anv/allocator: Use VG_NOACCESS_WRITE in anv_bo_pool_free

Previously, we were relying on the fact that VALGRIND_MEMPOOL_FREE came
later on in the function to prevent "link->bo = bo" from causing an invalid
write.  However, in the case where the size requested by the user is very
small (less than sizeof(struct anv_bo)), this isn't sufficient.  Instead,
we should call VALGRIND_MEMPOOL_FREE early and then use VG_NOACCESS_WRITE.
We do, however, have to call VALGRIND_MEMPOOL_FREE after reading bo_in
because it may be stored in the bo itself.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>

src/intel/vulkan/anv_allocator.c

@@ -865,15 +865,17 @@ anv_bo_pool_free(struct anv_bo_pool *pool, const struct anv_bo *bo_in)
 {
    /* Make a copy in case the anv_bo happens to be storred in the BO */
    struct anv_bo bo = *bo_in;
+
+   VG(VALGRIND_MEMPOOL_FREE(pool, bo.map));
+
    struct bo_pool_bo_link *link = bo.map;
-   link->bo = bo;
+   VG_NOACCESS_WRITE(&link->bo, bo);
 
    assert(util_is_power_of_two(bo.size));
    const unsigned size_log2 = ilog2_round_up(bo.size);
    const unsigned bucket = size_log2 - 12;
    assert(bucket < ARRAY_SIZE(pool->free_list));
 
-   VG(VALGRIND_MEMPOOL_FREE(pool, bo.map));
    anv_ptr_free_list_push(&pool->free_list[bucket], link);
 }