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Commit 97d9e28d authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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sched, tty: Deal with nested sleeps 



n_tty_{read,write} are wait loops with sleeps in. Wait loops rely on
task_struct::state and sleeps do too, since that's the only means of
actually sleeping. Therefore the nested sleeps destroy the wait loop
state.

Fix this by using the new woken_wake_function and wait_woken() stuff,
which registers wakeups in wait and thereby allows shrinking the
task_state::state changes to the actual sleep part.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: tglx@linutronix.de
Cc: ilya.dryomov@inktank.com
Cc: umgwanakikbuti@gmail.com
Cc: oleg@redhat.com
Link: http://lkml.kernel.org/r/20140924082242.323011233@infradead.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent e23738a7

drivers/tty/n_tty.c

+5 −12
Original line number Diff line number Diff line
@@ -2123,7 +2123,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, 
{

	struct n_tty_data *ldata = tty->disc_data;

	unsigned char __user *b = buf;

	DECLARE_WAITQUEUE(wait, current);

	DEFINE_WAIT_FUNC(wait, woken_wake_function);

	int c;

	int minimum, time;

	ssize_t retval = 0;
@@ -2186,10 +2186,6 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, 
			nr--;

			break;

		}

		/* This statement must be first before checking for input

		   so that any interrupt will set the state back to

		   TASK_RUNNING. */

		set_current_state(TASK_INTERRUPTIBLE);



		if (((minimum - (b - buf)) < ldata->minimum_to_wake) &&

		    ((minimum - (b - buf)) >= 1))
@@ -2220,13 +2216,13 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, 
				n_tty_set_room(tty);

				up_read(&tty->termios_rwsem);



				timeout = schedule_timeout(timeout);

				timeout = wait_woken(&wait, TASK_INTERRUPTIBLE,

						     timeout);



				down_read(&tty->termios_rwsem);

				continue;

			}

		}

		__set_current_state(TASK_RUNNING);



		/* Deal with packet mode. */

		if (packet && b == buf) {
@@ -2273,7 +2269,6 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, 


	mutex_unlock(&ldata->atomic_read_lock);



	__set_current_state(TASK_RUNNING);

	if (b - buf)

		retval = b - buf;
@@ -2306,7 +2301,7 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file, 
			   const unsigned char *buf, size_t nr)

{

	const unsigned char *b = buf;

	DECLARE_WAITQUEUE(wait, current);

	DEFINE_WAIT_FUNC(wait, woken_wake_function);

	int c;

	ssize_t retval = 0;
@@ -2324,7 +2319,6 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file, 


	add_wait_queue(&tty->write_wait, &wait);

	while (1) {

		set_current_state(TASK_INTERRUPTIBLE);

		if (signal_pending(current)) {

			retval = -ERESTARTSYS;

			break;
@@ -2378,12 +2372,11 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file, 
		}

		up_read(&tty->termios_rwsem);



		schedule();

		wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);



		down_read(&tty->termios_rwsem);

	}

break_out:

	__set_current_state(TASK_RUNNING);

	remove_wait_queue(&tty->write_wait, &wait);

	if (b - buf != nr && tty->fasync)

		set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);