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    Subject[PATCH 55/58] tty: Push the lock down further into the ldisc code
    Date
    From: Alan Cox <alan@linux.intel.com>

    Signed-off-by: Alan Cox <alan@linux.intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    ---
    drivers/char/tty_io.c | 2 --
    drivers/char/tty_ldisc.c | 12 +++++++++---
    2 files changed, 9 insertions(+), 5 deletions(-)

    diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
    index 1e24130..c408c81 100644
    --- a/drivers/char/tty_io.c
    +++ b/drivers/char/tty_io.c
    @@ -1347,9 +1347,7 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx,
    * If we fail here just call release_tty to clean up. No need
    * to decrement the use counts, as release_tty doesn't care.
    */
    - lock_kernel();
    retval = tty_ldisc_setup(tty, tty->link);
    - unlock_kernel();
    if (retval)
    goto release_mem_out;
    return tty;
    diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
    index d914e77..3f653f7 100644
    --- a/drivers/char/tty_ldisc.c
    +++ b/drivers/char/tty_ldisc.c
    @@ -445,8 +445,14 @@ static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
    static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
    {
    WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
    - if (ld->ops->open)
    - return ld->ops->open(tty);
    + if (ld->ops->open) {
    + int ret;
    + /* BKL here locks verus a hangup event */
    + lock_kernel();
    + ret = ld->ops->open(tty);
    + unlock_kernel();
    + return ret;
    + }
    return 0;
    }

    @@ -566,6 +572,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
    return 0;
    }

    + unlock_kernel();
    /*
    * Problem: What do we do if this blocks ?
    * We could deadlock here
    @@ -573,7 +580,6 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)

    tty_wait_until_sent(tty, 0);

    - unlock_kernel();
    mutex_lock(&tty->ldisc_mutex);

    /*
    --
    1.6.5.5


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