[patch] tcache double free check

[Florian Weimer]

* DJ Delorie:

> +  /* This test succeeds on double free.  However, we don't 100% trust
> +     it, so verify it's not an unlikely coincidence before
> +     aborting.  */
> +  if (__glibc_unlikely (e->key == tcache))
> +    {
> +      tcache_entry *tmp;
> +      for (tmp = tcache->entries[tc_idx];
> +	   tmp;
> +	   tmp = tmp->next)
> +	{
> +	if (tmp == e)
> +	  malloc_printerr ("free(): double free detected in tcache");
> +	}
> +      /* If we get here, it was a coincidence.  We've wasted a few
> +	 cycles, but don't abort.  */
> +    }

One more thing:

I think you should put an Systemtap probe here, perhaps counting the
length of the chain and logging the index, so that we can debug
performance issues here.

Thanks,
Florian