[Mesa-dev] [PATCH v2] anv/allocator: Avoid race condition in anv_block_pool_map.

[Jason Ekstrand]

On Wed, Jan 23, 2019 at 5:26 PM Rafael Antognolli <
rafael.antognolli at intel.com> wrote:

> Accessing bo->map and then pool->center_bo_offset without a lock is
> racy. One way of avoiding such race condition is to store the bo->map +
> center_bo_offset into pool->map at the time the block pool is growing,
> which happens within a lock.
>
> v2: Only set pool->map if not using softpin (Jason).
>
> Cc: Jason Ekstrand <jason at jlekstrand.net>
> Reported-by: Ian Romanick <idr at freedesktop.org>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109442
> Fixes: fc3f58832015cbb177179e7f3420d3611479b4a9
> ---
>  src/intel/vulkan/anv_allocator.c | 11 +++++++++--
>  src/intel/vulkan/anv_private.h   | 13 +++++++++++++
>  2 files changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/src/intel/vulkan/anv_allocator.c
> b/src/intel/vulkan/anv_allocator.c
> index 89f26789c85..67f9c2a948d 100644
> --- a/src/intel/vulkan/anv_allocator.c
> +++ b/src/intel/vulkan/anv_allocator.c
> @@ -437,6 +437,7 @@ anv_block_pool_init(struct anv_block_pool *pool,
>     pool->nbos = 0;
>     pool->size = 0;
>     pool->start_address = gen_canonical_address(start_address);
> +   pool->map = NULL;
>
>     /* This pointer will always point to the first BO in the list */
>     pool->bo = &pool->bos[0];
> @@ -576,6 +577,8 @@ anv_block_pool_expand_range(struct anv_block_pool
> *pool,
>     /* Now that we successfull allocated everything, we can write the new
>      * center_bo_offset back into pool. */
>     pool->center_bo_offset = center_bo_offset;
> +   if (!use_softpin)
> +      pool->map = map + center_bo_offset;
>

We could also put this a bit higher up right after where we actually call
mmap.  That would reduce the number of "if (use_softpin)" blocks and
probably make things more readable.

Come to think of it, we could also set pool->center_bo_offset there and
just assert(center_bo_offset == 0) in the softpin case.  I like that.
Maybe that's a second patch?

In any case, this fixes today's bug

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>

--Jason


>
>     /* For block pool BOs we have to be a bit careful about where we place
> them
>      * in the GTT.  There are two documented workarounds for state base
> address
> @@ -670,8 +673,12 @@ anv_block_pool_get_bo(struct anv_block_pool *pool,
> int32_t *offset)
>  void*
>  anv_block_pool_map(struct anv_block_pool *pool, int32_t offset)
>  {
> -   struct anv_bo *bo = anv_block_pool_get_bo(pool, &offset);
> -   return bo->map + pool->center_bo_offset + offset;
> +   if (pool->bo_flags & EXEC_OBJECT_PINNED) {
> +      struct anv_bo *bo = anv_block_pool_get_bo(pool, &offset);
> +      return bo->map + offset;
> +   } else {
> +      return pool->map + offset;
> +   }
>  }
>
>  /** Grows and re-centers the block pool.
> diff --git a/src/intel/vulkan/anv_private.h
> b/src/intel/vulkan/anv_private.h
> index 3889065c93c..110b2ccf023 100644
> --- a/src/intel/vulkan/anv_private.h
> +++ b/src/intel/vulkan/anv_private.h
> @@ -663,6 +663,19 @@ struct anv_block_pool {
>      */
>     uint32_t center_bo_offset;
>
> +   /* Current memory map of the block pool.  This pointer may or may not
> +    * point to the actual beginning of the block pool memory.  If
> +    * anv_block_pool_alloc_back has ever been called, then this pointer
> +    * will point to the "center" position of the buffer and all offsets
> +    * (negative or positive) given out by the block pool alloc functions
> +    * will be valid relative to this pointer.
> +    *
> +    * In particular, map == bo.map + center_offset
> +    *
> +    * DO NOT access this pointer directly. Use anv_block_pool_map()
> instead,
> +    * since it will handle the softpin case as well, where this points to
> NULL.
> +    */
> +   void *map;
>     int fd;
>
>     /**
> --
> 2.17.2
>
>
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