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

tip-bot for Peter Zijlstra
2014-10-28T11:11:52Z

Commit-ID: 97d9e28d1a27b84a6a0b155f2390289afa279341
Gitweb: http://git.kernel.org/tip/97d9e28d1a27b84a6a0b155f2390289afa279341
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Wed, 24 Sep 2014 10:18:51 +0200
Committer: Ingo Molnar <mingo@kernel.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@infradead.org>
Acked-by: Greg 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: Ingo Molnar <mingo@kernel.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);