memory leak in free()

[Jason Evans]

Ville-Pertti Keinonen wrote:
> 
> On Jun 14, 2006, at 8:35 PM, Jason Evans wrote:
> 
>> Incidentally, this isn't an issue on 64-bit systems, since only mmap 
>> () is used to request memory from the kernel.
> 
> 
> The test does seem to leak memory on 64-bit systems, though; not the  
> actual allocated bits, but support structures, namely nodes that  
> chunk_dealloc tries to insert into old_chunks but fails because a  node 
> holding that address is already there.
> 
> It should be possible to fix this either by removing any nodes within  
> range from old_chunks when allocating "new" memory, or by checking  the 
> return value of RB_INSERT in chunk_dealloc, and deallocating the  new 
> node if it returns non-NULL.
> 
> A patch implementing the latter that seems to work:
> 
> --- malloc.c    10 May 2006 00:07:45 -0000      1.126
> +++ malloc.c    19 Jun 2006 13:58:57 -0000
> @@ -1370,7 +1370,8 @@
>                 node->chunk = (void *)((uintptr_t)chunk + (uintptr_t) 
> offset);
>                 node->size = chunk_size;
> -               RB_INSERT(chunk_tree_s, &old_chunks, node);
> +               if (RB_INSERT(chunk_tree_s, &old_chunks, node) != NULL)
> +                       base_chunk_node_dealloc(node);
>         }
> #ifdef USE_BRK

Ah, you are right that there is a leak.  I'm going to use a slightly 
different approach to fixing the problem, but thank you very much for 
pointing it out.

Jason