From 3e5b12de56d8fae345d3b331a14bc06f7609a992 Mon Sep 17 00:00:00 2001 From: Jiri Bohac Date: Wed, 19 Nov 2014 23:05:49 +0100 Subject: [PATCH] ipx: fix locking regression in ipx_sendmsg and ipx_recvmsg [ Upstream commit 01462405f0c093b2f8dfddafcadcda6c9e4c5cdf ] 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 Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/ipx/af_ipx.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/net/ipx/af_ipx.c b/net/ipx/af_ipx.c index e0897377b3b4..2665bf4b8d05 100644 --- a/net/ipx/af_ipx.c +++ b/net/ipx/af_ipx.c @@ -1778,6 +1778,7 @@ 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 */ @@ -1804,6 +1805,8 @@ 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) @@ -1837,7 +1840,8 @@ 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; }