Messages in this thread Patch in this message | | | Date | Wed, 24 Sep 2014 10:18:51 +0200 | From | Peter Zijlstra <> | Subject | [PATCH 06/11] tty: Deal with nested sleeps |
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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.
Cc: Jiri Slaby <jslaby@suse.cz> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- drivers/tty/n_tty.c | 17 +++++------------ 1 file changed, 5 insertions(+), 12 deletions(-)
--- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -2123,7 +2123,7 @@ static ssize_t n_tty_read(struct tty_str { 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_str 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_str 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_str 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_st 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_st 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_st } 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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