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>
diff --git a/drivers/tty/synclink_gt.c b/drivers/tty/synclink_gt.c
index c359a91..ba1dbcd 100644
--- a/drivers/tty/synclink_gt.c
+++ b/drivers/tty/synclink_gt.c
@@ -673,7 +673,7 @@
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 @@
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 @@
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 @@
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--;