linux-sg2042/net/irda/ircomm
Peter Hurley e359a4e38d tty: Remove tty_hung_up_p() tests from tty drivers' open()
Since at least before 2.6.30, it has not been possible to observe
a hung up file pointer in a tty driver's open() method unless/until
the driver open() releases the tty_lock() (eg., before blocking).

This is because tty_open() adds the file pointer while holding
the tty_lock() _and_ doesn't release the lock until after calling
the tty driver's open() method. [ Before tty_lock(), this was
lock_kernel(). ]

Since __tty_hangup() first waits on the tty_lock() before
enumerating and hanging up the open file pointers, either
__tty_hangup() will wait for the tty_lock() or tty_open() will
not yet have added the file pointer. For example,

CPU 0                          |  CPU 1
                               |
tty_open                       |  __tty_hangup
  ..                           |    ..
  tty_lock                     |    ..
  tty_reopen                   |    tty_lock  / blocks
  ..                           |
  tty_add_file(tty, filp)      |
  ..                           |
  tty->ops->open(tty, filp)    |
    tty_port_open              |
      tty_port_block_til_ready |
        ..                     |
        while (1)              |
          ..                   |
          tty_unlock           |    / unblocks
          schedule             |    for each filp on tty->tty_files
                               |      f_ops = tty_hung_up_fops;
                               |    ..
                               |    tty_unlock
          tty_lock             |
  ..                           |
  tty_unlock                   |

Note that since tty_port_block_til_ready() and similar drop
the tty_lock while blocking, when woken, the file pointer
must then be tested for having been hung up.

Also, fix bit-rotted drivers that used extra_count to track the
port->count bump.

CC: Mikael Starvik <starvik@axis.com>
CC: Samuel Ortiz <samuel@sortiz.org>
CC: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Jesper Nilsson <jesper.nilsson@axis.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2014-07-10 16:06:49 -07:00
..
Kconfig tty: Added a CONFIG_TTY option to allow removal of TTY 2013-01-18 16:15:27 -08:00
Makefile Net: irda: ircomm: Makefile: Remove deprecated kbuild goal defintions 2010-11-22 08:16:12 -08:00
ircomm_core.c net/irda: Fix FSF address in file headers 2013-12-06 12:37:57 -05:00
ircomm_event.c net/irda: Fix FSF address in file headers 2013-12-06 12:37:57 -05:00
ircomm_lmp.c net/irda: Fix FSF address in file headers 2013-12-06 12:37:57 -05:00
ircomm_param.c net/irda: Fix FSF address in file headers 2013-12-06 12:37:57 -05:00
ircomm_ttp.c net/irda: Fix FSF address in file headers 2013-12-06 12:37:57 -05:00
ircomm_tty.c tty: Remove tty_hung_up_p() tests from tty drivers' open() 2014-07-10 16:06:49 -07:00
ircomm_tty_attach.c net/irda: Fix FSF address in file headers 2013-12-06 12:37:57 -05:00
ircomm_tty_ioctl.c net/irda: Fix FSF address in file headers 2013-12-06 12:37:57 -05:00