linux-kernel - Re: [PATCH 3/4]percpu_counter: fix code for 32bit systems

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Message-ID: <1302661927.2811.18.camel@edumazet-laptop>
Date:	Wed, 13 Apr 2011 04:32:07 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"cl@...ux.com" <cl@...ux.com>, "tj@...nel.org" <tj@...nel.org>
Subject: Re: [PATCH 3/4]percpu_counter: fix code for 32bit systems

Le mercredi 13 avril 2011 à 09:01 +0800, Shaohua Li a écrit :
> On Tue, 2011-04-12 at 17:03 +0800, Eric Dumazet wrote:
> > 
> > Hmm... did you test this with LOCKDEP on ?
> > 
> > You add a possible deadlock here.
> > 
> > Hint : Some percpu_counter are used from irq context.
> there are some places we didn't disable interrupt, for example
> percpu_counter_add. So the API isn't irq safe to me.
> 

So what ? Callers must disable IRQ before calling percpu_counter_add(),
and they actually do in network stack. Please check again,
tcp_sockets_allocated for example.

> > This interface assumes caller take the appropriate locking.
> no comments say this, and some places we don't hold locking.
> for example, meminfo_proc_show.
> 

This doesnt answer my question about LOCKDEP ;)

Just fix the few callers that might need a fix, since this is the only
way to deal with potential problems without adding performance penalty
(for stable trees)



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