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authorPeter Hurley <peter@hurleysoftware.com>2015-10-10 16:00:51 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-10-17 21:11:29 -0700
commit79c1faa4511e78380cd643dac88a775062a08bc0 (patch)
tree71d15bef9323d929a02d2f04d184ef2f7614b92e /drivers/tty/tty_port.c
parent32ede4a51754cb62b0d43d91cb7c4e3c57069a9c (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.c11
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)