From: erik quanstrom <quanstro@quanstro.net>
To: 9fans@9fans.net
Subject: Re: [9fans] imagereclaim()
Date: Sat, 1 Mar 2014 23:05:19 -0500 [thread overview]
Message-ID: <0b927c978635da089774a72c0af3de19@mikro.quanstro.net> (raw)
In-Reply-To: <122a1b862278abf61a07a806168993ac@felloff.net>
On Sat Mar 1 22:56:25 EST 2014, cinap_lenrek@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
next prev parent reply other threads:[~2014-03-02 4:05 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-01 21:46 cinap_lenrek
2014-03-01 21:55 ` erik quanstrom
2014-03-01 22:22 ` cinap_lenrek
2014-03-01 22:52 ` erik quanstrom
2014-03-01 23:05 ` cinap_lenrek
2014-03-01 23:11 ` erik quanstrom
2014-03-01 23:14 ` Charles Forsyth
2014-03-02 1:21 ` cinap_lenrek
2014-03-02 3:14 ` erik quanstrom
2014-03-02 3:55 ` cinap_lenrek
2014-03-02 4:05 ` erik quanstrom [this message]
2014-03-02 4:30 ` cinap_lenrek
2014-03-02 9:48 ` Charles Forsyth
2014-03-02 18:46 ` cinap_lenrek
2014-03-02 18:53 ` Charles Forsyth
2014-03-02 22:59 ` Anthony Martin
2014-03-03 1:00 ` erik quanstrom
2014-03-01 23:09 ` Charles Forsyth
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