -               order = ttm_pool_page_order(pool, p);
> > > -               num_pages = 1ULL << order;
> > > -               if (tt->dma_address)
> > > -                       ttm_pool_unmap(pool, tt->dma_address[i],
> > > num_pages);
> > > -
> > > -               pt = ttm_pool_select_type(pool, tt->caching,
> > > order);
> > > -               if (pt)
> > > -                       ttm_pool_type_give(pt, tt->pages[i]);
> > > -               else
> > > -                       ttm_pool_free_page(pool, tt->caching,
> > > order,
> > > -                                          tt->pages[i]);
> > > -
> > > -               i += num_pages;
> > > -       }
> > > +       __ttm_pool_free(pool, tt, NULL, tt->caching, tt->caching,
> > > +                       tt->num_pages);
> > >    
> > >          while (atomic_long_read(&allocated_pages) > page_pool_size)
> > >                  ttm_pool_shrink();