netdev - Re: [PATCH net-next-2.6] pkt_sched: gen_estimator: kill est

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Date:	Mon, 07 Jun 2010 17:55:51 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Stephen Hemminger <shemminger@...tta.com>,
	Jarek Poplawski <jarkao2@...il.com>
Subject: Re: [PATCH net-next-2.6] pkt_sched: gen_estimator: kill est_lock 
 rwlock

Le lundi 07 juin 2010 à 17:30 +0200, Eric Dumazet a écrit :
> Le lundi 07 juin 2010 à 22:53 +0800, Changli Gao a écrit :
> 
> > Hmm. I don't think it is correct.
> > 
> > Look at this code:
> > 
> > void xt_rateest_put(struct xt_rateest *est)
> > {
> >         mutex_lock(&xt_rateest_mutex);
> >         if (--est->refcnt == 0) {
> >                 hlist_del(&est->list);
> >                 gen_kill_estimator(&est->bstats, &est->rstats);
> >                 kfree(est);
> >         }
> >         mutex_unlock(&xt_rateest_mutex);
> > }
> > 
> > est will be released after gen_kill_estimator() returns. After est is
> > freed, there may still be some other CPUs running in the branch:
> >      if (bstats) {
> >          ....
> >      }
> > 
> 
> Oh well, I think I knew this from a previous attempt, but then I
> forgot :)
> 
> I'll provide an updated patch, so that no other attempt is tried next
> yer, thanks !
> 
> 

For your information, bug is already there before my patch.

So this est_lock is a wrong protection, in the sense its so convoluted
that nobody but you and me even noticed it was buggy in the first place.

(see commit 5d944c640b4 for a first patch)



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