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 --- net/irda/ircomm/ircomm_tty.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) (limited to 'net') diff --git a/net/irda/ircomm/ircomm_tty.c b/net/irda/ircomm/ircomm_tty.c index 2ba8b9705bb7..61ceb4cdb4a2 100644 --- a/net/irda/ircomm/ircomm_tty.c +++ b/net/irda/ircomm/ircomm_tty.c @@ -320,8 +320,7 @@ static int ircomm_tty_block_til_ready(struct ircomm_tty_cb *self, __FILE__, __LINE__, tty->driver->name, port->count); spin_lock_irqsave(&port->lock, flags); - if (!tty_hung_up_p(filp)) - port->count--; + port->count--; port->blocked_open++; spin_unlock_irqrestore(&port->lock, flags); @@ -458,8 +457,7 @@ static int ircomm_tty_open(struct tty_struct *tty, struct file *filp) /* * If the port is the middle of closing, bail out now */ - if (tty_hung_up_p(filp) || - test_bit(ASYNCB_CLOSING, &self->port.flags)) { + if (test_bit(ASYNCB_CLOSING, &self->port.flags)) { /* Hm, why are we blocking on ASYNC_CLOSING if we * do return -EAGAIN/-ERESTARTSYS below anyway? -- cgit v1.2.3