netdev - Re: [PATCH 09/13] netvm: Set PF_MEMALLOC as appropriate during SKB processing

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20110427092203.659fbc25@notabene.brown>
Date:	Wed, 27 Apr 2011 09:22:03 +1000
From:	NeilBrown <neilb@...e.de>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>,
	Linux-Netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 09/13] netvm: Set PF_MEMALLOC as appropriate during SKB
 processing

On Tue, 26 Apr 2011 15:10:48 +0100 Mel Gorman <mgorman@...e.de> wrote:

> On Tue, Apr 26, 2011 at 10:21:57PM +1000, NeilBrown wrote:
> > On Tue, 26 Apr 2011 08:36:50 +0100 Mel Gorman <mgorman@...e.de> wrote:
> > 
> > > diff --git a/net/core/dev.c b/net/core/dev.c
> > > index 3871bf6..2d79a20 100644
> > > --- a/net/core/dev.c
> > > +++ b/net/core/dev.c
> > > @@ -3095,6 +3095,27 @@ static void vlan_on_bond_hook(struct sk_buff *skb)
> > >  	}
> > >  }
> > >  
> > > +/*
> > > + * Limit which protocols can use the PFMEMALLOC reserves to those that are
> > > + * expected to be used for communication with swap.
> > > + */
> > > +static bool skb_pfmemalloc_protocol(struct sk_buff *skb)
> > > +{
> > > +	if (skb_pfmemalloc(skb))
> > > +		switch (skb->protocol) {
> > > +		case __constant_htons(ETH_P_ARP):
> > > +		case __constant_htons(ETH_P_IP):
> > > +		case __constant_htons(ETH_P_IPV6):
> > > +		case __constant_htons(ETH_P_8021Q):
> > > +			break;
> > > +
> > > +		default:
> > > +			return false;
> > > +		}
> > > +
> > > +	return true;
> > > +}
> > 
> > This sort of thing really bugs me :-)
> > Neither the comment nor the function name actually describe what the function
> > is doing.  The function is checking *2* things.
> >    is_pfmemalloc_skb_or_pfmemalloc_protocol()
> > might be a more correct name, but is too verbose.
> > 
> > I would prefer the skb_pfmemalloc test were removed from here and ....
> > 
> > > +	if (!skb_pfmemalloc_protocol(skb))
> > > +		goto drop;
> > > +
> > 
> > ...added here so this becomes:
> > 
> >       if (!skb_pfmemalloc(skb) && !skb_pfmemalloc_protocol(skb))
> >                 goto drop;
> > 
> > which actually makes sense.
> > 
> 
> Moving the check is neater but that check should be
> 
> 	if (skb_pfmemalloc(skb) && !skb_pfmemalloc_protocol(skb))
> 
> ? It's only if the skb was allocated from emergency reserves that we
> need to consider dropping it to make way for other packets to be
> received.
> 

Correct.  I got my Boolean algebra all confused. Sorry 'bout that.

NeilBrown
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html