From e359a4e38d229d53e28905863a1fabf41debd591 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Mon, 16 Jun 2014 09:17:06 -0400 Subject: 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 CC: Samuel Ortiz CC: "David S. Miller" Signed-off-by: Peter Hurley Acked-by: Jesper Nilsson Signed-off-by: Greg Kroah-Hartman --- drivers/char/pcmcia/synclink_cs.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/char') diff --git a/drivers/char/pcmcia/synclink_cs.c b/drivers/char/pcmcia/synclink_cs.c index 8320abd1ef14..a63970f76967 100644 --- a/drivers/char/pcmcia/synclink_cs.c +++ b/drivers/char/pcmcia/synclink_cs.c @@ -2510,7 +2510,7 @@ static int mgslpc_open(struct tty_struct *tty, struct file * filp) __FILE__, __LINE__, tty->driver->name, port->count); /* If port is closing, signal caller to try again */ - if (tty_hung_up_p(filp) || port->flags & ASYNC_CLOSING){ + if (port->flags & ASYNC_CLOSING){ wait_event_interruptible_tty(tty, port->close_wait, !(port->flags & ASYNC_CLOSING)); retval = ((port->flags & ASYNC_HUP_NOTIFY) ? -- cgit v1.2.3