tty_perform_flush() can deadlock when called while holding
a line discipline reference. By definition, all ldisc drivers
hold a ldisc reference, so calls originating from ldisc drivers
must not block for a ldisc reference.

The deadlock can occur when:
  CPU 0                    |  CPU 1
                           |
tty_ldisc_ref(tty)         |
....                       | <line discipline halted>
tty_ldisc_ref_wait(tty)    |
                           |

CPU 0 cannot progess because it cannot obtain an ldisc reference
with the line discipline has been halted (thus no new references
are granted).
CPU 1 cannot progress because an outstanding ldisc reference
has not been released.

An in-tree call-tree audit of tty_perform_flush() [1] shows 5
ldisc drivers calling tty_perform_flush() indirectly via
n_tty_ioctl_helper() and 2 ldisc drivers calling directly.
A single tty driver safely uses the function.

[1]
Recursive usage:

/* These functions are line discipline ioctls and thus
 * recursive wrt line discipline references */

tty_perform_flush() - ./drivers/tty/tty_ioctl.c
    n_tty_ioctl_helper()
        hci_uart_tty_ioctl(default) - drivers/bluetooth/hci_ldisc.c (N_HCI)
        n_hdlc_tty_ioctl(default) - drivers/tty/n_hdlc.c (N_HDLC)
        gsmld_ioctl(default) - drivers/tty/n_gsm.c (N_GSM0710)
        n_tty_ioctl(default) - drivers/tty/n_tty.c (N_TTY)
        gigaset_tty_ioctl(default) - drivers/isdn/gigaset/ser-gigaset.c (N_GIGASET_M101)
    ppp_synctty_ioctl(TCFLSH) - drivers/net/ppp/pps_synctty.c
    ppp_asynctty_ioctl(TCFLSH) - drivers/net/ppp/ppp_async.c

Non-recursive use:

tty_perform_flush() - drivers/tty/tty_ioctl.c
    ipw_ioctl(TCFLSH) - drivers/tty/ipwireless/tty.c
       /* This function is a tty i/o ioctl method, which
        * is invoked by tty_ioctl() */

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Call consume_skb() in place of kfree_skb() were appropriate.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Since all that include/linux/if_ppp.h does is #include <linux/ppp-ioctl.h>,
this replaces the occurrences of #include <linux/if_ppp.h> with
#include <linux/ppp-ioctl.h>.

It also corrects an error in Documentation/networking/l2tp.txt, where
it referenced include/linux/if_ppp.h as the source of some definitions
that are actually now defined in include/linux/if_pppol2tp.h.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Move the PPP drivers into drivers/net/ppp/ and make the
necessary Kconfig and Makefile changes.

CC: Paul Mackerras <paulus@samba.org>
CC: Frank Cusack <fcusack@fcusack.com>
CC: Michal Ostrowski <mostrows@speakeasy.net>
CC: Michal Ostrowski <mostrows@earthlink.net>
CC: Dmitry Kozlov <xeb@mail.ru>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>