[PATCH] Harden tcache double-free check

[Florian Weimer]

* Siddhesh Poyarekar:

> +/* Process-wide key to try and catch a double-free in the same thread.  */
> +static uintptr_t tcache_key;
> +
> +/* The value of tcache_key does not really have to be a cryptographically
> +   secure random number.  It only needs to be arbitrary enough so that it does
> +   not collide with values present in applications, which would be quite rare,
> +   about 1 in 2^wordsize.  */

The comment should say that a collision could result in performance
problems.

Apart from that, the patch looks okay to me.

Thanks,
Florian