From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH] skb: Propagate pfmemalloc on skb from head page only Date: Thu, 14 Mar 2013 11:54:41 -0400 (EDT) Message-ID: <20130314.115441.1016076054622568752.davem@davemloft.net> References: <5141D0C4.70409@parallels.com> <1363270569.29475.11.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: xemul@parallels.com, mgorman@suse.de, netdev@vger.kernel.org, stable@kernel.org, kuznet@ms2.inr.ac.ru To: eric.dumazet@gmail.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:35053 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932394Ab3CNPy2 (ORCPT ); Thu, 14 Mar 2013 11:54:28 -0400 In-Reply-To: <1363270569.29475.11.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org List-ID: From: Eric Dumazet Date: Thu, 14 Mar 2013 15:16:09 +0100 > On Thu, 2013-03-14 at 17:29 +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: Eric Dumazet Applied and queued up for -stable, thanks.