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    Subject[PATCH 2/5] TTY: serial, move locking in uart_close
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    So now, when we handle CLOSING flag, there is no point to hold
    port->mutex over the start of uart_close.

    Yes, there are still several things to reason about:
    * port->count etc is and always was protected by a spinlock
    * ->stop_rx is protected by a spinlock. Otherwise it would
    race with interrupts.
    * uart_wait_until_sent -- that one is already called without
    port->mutex from set_termios and tty_set_ldisc. Should anything
    be protected there, it would be tx_empty. And by a spinlock.
    8250 does this internally...

    This step is needed to fix system stalls. To not create an AB-BA lock
    dependency (see next patches).

    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    ---
    drivers/tty/serial/serial_core.c | 2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)

    diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
    index cd7a0bb..e1bff1b 100644
    --- a/drivers/tty/serial/serial_core.c
    +++ b/drivers/tty/serial/serial_core.c
    @@ -1258,7 +1258,6 @@ static void uart_close(struct tty_struct *tty, struct file *filp)

    pr_debug("uart_close(%d) called\n", uport->line);

    - mutex_lock(&port->mutex);
    spin_lock_irqsave(&port->lock, flags);

    if (tty_hung_up_p(filp)) {
    @@ -1317,6 +1316,7 @@ static void uart_close(struct tty_struct *tty, struct file *filp)
    uart_wait_until_sent(tty, uport->timeout);
    }

    + mutex_lock(&port->mutex);
    uart_shutdown(tty, state);
    uart_flush_buffer(tty);

    --
    1.7.6



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