From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jiri Bohac Subject: [PATCH v4] ipx: fix locking regression in ipx_sendmsg and ipx_recvmsg Date: Wed, 19 Nov 2014 23:05:49 +0100 Message-ID: <20141119220549.GA26133@midget.suse.cz> References: <1609909.1jJeqOzgZ8@wuerfel> <20141119103413.GA19092@midget.suse.cz> <20141119103814.GB19092@midget.suse.cz> <20141119.154400.1045032776950540216.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: jbohac@suse.cz, arnd@arndb.de, acme@ghostprotocols.net, netdev@vger.kernel.org To: David Miller Return-path: Received: from cantor2.suse.de ([195.135.220.15]:42199 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756504AbaKSWFw (ORCPT ); Wed, 19 Nov 2014 17:05:52 -0500 Content-Disposition: inline In-Reply-To: <20141119.154400.1045032776950540216.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: This fixes an old regression introduced by commit b0d0d915 (ipx: remove the BKL). When a recvmsg syscall blocks waiting for new data, no data can be sent on the same socket with sendmsg because ipx_recvmsg() sleeps with the socket locked. This breaks mars-nwe (NetWare emulator): - the ncpserv process reads the request using recvmsg - ncpserv forks and spawns nwconn - ncpserv calls a (blocking) recvmsg and waits for new requests - nwconn deadlocks in sendmsg on the same socket Commit b0d0d915 has simply replaced BKL locking with lock_sock/release_sock. Unlike now, BKL got unlocked while sleeping, so a blocking recvmsg did not block a concurrent sendmsg. Only keep the socket locked while actually working with the socket data and release it prior to calling skb_recv_datagram(). Signed-off-by: Jiri Bohac diff --git a/net/ipx/af_ipx.c b/net/ipx/af_ipx.c index a0c7536..d0725d9 100644 --- a/net/ipx/af_ipx.c +++ b/net/ipx/af_ipx.c @@ -1764,6 +1764,7 @@ static int ipx_recvmsg(struct kiocb *iocb, struct socket *sock, struct ipxhdr *ipx = NULL; struct sk_buff *skb; int copied, rc; + bool locked = true; lock_sock(sk); /* put the autobinding in */ @@ -1790,6 +1791,8 @@ static int ipx_recvmsg(struct kiocb *iocb, struct socket *sock, if (sock_flag(sk, SOCK_ZAPPED)) goto out; + release_sock(sk); + locked = false; skb = skb_recv_datagram(sk, flags & ~MSG_DONTWAIT, flags & MSG_DONTWAIT, &rc); if (!skb) { @@ -1825,7 +1828,8 @@ static int ipx_recvmsg(struct kiocb *iocb, struct socket *sock, out_free: skb_free_datagram(sk, skb); out: - release_sock(sk); + if (locked) + release_sock(sk); return rc; } -- Jiri Bohac SUSE Labs, SUSE CZ