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ipx: fix locking regression in ipx_sendmsg and ipx_recvmsg

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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 <[email protected]>
Reviewed-by: Arnd Bergmann <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Jiri Bohac 2014-11-19 23:05:49 +01:00 • committed by David S. Miller
commit 01462405f0
1 changed files with 5 additions and 1 deletions
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6
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 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) {
@ -1826,7 +1829,8 @@ 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;
}