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ipx: fix locking regression in ipx_sendmsg and ipx_recvmsg 

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 <jbohac@suse.cz>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jiri Bohac 2014-11-19 23:05:49 +01:00 committed by David S. Miller
parent d3052bb5d3
commit 01462405f0
1 changed files with 5 additions and 1 deletions
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4
net/ipx/af_ipx.c
View File

@ -1764,6 +1764,7 @@ static int ipx_recvmsg(struct kiocb *iocb, struct socket *sock,
struct ipxhdr *ipx = NULL; struct ipxhdr *ipx = NULL;
struct sk_buff *skb; struct sk_buff *skb;
int copied, rc; int copied, rc;
bool locked = true;
lock_sock(sk); lock_sock(sk);
/* put the autobinding in */ /* put the autobinding in */
@ -1790,6 +1791,8 @@ static int ipx_recvmsg(struct kiocb *iocb, struct socket *sock,
if (sock_flag(sk, SOCK_ZAPPED)) if (sock_flag(sk, SOCK_ZAPPED))
goto out; goto out;
release_sock(sk);
locked = false;
skb = skb_recv_datagram(sk, flags & ~MSG_DONTWAIT, skb = skb_recv_datagram(sk, flags & ~MSG_DONTWAIT,
flags & MSG_DONTWAIT, &rc); flags & MSG_DONTWAIT, &rc);
if (!skb) { if (!skb) {
@ -1826,6 +1829,7 @@ static int ipx_recvmsg(struct kiocb *iocb, struct socket *sock,
out_free: out_free:
skb_free_datagram(sk, skb); skb_free_datagram(sk, skb);
out: out:
if (locked)
release_sock(sk); release_sock(sk);
return rc; return rc;
} }