android_kernel_motorola_sm6225/net/rxrpc
Jiri Olsa a57de0b433 net: adding memory barrier to the poll and receive callbacks
Adding memory barrier after the poll_wait function, paired with
receive callbacks. Adding fuctions sock_poll_wait and sk_has_sleeper
to wrap the memory barrier.

Without the memory barrier, following race can happen.
The race fires, when following code paths meet, and the tp->rcv_nxt
and __add_wait_queue updates stay in CPU caches.

CPU1                         CPU2

sys_select                   receive packet
  ...                        ...
  __add_wait_queue           update tp->rcv_nxt
  ...                        ...
  tp->rcv_nxt check          sock_def_readable
  ...                        {
  schedule                      ...
                                if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
                                        wake_up_interruptible(sk->sk_sleep)
                                ...
                             }

If there was no cache the code would work ok, since the wait_queue and
rcv_nxt are opposit to each other.

Meaning that once tp->rcv_nxt is updated by CPU2, the CPU1 either already
passed the tp->rcv_nxt check and sleeps, or will get the new value for
tp->rcv_nxt and will return with new data mask.
In both cases the process (CPU1) is being added to the wait queue, so the
waitqueue_active (CPU2) call cannot miss and will wake up CPU1.

The bad case is when the __add_wait_queue changes done by CPU1 stay in its
cache, and so does the tp->rcv_nxt update on CPU2 side.  The CPU1 will then
endup calling schedule and sleep forever if there are no more data on the
socket.

Calls to poll_wait in following modules were ommited:
	net/bluetooth/af_bluetooth.c
	net/irda/af_irda.c
	net/irda/irnet/irnet_ppp.c
	net/mac80211/rc80211_pid_debugfs.c
	net/phonet/socket.c
	net/rds/af_rds.c
	net/rfkill/core.c
	net/sunrpc/cache.c
	net/sunrpc/rpc_pipe.c
	net/tipc/socket.c

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2009-07-09 17:06:57 -07:00
..
af_rxrpc.c net: adding memory barrier to the poll and receive callbacks 2009-07-09 17:06:57 -07:00
ar-accept.c net/rxrpc: Use an IS_ERR test rather than a NULL test 2008-08-13 02:40:48 -07:00
ar-ack.c net/rxrpc: Use BUG_ON 2008-02-17 18:42:03 -08:00
ar-call.c [AF_RXRPC]: constify function pointer tables 2008-01-31 19:27:18 -08:00
ar-connection.c RxRPC: Don't attempt to reuse aborted connections 2009-06-16 21:20:14 -07:00
ar-connevent.c RxRPC: Don't attempt to reuse aborted connections 2009-06-16 21:20:14 -07:00
ar-error.c net: replace NIPQUAD() in net/*/ 2008-10-31 00:54:56 -07:00
ar-input.c MIB: add struct net to UDP_INC_STATS_BH 2008-07-05 21:18:48 -07:00
ar-internal.h Merge branch 'master' of master.kernel.org:/pub/scm/linux/kernel/git/torvalds/linux-2.6 2008-04-17 23:56:30 -07:00
ar-key.c CRED: Inaugurate COW credentials 2008-11-14 10:39:23 +11:00
ar-local.c net: replace NIPQUAD() in net/*/ 2008-10-31 00:54:56 -07:00
ar-output.c [AF_RXRPC]: Return the number of bytes buffered in rxrpc_send_data() 2007-06-18 23:30:41 -07:00
ar-peer.c net: replace NIPQUAD() in net/*/ 2008-10-31 00:54:56 -07:00
ar-proc.c net: replace NIPQUAD() in net/*/ 2008-10-31 00:54:56 -07:00
ar-recvmsg.c RxRPC: fix rxrpc_recvmsg()'s returning of msg_name 2008-03-05 18:53:55 -08:00
ar-security.c net: Make static 2008-12-10 15:18:31 -08:00
ar-skbuff.c [AF_RXRPC]: Add an interface to the AF_RXRPC module for the AFS filesystem to use 2007-04-26 15:50:17 -07:00
ar-transport.c net: replace NIPQUAD() in net/*/ 2008-10-31 00:54:56 -07:00
Kconfig [RXRPC]: Add missing select on CRYPTO 2007-11-30 23:30:40 +11:00
Makefile [AF_RXRPC]: Delete the old RxRPC code. 2007-04-26 15:55:48 -07:00
rxkad.c net: replace NIPQUAD() in net/*/ 2008-10-31 00:54:56 -07:00