From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mel Gorman Subject: Re: [PATCH] skb: Propagate pfmemalloc on skb from head page only Date: Thu, 14 Mar 2013 14:28:24 +0000 Message-ID: <20130314142824.GE10369@suse.de> References: <5141D0C4.70409@parallels.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Cc: David Miller , Eric Dumazet , Linux Netdev List , stable@kernel.org, Alexey Kuznetsov To: Pavel Emelyanov Return-path: Received: from cantor2.suse.de ([195.135.220.15]:43546 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756672Ab3CNO2b (ORCPT ); Thu, 14 Mar 2013 10:28:31 -0400 Content-Disposition: inline In-Reply-To: <5141D0C4.70409@parallels.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, Mar 14, 2013 at 05:29:40PM +0400, Pavel Emelyanov wrote: > Hi. > > I'm trying to send big chunks of memory from application address space via > TCP socket using vmsplice + splice like this > > mem = mmap(128Mb); > vmsplice(pipe[1], mem); /* splice memory into pipe */ > splice(pipe[0], tcp_socket); /* send it into network */ > > When I'm lucky and a huge page splices into the pipe and then into the socket > _and_ client and server ends of the TCP connection are on the same host, > communicating via lo, the whole connection gets stuck! The sending queue > becomes full and app stops writing/splicing more into it, but the receiving > queue remains empty, and that's why. > > The __skb_fill_page_desc observes a tail page of a huge page and erroneously > propagates its page->pfmemalloc value onto socket (the pfmemalloc on tail pages > contain garbage). Then this skb->pfmemalloc leaks through lo and due to the > > tcp_v4_rcv > sk_filter > if (skb->pfmemalloc && !sock_flag(sk, SOCK_MEMALLOC)) /* true */ > return -ENOMEM > goto release_and_discard; > > no packets reach the socket. Even TCP re-transmits are dropped by this, as skb > cloning clones the pfmemalloc flag as well. > > That said, here's the proper page->pfmemalloc propagation onto socket: we > must check the huge-page's head page only, other pages' pfmemalloc and mapping > values do not contain what is expected in this place. However, I'm not sure > whether this fix is _complete_, since pfmemalloc propagation via lo also > oesn't look great. > > Both, bit propagation from page to skb and this check in sk_filter, were > introduced by c48a11c7 (netvm: propagate page->pfmemalloc to skb), in v3.5 so > Mel and stable@ are in Cc. > > Signed-off-by: Pavel Emelyanov > Acked-by: Mel Gorman -- Mel Gorman SUSE Labs