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sched, tty: Deal with nested sleeps

Browse source 
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) <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Peter Zijlstra 2014-09-24 10:18:51 +02:00 • committed by Ingo Molnar
commit 97d9e28d1a
1 changed files with 5 additions and 12 deletions
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17
drivers/tty/n_tty.c
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@ -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);