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commit211cde4f58upstream. Commit868f3ee6e4("serial: 8250: Add 8250 port clock update method") added a hack to support SoCs where the UART reference clock can change behind the back of the driver but failed to add the proper locking. First, make sure to take a reference to the tty struct to avoid dereferencing a NULL pointer if the clock change races with a hangup. Second, the termios semaphore must be held during the update to prevent a racing termios change. Fixes:868f3ee6e4("serial: 8250: Add 8250 port clock update method") Fixes:c8dff3aa82("serial: 8250: Skip uninitialized TTY port baud rate update") Cc: stable@vger.kernel.org # 5.9 Cc: Serge Semin <Sergey.Semin@baikalelectronics.ru> Tested-by: Serge Semin <fancer.lancer@gmail.com> Reviewed-by: Serge Semin <fancer.lancer@gmail.com> Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Signed-off-by: Johan Hovold <johan@kernel.org> Link: https://lore.kernel.org/r/20211015111422.1027-2-johan@kernel.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>