linux-kernel - [tip:sched/core] sched, tty: Deal with nested sleeps

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Message-ID: <tip-97d9e28d1a27b84a6a0b155f2390289afa279341@git.kernel.org>
Date:	Tue, 28 Oct 2014 04:10:52 -0700
From:	tip-bot for Peter Zijlstra <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	gregkh@...uxfoundation.org, peterz@...radead.org, jslaby@...e.cz,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	tglx@...utronix.de, hpa@...or.com, mingo@...nel.org
Subject: [tip:sched/core] sched, tty: Deal with nested sleeps

Commit-ID:  97d9e28d1a27b84a6a0b155f2390289afa279341
Gitweb:     http://git.kernel.org/tip/97d9e28d1a27b84a6a0b155f2390289afa279341
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Wed, 24 Sep 2014 10:18:51 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 28 Oct 2014 10:56:10 +0100

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: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jiri Slaby <jslaby@...e.cz>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: tglx@...utronix.de
Cc: ilya.dryomov@...tank.com
Cc: umgwanakikbuti@...il.com
Cc: oleg@...hat.com
Link: http://lkml.kernel.org/r/20140924082242.323011233@infradead.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 drivers/tty/n_tty.c | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 89c4cee..fb3f519 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -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);
--
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