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

From: "Christian König" <christian.koenig@amd.com>
To: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>,
	dri-devel@lists.freedesktop.org
Cc: Dave Airlie <airlied@redhat.com>,
	Madhav Chauhan <madhav.chauhan@amd.com>,
	Huang Rui <ray.huang@amd.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	Miaohe Lin <linmiaohe@huawei.com>,
	David Hildenbrand <david@redhat.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Peter Xu <peterx@redhat.com>, NeilBrown <neilb@suse.de>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	Dave Hansen <dave.hansen@intel.com>,
	Matthew Auld <matthew.auld@intel.com>,
	linux-graphics-maintainer@vmware.com, linux-mm@kvack.org,
	intel-gfx@lists.freedesktop.org
Subject: Re: [RFC PATCH 02/16] drm/ttm/pool: Fix ttm_pool_alloc error path
Date: Wed, 15 Feb 2023 19:26:23 +0100	[thread overview]
Message-ID: <63d9b7a9-1d03-c434-df77-055969c42517@amd.com> (raw)
In-Reply-To: <85166ca49f556c9faef7a0d76cb1e826c0014ce6.camel@linux.intel.com>

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@amd.com>
>>> Cc: Dave Airlie <airlied@redhat.com>
>>> Cc: Madhav Chauhan <madhav.chauhan@amd.com>
>>> Cc: Christian Koenig <christian.koenig@amd.com>
>>> Cc: Huang Rui <ray.huang@amd.com>
>>> Cc: dri-devel@lists.freedesktop.org
>>> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>>> ---
>>>    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();