This patch is suitable for just about any 2.6 kernel.  It should go in
2.6.19 and 2.6.18.2 and possible even the .17 and .16 stable series.

This is a long standing bug that seems to have only recently become
apparent, presumably due to increasing use of NFS over TCP - many
distros seem to be making it the default.

The SK_CONN bit gets set when a listening socket may be ready
for an accept, just as SK_DATA is set when data may be available.

It is entirely possible for svc_tcp_accept to be called with neither
of these set.  It doesn't happen often but there is a small race in
svc_sock_enqueue as SK_CONN and SK_DATA are tested outside the
spin_lock.  They could be cleared immediately after the test and
before the lock is gained.

This normally shouldn't be a problem.  The sockets are non-blocking so
trying to read() or accept() when ther is nothing to do is not a problem.

However: svc_tcp_recvfrom makes the decision "Should I accept() or
should I read()" based on whether SK_CONN is set or not.  This usually
works but is not safe.  The decision should be based on whether it is
a TCP_LISTEN socket or a TCP_CONNECTED socket.
Signed-off-by: NNeil Brown <neilb@suse.de>
Cc: Adrian Bunk <bunk@stusta.de>
Cc: <stable@kernel.org>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>