[PATCH v1] tty: serial: 8250: Fix possible race in serial8250_em485_destroy()

[Matwey V. Kornilov]

Fix possbile race in serial8250_em485_destroy() when timer handlers can
dereference p->em485 which is alread destroyed but not yet NULLed.

Signed-off-by: Matwey V. Kornilov <mat...@sai.msu.ru>
---
I've found that Greg applied initial patchset, so this erratum goes as separate 
patch.

 drivers/tty/serial/8250/8250_port.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c 
b/drivers/tty/serial/8250/8250_port.c
index c908b77..d962de2 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -617,14 +617,16 @@ EXPORT_SYMBOL_GPL(serial8250_em485_init);
  */
 void serial8250_em485_destroy(struct uart_8250_port *p)
 {
-       if (p->em485 == NULL)
+       struct uart_8250_em485 *em485 = p->em485;
+
+       if (!em485)
                return;
 
-       del_timer(&p->em485->start_tx_timer);
-       del_timer(&p->em485->stop_tx_timer);
+       del_timer(&em485->start_tx_timer);
+       del_timer(&em485->stop_tx_timer);
 
-       kfree(p->em485);
        p->em485 = NULL;
+       kfree(em485);
 }
 EXPORT_SYMBOL_GPL(serial8250_em485_destroy);
 
-- 
2.7.0