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    Subject[PATCH AUTOSEL 5.15 13/51] drivers: tty: serial: Fix deadlock in sa1100_set_termios()
    Date
    From: Duoming Zhou <duoming@zju.edu.cn>

    [ Upstream commit 62b2caef400c1738b6d22f636c628d9f85cd4c4c ]

    There is a deadlock in sa1100_set_termios(), which is shown
    below:

    (Thread 1) | (Thread 2)
    | sa1100_enable_ms()
    sa1100_set_termios() | mod_timer()
    spin_lock_irqsave() //(1) | (wait a time)
    ... | sa1100_timeout()
    del_timer_sync() | spin_lock_irqsave() //(2)
    (wait timer to stop) | ...

    We hold sport->port.lock in position (1) of thread 1 and
    use del_timer_sync() to wait timer to stop, but timer handler
    also need sport->port.lock in position (2) of thread 2. As a result,
    sa1100_set_termios() will block forever.

    This patch moves del_timer_sync() before spin_lock_irqsave()
    in order to prevent the deadlock.

    Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
    Link: https://lore.kernel.org/r/20220417111626.7802-1-duoming@zju.edu.cn
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/tty/serial/sa1100.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/drivers/tty/serial/sa1100.c b/drivers/tty/serial/sa1100.c
    index 697b6a002a16..4ddcc985621a 100644
    --- a/drivers/tty/serial/sa1100.c
    +++ b/drivers/tty/serial/sa1100.c
    @@ -446,6 +446,8 @@ sa1100_set_termios(struct uart_port *port, struct ktermios *termios,
    baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16);
    quot = uart_get_divisor(port, baud);

    + del_timer_sync(&sport->timer);
    +
    spin_lock_irqsave(&sport->port.lock, flags);

    sport->port.read_status_mask &= UTSR0_TO_SM(UTSR0_TFS);
    @@ -476,8 +478,6 @@ sa1100_set_termios(struct uart_port *port, struct ktermios *termios,
    UTSR1_TO_SM(UTSR1_ROR);
    }

    - del_timer_sync(&sport->timer);
    -
    /*
    * Update the per-port timeout.
    */
    --
    2.35.1
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