It happens when some memory was freed to the pool and then modified after

it was freed.
//art
"banana split"  writes:
> hello,

quoted text
>

> I've a question (maybe a stupid one). I have a problem with a box so I'm start

> searching the reason of this problem. By reading the code I'm wondering what

> are the circumstances under which the code panics in pool_do_get (different

> sentinel values...) specifically in

>

> #ifdef DIAGNOSTIC

>      if (__predict_false(pi->pi_magic != PI_MAGIC)) {

>            panic("pool_do_get(%s): free list modified: magic=%x; page %p;"

>                  " item addr %p",

>                  pp->pr_wchan, pi->pi_magic, ph->ph_page, pi);

>      }

> #endif

>

> really thanks for any explanation/example and/or something to read on the

> matter