Commit acfa747b introduced the TTY_HUPPING flag to distinguish
closed TTY from currently closing ones. The test in tty_set_ldisc
still remained pointing at the old flag. This causes pppd to
sometimes lapse into uninterruptible sleep when killed and
restarted.

Signed-off-by: Shachar Shemesh <shachar@liveu.tv>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This reverts the tty layer change to use per-tty locking, because it's
not correct yet, and fixing it will require some more deep surgery.

The main revert is d29f3ef39be4 ("tty_lock: Localise the lock"), but
there are several smaller commits that built upon it, they also get
reverted here. The list of reverted commits is:

  fde86d310886 - tty: add lockdep annotations
  8f6576ad476b - tty: fix ldisc lock inversion trace
  d3ca8b64b97e - pty: Fix lock inversion
  b1d679afd766 - tty: drop the pty lock during hangup
  abcefe5fc357 - tty/amiserial: Add missing argument for tty_unlock()
  fd11b42e3598 - cris: fix missing tty arg in wait_event_interruptible_tty call
  d29f3ef39be4 - tty_lock: Localise the lock

The revert had a trivial conflict in the 68360serial.c staging driver
that got removed in the meantime.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

This is caused by tty_release using tty_lock_pair to lock both sides of
the pty/tty pair, and then tty_ldisc_release dropping and relocking one
side only.  We can drop both fine, so drop both to avoid any lock
ordering concerns.

Rework the release path to fix the new locking model.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

The global wait_queue that is used for line discipline idle handling is
moved to a separate wait_queue for each line instance. This prevents
unnecessary blocking on one line, because of idle handling on another
line.

Signed-off-by: Ivo Sieben <meltedpianoman@gmail.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

In each remaining case the tty_lock is associated with a specific tty. This
means we can now lock on a per tty basis. We do need tty_lock_pair() for
the pty case. Uglier but still a step in the right direction.

[fixed up calls in 3 missing drivers - gregkh]

Signed-off-by: Alan Cox <alan@linux.intel.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

They were cut&pasted from tty_io. Many of them are not needed in
tty_ldisc.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

For /dev/console case, we do not kill all ldisc users. It's due to
redirected_tty_write test in __tty_hangup. In that case there still
might be a process waiting e.g. in n_tty_read for input.

We wait for such processes to disappear. The problem is that we use a
timeout. After this timeout, we continue closing the ldisc and start
freeing tty resources. It obviously leads to crashes when the other
process is woken.

So to fix this, we wait infinitely before reiniting the ldisc. (The
tiocsetd remains untouched -- times out after 5s.)

This is nicely reproducible with this run from shell:
  exec 0<>/dev/console 1<>/dev/console 2<>/dev/console
and stopping a getty like:
  systemctl stop serial-getty@ttyS0.service

The crash proper may be produced only under load or with constified
timing the same as for 92f6fa09b.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Dave Young <hidave.darkstar@gmail.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Dmitriy Matrosov <sgf.dma@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

It is the only place where reinit is called from. And we really need
to wait for the old ldisc to go once. Actually this is the place where
the waiting originally was (before removed and re-added later).

This will make the fix in the following patch easier to implement.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Dave Young <hidave.darkstar@gmail.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Dmitriy Matrosov <sgf.dma@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

To fix a nasty bug in ldisc hup vs. reinit we need to wait infinitely
long for ldisc to be gone. So here we add a parameter to
tty_ldisc_wait_idle to allow that.

This is only a preparation for the real fix which is done in the
following patches.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Dave Young <hidave.darkstar@gmail.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Dmitriy Matrosov <sgf.dma@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>