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 commita57a7bf3fc
("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 commit0911261d4c
("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>
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@ -1582,7 +1582,7 @@ isdn_tty_close(struct tty_struct *tty, struct file *filp)
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* line status register.
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*/
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if (port->flags & ASYNC_INITIALIZED) {
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tty_wait_until_sent_from_close(tty, 3000); /* 30 seconds timeout */
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tty_wait_until_sent(tty, 3000); /* 30 seconds timeout */
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/*
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* Before we drop DTR, make sure the UART transmitter
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* has completely drained; this is especially
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@ -418,7 +418,7 @@ static void hvc_close(struct tty_struct *tty, struct file * filp)
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* there is no buffered data otherwise sleeps on a wait queue
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* waking periodically to check chars_in_buffer().
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*/
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tty_wait_until_sent_from_close(tty, HVC_CLOSE_WAIT);
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tty_wait_until_sent(tty, HVC_CLOSE_WAIT);
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} else {
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if (hp->port.count < 0)
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printk(KERN_ERR "hvc_close %X: oops, count is %d\n",
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@ -1230,7 +1230,7 @@ static void hvcs_close(struct tty_struct *tty, struct file *filp)
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irq = hvcsd->vdev->irq;
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spin_unlock_irqrestore(&hvcsd->lock, flags);
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tty_wait_until_sent_from_close(tty, HVCS_CLOSE_WAIT);
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tty_wait_until_sent(tty, HVCS_CLOSE_WAIT);
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/*
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* This line is important because it tells hvcs_open that this
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@ -463,10 +463,7 @@ static void tty_port_drain_delay(struct tty_port *port, struct tty_struct *tty)
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schedule_timeout_interruptible(timeout);
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}
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/* Caller holds tty lock.
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* NB: may drop and reacquire tty lock (in tty_wait_until_sent_from_close())
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* so tty and tty port may have changed state (but not hung up or reopened).
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*/
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/* Caller holds tty lock. */
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int tty_port_close_start(struct tty_port *port,
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struct tty_struct *tty, struct file *filp)
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{
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@ -502,7 +499,7 @@ int tty_port_close_start(struct tty_port *port,
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if (tty->flow_stopped)
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tty_driver_flush_buffer(tty);
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if (port->closing_wait != ASYNC_CLOSING_WAIT_NONE)
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tty_wait_until_sent_from_close(tty, port->closing_wait);
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tty_wait_until_sent(tty, port->closing_wait);
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if (port->drain_delay)
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tty_port_drain_delay(port, tty);
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}
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@ -543,10 +540,6 @@ EXPORT_SYMBOL(tty_port_close_end);
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* tty_port_close
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*
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* Caller holds tty lock
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*
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* NB: may drop and reacquire tty lock (in tty_port_close_start()->
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* tty_wait_until_sent_from_close()) so tty and tty_port may have changed
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* state (but not hung up or reopened).
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*/
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void tty_port_close(struct tty_port *port, struct tty_struct *tty,
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struct file *filp)
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@ -656,24 +656,6 @@ extern void __lockfunc tty_unlock(struct tty_struct *tty);
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extern void __lockfunc tty_lock_slave(struct tty_struct *tty);
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extern void __lockfunc tty_unlock_slave(struct tty_struct *tty);
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extern void tty_set_lock_subclass(struct tty_struct *tty);
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/*
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* this shall be called only from where BTM is held (like close)
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*
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* We need this to ensure nobody waits for us to finish while we are waiting.
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* Without this we were encountering system stalls.
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*
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* This should be indeed removed with BTM removal later.
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*
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* Locking: BTM required. Nobody is allowed to hold port->mutex.
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*/
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static inline void tty_wait_until_sent_from_close(struct tty_struct *tty,
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long timeout)
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{
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tty_unlock(tty); /* tty->ops->close holds the BTM, drop it while waiting */
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tty_wait_until_sent(tty, timeout);
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tty_lock(tty);
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}
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/*
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* wait_event_interruptible_tty -- wait for a condition with the tty lock held
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*
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