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author | Peter Hurley <peter@hurleysoftware.com> | 2014-06-16 09:17:06 -0400 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-07-10 16:06:49 -0700 |
commit | e359a4e38d229d53e28905863a1fabf41debd591 (patch) | |
tree | c70f7762dac31dad62188b7b8bb2140bea8b311a /drivers/tty/tty_port.c | |
parent | 5fda7a0e715c32c6dd9a39ebce8429eeafb64b7d (diff) | |
download | linux-e359a4e38d229d53e28905863a1fabf41debd591.tar.gz linux-e359a4e38d229d53e28905863a1fabf41debd591.tar.bz2 linux-e359a4e38d229d53e28905863a1fabf41debd591.zip |
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.c | 8 |
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); |