From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH v4] ipx: fix locking regression in ipx_sendmsg and ipx_recvmsg Date: Wed, 19 Nov 2014 23:12:21 +0100 Message-ID: <3682315.1qi3iAkNAF@wuerfel> References: <1609909.1jJeqOzgZ8@wuerfel> <20141119.154400.1045032776950540216.davem@davemloft.net> <20141119220549.GA26133@midget.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: David Miller , acme@ghostprotocols.net, netdev@vger.kernel.org To: Jiri Bohac Return-path: Received: from mout.kundenserver.de ([212.227.17.24]:51306 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933287AbaKSWMj (ORCPT ); Wed, 19 Nov 2014 17:12:39 -0500 In-Reply-To: <20141119220549.GA26133@midget.suse.cz> Sender: netdev-owner@vger.kernel.org List-ID: On Wednesday 19 November 2014 23:05:49 Jiri Bohac wrote: > 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 > Reviewed-by: Arnd Bergmann