diff options
| author | Peter Hurley <peter@hurleysoftware.com> | 2015-10-10 16:00:51 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-10-17 21:11:29 -0700 |
| commit | 79c1faa4511e78380cd643dac88a775062a08bc0 (patch) | |
| tree | 71d15bef9323d929a02d2f04d184ef2f7614b92e /drivers/tty/tty_port.c | |
| parent | 32ede4a51754cb62b0d43d91cb7c4e3c57069a9c (diff) | |
tty: Remove tty_wait_until_sent_from_close()
tty_wait_until_sent_from_close() drops the tty lock while waiting
for the tty driver to finish sending previously accepted data (ie.,
data remaining in its write buffer and transmit fifo).
tty_wait_until_sent_from_close() was added by commit a57a7bf3fc7e
("TTY: define tty_wait_until_sent_from_close") to prevent the entire
tty subsystem from being unable to open new ttys while waiting for
one tty to close while output drained.
However, since commit 0911261d4cb6 ("tty: Don't take tty_mutex for tty
count changes"), holding a tty lock while closing does not prevent other
ttys from being opened/closed/hung up, but only prevents lifetime event
changes for the tty under lock.
Holding the tty lock while waiting for output to drain does prevent
parallel non-blocking opens (O_NONBLOCK) from advancing or returning
while the tty lock is held. However, all parallel opens _already_
block even if the tty lock is dropped while closing and the parallel
open advances. Blocking in open has been in mainline since at least 2.6.29
(see tty_port_block_til_ready(); note the test for O_NONBLOCK is _after_
the wait while ASYNC_CLOSING).
IOW, before this patch a non-blocking open will sleep anyway for the
_entire_ duration of a parallel hardware shutdown, and when it wakes, the
error return will cause a release of its tty, and it will restart with
a fresh attempt to open. Similarly with a blocking open that is already
waiting; when it's woken, the hardware shutdown has already completed
to ASYNC_INITIALIZED is not set, which forces a release and restart as
well.
So, holding the tty lock across the _entire_ close (which is what this
patch does), even while waiting for output to drain, is equivalent to
the current outcome wrt parallel opens.
Cc: Alan Cox <alan@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
CC: Arnd Bergmann <arnd@arndb.de>
CC: Karsten Keil <isdn@linux-pingi.de>
CC: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Peter Hurley <peter@hurleysoftware.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 | 11 |
1 files changed, 2 insertions, 9 deletions
diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c index 40b31835f80b..d7d9f9cde964 100644 --- a/drivers/tty/tty_port.c +++ b/drivers/tty/tty_port.c @@ -463,10 +463,7 @@ static void tty_port_drain_delay(struct tty_port *port, struct tty_struct *tty) schedule_timeout_interruptible(timeout); } -/* Caller holds tty lock. - * NB: may drop and reacquire tty lock (in tty_wait_until_sent_from_close()) - * so tty and tty port may have changed state (but not hung up or reopened). - */ +/* Caller holds tty lock. */ int tty_port_close_start(struct tty_port *port, struct tty_struct *tty, struct file *filp) { @@ -502,7 +499,7 @@ int tty_port_close_start(struct tty_port *port, if (tty->flow_stopped) tty_driver_flush_buffer(tty); if (port->closing_wait != ASYNC_CLOSING_WAIT_NONE) - tty_wait_until_sent_from_close(tty, port->closing_wait); + tty_wait_until_sent(tty, port->closing_wait); if (port->drain_delay) tty_port_drain_delay(port, tty); } @@ -543,10 +540,6 @@ EXPORT_SYMBOL(tty_port_close_end); * tty_port_close * * Caller holds tty lock - * - * NB: may drop and reacquire tty lock (in tty_port_close_start()-> - * tty_wait_until_sent_from_close()) so tty and tty_port may have changed - * state (but not hung up or reopened). */ void tty_port_close(struct tty_port *port, struct tty_struct *tty, struct file *filp) |