Hi Josef, On 03/01/2016 10:02 AM, Josef Bacik wrote: > We hit a panic pretty consistently in production that looked like this > > PID: 461061 TASK: ffff880203f8bc00 CPU: 2 COMMAND: "kworker/u8:2" > #0 [ffff88015834b940] machine_kexec at ffffffff8103c1c5 > #1 [ffff88015834b990] crash_kexec at ffffffff810cd448 > #2 [ffff88015834ba60] oops_end at ffffffff81006478 > #3 [ffff88015834ba90] no_context at ffffffff818c5262 > #4 [ffff88015834baf0] __bad_area_nosemaphore at ffffffff818c545a > #5 [ffff88015834bb40] bad_area_nosemaphore at ffffffff818c548c > #6 [ffff88015834bb50] __do_page_fault at ffffffff81045ad5 > #7 [ffff88015834bbc0] do_page_fault at ffffffff81045efc > #8 [ffff88015834bbd0] page_fault at ffffffff818d6b82 > [exception RIP: __uart_start+0x1a] > RIP: ffffffff8152f30a RSP: ffff88015834bc80 RFLAGS: 00010046 > RAX: 0000000000000000 RBX: ffffffff822e9920 RCX: 0000000000000036 > RDX: 0000000000003636 RSI: 00000000000000fe RDI: ffffffff822e9920 > RBP: ffff88015834bca8 R8: 0000000000000000 R9: 00000000ffffffff > R10: ffff8802546f0d20 R11: 0000000000000000 R12: ffff880254712400 > R13: 0000000000000286 R14: 00000000000000fe R15: ffff880254712400 > ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018 > #9 [ffff88015834bc80] uart_start at ffffffff8152fbf2 Thanks for the report, but where's the rest of the stack trace? > It was a NULL pointer dereference, the state->port.tty was NULL so when we go to > check tty->stopped in uart_tx_stopped() we panic. Looking at the other CPU's we > were in the middle of uart_open(), and the core actually had a valid pointer in > state->port.tty, which points to a race between either close or hangup (the only > two places that set state->port.tty to NULL) and open. Close already flushes > the ldisc but hangup does not, which means we could have some characters in the > receive buffer in between the hangup and the open, and we end up in this > situation. Yeah, the race is that the ldisc should not be attempting i/o to the driver at all. This problem is fixed in -next already, but in the tty core rather than in each individual tty driver. Regards, Peter Hurley > Signed-off-by: Josef Bacik <jbacik@xxxxxx> > --- > drivers/tty/serial/serial_core.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c > index b1f54ab..93b7a53 100644 > --- a/drivers/tty/serial/serial_core.c > +++ b/drivers/tty/serial/serial_core.c > @@ -1527,6 +1527,7 @@ static void uart_hangup(struct tty_struct *tty) > wake_up_interruptible(&port->delta_msr_wait); > } > mutex_unlock(&port->mutex); > + tty_ldisc_flush(tty); > } > > static void uart_port_shutdown(struct tty_port *port) > -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
