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>

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 89c4cee253e34419006b670089cc54b0257dde52..fb3f519b803f451ac77b38b00e8d3df04f078e0b 100644 (file)
--- 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);