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From: Arnd Bergmann on 30 Mar 2010 17:00
This is one of the tricker bits in the BKL removal series,
so let's discuss it here. In order to build a kernel without
the BKL, it's obviously necessary to do something about
the TTY code. This series introduces a new Big TTY Mutex
that is based on the earlier implementation of the
Big Kernel Semaphore, but comes with a number of changes:

- based on the mutex code instead of a semaphore,
so we can use all the mutex debugging.
- no autorelease on sleep, which is what most of the
series is about.
- limited to one subsystem only.
- ability to annotate nested locking so we can eventually
turn it into a non-recursive mutex, once all the
recursive users stay around.

The first eight patches convert all the code using the BKL
in the TTY layer and related drivers to the new interface,
while the final patch adds the real mutex implementation
as an experimental configuration option.

When that option is disabled, the behaviour should be
basically unchanged regarding serialization against
other subsystems using the BKL.

Together with the patches removing the BKL from block,
procfs, init, usb and VFS, it then becomes realistic to
build a kernel that does not contain the BKL at all,
while disabling all code that still uses it.
This means we are still safe, because there is no code
left that the new BTM fails to serialize with.

This smaller series is taken from my bkl-removal tree,
ported to 2.6.34-rc3 and with the last patch changed to
make the new implementation optional.

Arnd
---

Arnd Bergmann (9):
tty: replace BKL with a new tty_lock
tty: make atomic_write_lock release tty_lock
tty: make tty_port->mutex nest under tty_lock
tty: make termios mutex nest under tty_lock
tty: make ldisc_mutex nest under tty_lock
tty: never hold tty_lock() while getting tty_mutex
ppp: use big tty mutex
tty: release tty lock when blocking
tty: implement BTM as mutex instead of BKL

drivers/char/Makefile | 1 +
drivers/char/amiserial.c | 16 ++--
drivers/char/briq_panel.c | 6 +-
drivers/char/cyclades.c | 20 ++--
drivers/char/epca.c | 4 +-
drivers/char/isicom.c | 10 +-
drivers/char/istallion.c | 20 ++--
drivers/char/mxser.c | 10 +-
drivers/char/n_hdlc.c | 16 ++--
drivers/char/n_r3964.c | 10 +-
drivers/char/pty.c | 8 +-
drivers/char/riscom8.c | 8 +-
drivers/char/rocket.c | 8 +-
drivers/char/serial167.c | 4 +-
drivers/char/specialix.c | 10 +-
drivers/char/stallion.c | 12 ++--
drivers/char/sx.c | 12 ++--
drivers/char/synclink.c | 10 ++-
drivers/char/synclink_gt.c | 8 +-
drivers/char/synclinkmp.c | 12 ++--
drivers/char/tty_buffer.c | 2 +-
drivers/char/tty_io.c | 123 ++++++++++++++-----------
drivers/char/tty_ioctl.c | 36 ++++----
drivers/char/tty_ldisc.c | 53 +++++++-----
drivers/char/tty_port.c | 6 +-
drivers/char/vc_screen.c | 4 +-
drivers/char/vt.c | 4 +-
drivers/char/vt_ioctl.c | 12 ++--
drivers/isdn/i4l/isdn_common.c | 20 ++--
drivers/isdn/i4l/isdn_tty.c | 8 +-
drivers/net/irda/irtty-sir.c | 5 +-
drivers/net/ppp_generic.c | 29 +++---
drivers/serial/68360serial.c | 4 +-
drivers/serial/crisv10.c | 8 +-
drivers/serial/serial_core.c | 42 +++++-----
drivers/staging/strip/strip.c | 2 +-
drivers/usb/class/cdc-acm.c | 2 +-
drivers/usb/serial/usb-serial.c | 18 ++--
drivers/video/console/vgacon.c | 4 +-
include/linux/init_task.h | 1 +
include/linux/sched.h | 1 +
include/linux/tty.h | 188 +++++++++++++++++++++++++++++++++++++++
kernel/fork.c | 1 +
lib/Kconfig.debug | 10 ++
44 files changed, 510 insertions(+), 278 deletions(-)

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