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/serial/crisv10.c b/drivers/tty/serial/crisv10.c
index d567ac5..58e6f61 100644
--- a/drivers/tty/serial/crisv10.c
+++ b/drivers/tty/serial/crisv10.c
@@ -3831,14 +3831,13 @@
DECLARE_WAITQUEUE(wait, current);
unsigned long flags;
int retval;
- int do_clocal = 0, extra_count = 0;
+ int do_clocal = 0;
/*
* If the device is in the middle of being closed, then block
* until it's done, and then 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));
#ifdef SERIAL_DO_RESTART
@@ -3879,10 +3878,7 @@
info->line, info->port.count);
#endif
local_irq_save(flags);
- if (!tty_hung_up_p(filp)) {
- extra_count++;
- info->port.count--;
- }
+ info->port.count--;
local_irq_restore(flags);
info->port.blocked_open++;
while (1) {
@@ -3921,7 +3917,7 @@
}
set_current_state(TASK_RUNNING);
remove_wait_queue(&info->port.open_wait, &wait);
- if (extra_count)
+ if (!tty_hung_up_p(filp))
info->port.count++;
info->port.blocked_open--;
#ifdef SERIAL_DEBUG_OPEN
@@ -3976,8 +3972,7 @@
/*
* If the port is in the middle of closing, bail out now
*/
- 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));
#ifdef SERIAL_DO_RESTART