On Sat Mar 1 22:56:25 EST 2014, cinap_len...@felloff.net wrote:
> checked nix/port/page.c. your duppage() is wrong.
>
> /* don't dup pages with no image */
> if(p->ref == 0 || p->image == nil || p->image->notext)
> return 0;
>
> /*
> * normal lock ordering is to call
> * lock(&pga) before lock(p).
> * To avoid deadlock, we have to drop
> * our locks and try again.
> */
> if(!canlock(&pga)){
> unlock(p);
> if(up)
> sched();
> lock(p);
> goto retry;
> }
>
> you need to check p->ref != 1 instead of p->ref == 0. the page
> passed to duppage() is still cached. after you unlock(p), someone
> can come in and take a reference to the page from the image
> cache (lookpage()), making p->ref > 1 once you get the lock back.
>
> put an assert or print in there after the if(!canlock(&pga){} block
> to check p->ref.
why do i need an assert or print after the unlock? it should go back
through the loop and notice p->ref != 1.
- erik
