From: Tyler Hall <tylerwh...@gmail.com> Date: Sun, 15 Jun 2014 22:23:16 -0400
> Use schedule_work() to avoid potentially taking the spinlock in > interrupt context. > > Commit cc9fa74e2a ("slip/slcan: added locking in wakeup function") added > necessary locking to the wakeup function and 367525c8c2/ddcde142be ("can: > slcan: Fix spinlock variant") converted it to spin_lock_bh() because the lock > is also taken in timers. > > Disabling softirqs is not sufficient, however, as tty drivers may call > write_wakeup from interrupt context. This driver calls tty->ops->write() with > its spinlock held, which may immediately cause an interrupt on the same CPU > and > subsequent spin_bug(). > > Simply converting to spin_lock_irq/irqsave() prevents this deadlock, but > causes lockdep to point out a possible circular locking dependency > between these locks: > > (&(&sl->lock)->rlock){-.....}, at: slip_write_wakeup > (&port_lock_key){-.....}, at: serial8250_handle_irq.part.13 > > The slip transmit is holding the slip spinlock when calling the tty write. > This grabs the port lock. On an interrupt, the handler grabs the port > lock and calls write_wakeup which grabs the slip lock. This could be a > problem if a serial interrupt occurs on another CPU during the slip > transmit. > > To deal with these issues, don't grab the lock in the wakeup function by > deferring the writeout to a workqueue. Also hold the lock during close > when de-assigning the tty pointer to safely disarm the worker and > timers. > > This bug is easily reproducible on the first transmit when slip is > used with the standard 8250 serial driver. ... > Signed-off-by: Tyler Hall <tylerwh...@gmail.com> Applied and queued up for -stable. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/