To avoid a lock inversion deadlock, the pty driver must distinguish when the flush_buffer() caller already holds its own tty_buffer buf->lock (currently only in N_TTY's receive_buf() path when handling signals).
Extend tty_driver ops interface with the flush_nested() method. Add the tty_driver_flush_nested() accessor which uses flush_nested() (if the driver declares it); otherwise, uses tty_driver_flush_buffer(). Signed-off-by: Peter Hurley <[email protected]> --- drivers/tty/n_tty.c | 4 ++-- drivers/tty/tty_ioctl.c | 21 +++++++++++++++++++++ include/linux/tty.h | 1 + include/linux/tty_driver.h | 1 + 4 files changed, 25 insertions(+), 2 deletions(-) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index bd01d97..72a5c32 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -1191,7 +1191,7 @@ static void n_tty_receive_break(struct tty_struct *tty) /* flushing needs exclusive termios_rwsem */ up_read(&tty->termios_rwsem); n_tty_flush_buffer(tty); - tty_driver_flush_buffer(tty); + tty_driver_flush_nested(tty); down_read(&tty->termios_rwsem); } return; @@ -1271,7 +1271,7 @@ n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c) /* flushing needs exclusive termios_rwsem */ up_read(&tty->termios_rwsem); n_tty_flush_buffer(tty); - tty_driver_flush_buffer(tty); + tty_driver_flush_nested(tty); down_read(&tty->termios_rwsem); } if (I_IXON(tty)) diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c index 6fd60fe..e64eb23 100644 --- a/drivers/tty/tty_ioctl.c +++ b/drivers/tty/tty_ioctl.c @@ -90,6 +90,27 @@ void tty_driver_flush_buffer(struct tty_struct *tty) EXPORT_SYMBOL(tty_driver_flush_buffer); /** + * tty_driver_flush_nested - discard internal buffer + * @tty: terminal + * + * Line disciplines must call this flavor of tty_driver_flush_buffer() + * if calling from their .receive_buf() method. The pty driver + * in particular requires special handling to avoid a lock inversion + * deadlock (see tty_buffer_flush_nested()). + * + * A normal flush_buffer() is performed for drivers without this + * extension. + */ +void tty_driver_flush_nested(struct tty_struct *tty) +{ + if (tty->ops->flush_nested) + tty->ops->flush_nested(tty); + else + tty_driver_flush_buffer(tty); +} +EXPORT_SYMBOL(tty_driver_flush_nested); + +/** * tty_throttle - flow control * @tty: terminal * diff --git a/include/linux/tty.h b/include/linux/tty.h index 9d234dc..de1f85f 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -414,6 +414,7 @@ extern int tty_put_char(struct tty_struct *tty, unsigned char c); extern int tty_chars_in_buffer(struct tty_struct *tty); extern int tty_write_room(struct tty_struct *tty); extern void tty_driver_flush_buffer(struct tty_struct *tty); +extern void tty_driver_flush_nested(struct tty_struct *tty); extern void tty_throttle(struct tty_struct *tty); extern void tty_unthrottle(struct tty_struct *tty); extern int tty_throttle_safe(struct tty_struct *tty); diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h index 756a609..4937e16 100644 --- a/include/linux/tty_driver.h +++ b/include/linux/tty_driver.h @@ -269,6 +269,7 @@ struct tty_operations { void (*hangup)(struct tty_struct *tty); int (*break_ctl)(struct tty_struct *tty, int state); void (*flush_buffer)(struct tty_struct *tty); + void (*flush_nested)(struct tty_struct *tty); void (*set_ldisc)(struct tty_struct *tty); void (*wait_until_sent)(struct tty_struct *tty, int timeout); void (*send_xchar)(struct tty_struct *tty, char ch); -- 1.8.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
