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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/synclink_gt.c
parent5fda7a0e715c32c6dd9a39ebce8429eeafb64b7d (diff)
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/synclink_gt.c')
-rw-r--r--drivers/tty/synclink_gt.c10
1 files changed, 3 insertions, 7 deletions
diff --git a/drivers/tty/synclink_gt.c b/drivers/tty/synclink_gt.c
index c359a91f7346..ba1dbcdf4609 100644
--- a/drivers/tty/synclink_gt.c
+++ b/drivers/tty/synclink_gt.c
@@ -673,7 +673,7 @@ static int open(struct tty_struct *tty, struct file *filp)
DBGINFO(("%s open, old ref count = %d\n", info->device_name, info->port.count));
/* If port is closing, signal caller to try again */
- if (tty_hung_up_p(filp) || info->port.flags & ASYNC_CLOSING){
+ if (info->port.flags & ASYNC_CLOSING){
wait_event_interruptible_tty(tty, info->port.close_wait,
!(info->port.flags & ASYNC_CLOSING));
retval = ((info->port.flags & ASYNC_HUP_NOTIFY) ?
@@ -3273,7 +3273,6 @@ static int block_til_ready(struct tty_struct *tty, struct file *filp,
DECLARE_WAITQUEUE(wait, current);
int retval;
bool do_clocal = false;
- bool extra_count = false;
unsigned long flags;
int cd;
struct tty_port *port = &info->port;
@@ -3300,10 +3299,7 @@ static int block_til_ready(struct tty_struct *tty, struct file *filp,
add_wait_queue(&port->open_wait, &wait);
spin_lock_irqsave(&info->lock, flags);
- if (!tty_hung_up_p(filp)) {
- extra_count = true;
- port->count--;
- }
+ port->count--;
spin_unlock_irqrestore(&info->lock, flags);
port->blocked_open++;
@@ -3338,7 +3334,7 @@ static int block_til_ready(struct tty_struct *tty, struct file *filp,
set_current_state(TASK_RUNNING);
remove_wait_queue(&port->open_wait, &wait);
- if (extra_count)
+ if (!tty_hung_up_p(filp))
port->count++;
port->blocked_open--;