[Mesa-dev] [PATCH v3] anv/allocator: Avoid race condition in anv_block_pool_map.

[Rafael Antognolli]

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).
v3: Move things around and only update center_bo_offset if not using
softpin too (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 | 20 ++++++++++++++------
 src/intel/vulkan/anv_private.h   | 13 +++++++++++++
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/src/intel/vulkan/anv_allocator.c b/src/intel/vulkan/anv_allocator.c
index 89f26789c85..006175c8c65 100644
--- a/src/intel/vulkan/anv_allocator.c
+++ b/src/intel/vulkan/anv_allocator.c
@@ -436,7 +436,9 @@ anv_block_pool_init(struct anv_block_pool *pool,
    pool->bo_flags = bo_flags;
    pool->nbos = 0;
    pool->size = 0;
+   pool->center_bo_offset = 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];
@@ -536,6 +538,7 @@ anv_block_pool_expand_range(struct anv_block_pool *pool,
       if (map == MAP_FAILED)
          return vk_errorf(pool->device->instance, pool->device,
                           VK_ERROR_MEMORY_MAP_FAILED, "gem mmap failed: %m");
+      assert(center_bo_offset == 0);
    } else {
       /* Just leak the old map until we destroy the pool.  We can't munmap it
        * without races or imposing locking on the block allocate fast path. On
@@ -549,6 +552,11 @@ anv_block_pool_expand_range(struct anv_block_pool *pool,
       if (map == MAP_FAILED)
          return vk_errorf(pool->device->instance, pool->device,
                           VK_ERROR_MEMORY_MAP_FAILED, "mmap failed: %m");
+
+      /* Now that we mapped the new memory, we can write the new
+       * center_bo_offset back into pool and update pool->map. */
+      pool->center_bo_offset = center_bo_offset;
+      pool->map = map + center_bo_offset;
       gem_handle = anv_gem_userptr(pool->device, map, size);
       if (gem_handle == 0) {
          munmap(map, size);
@@ -573,10 +581,6 @@ anv_block_pool_expand_range(struct anv_block_pool *pool,
    if (!pool->device->info.has_llc)
       anv_gem_set_caching(pool->device, gem_handle, I915_CACHING_CACHED);
 
-   /* Now that we successfull allocated everything, we can write the new
-    * center_bo_offset back into pool. */
-   pool->center_bo_offset = center_bo_offset;
-
    /* 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
     * placement : Wa32bitGeneralStateOffset and Wa32bitInstructionBaseOffset
@@ -670,8 +674,12 @@ 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