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authorPeter Hurley <peter@hurleysoftware.com>2014-06-16 09:17:06 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-07-10 16:06:49 -0700
commite359a4e38d229d53e28905863a1fabf41debd591 (patch)
treec70f7762dac31dad62188b7b8bb2140bea8b311a /drivers/tty/tty_port.c
parent5fda7a0e715c32c6dd9a39ebce8429eeafb64b7d (diff)
downloadlinux-e359a4e38d229d53e28905863a1fabf41debd591.tar.bz2
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>
Diffstat (limited to 'drivers/tty/tty_port.c')
-rw-r--r--drivers/tty/tty_port.c8
1 files changed, 3 insertions, 5 deletions
diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
index 9209d6331b8e..1b9335796da4 100644
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -365,7 +365,7 @@ int tty_port_block_til_ready(struct tty_port *port,
DEFINE_WAIT(wait);
/* block if port is in the process of being closed */
- 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));
if (port->flags & ASYNC_HUP_NOTIFY)
@@ -399,8 +399,7 @@ int tty_port_block_til_ready(struct tty_port *port,
/* The port lock protects the port counts */
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);
@@ -593,8 +592,7 @@ int tty_port_open(struct tty_port *port, struct tty_struct *tty,
struct file *filp)
{
spin_lock_irq(&port->lock);
- if (!tty_hung_up_p(filp))
- ++port->count;
+ ++port->count;
spin_unlock_irq(&port->lock);
tty_port_tty_set(port, tty);