There are deadlocks caused by del_timer_sync(&priv->hang_timer) and
del_timer_sync(&priv->rr_timer) in grcan_close(), one of the deadlocks
are shown below:

   (Thread 1)              |      (Thread 2)
                           | grcan_reset_timer()
grcan_close()              |  mod_timer()
 spin_lock_irqsave() //(1) |  (wait a time)
 ...                       | grcan_initiate_running_reset()
 del_timer_sync()          |  spin_lock_irqsave() //(2)
 (wait timer to stop)      |  ...

We hold priv->lock in position (1) of thread 1 and use
del_timer_sync() to wait timer to stop, but timer handler also need
priv->lock in position (2) of thread 2. As a result, grcan_close()
will block forever.

This patch extracts del_timer_sync() from the protection of
spin_lock_irqsave(), which could let timer handler to obtain the
needed lock.

Link: https://lore.kernel.org/all/20220425042400.66517-1-duoming@zju.edu.cn
Fixes: 6cec9b07 ("can: grcan: Add device driver for GRCAN and GRHCAN cores")
Cc: stable@vger.kernel.org
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>