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    SubjectRe: [Bug #14388] keyboard under X with 2.6.31
    > > I can't help feeling a mutex might be simpler. It would also then fix
    > > tiocsti() which is most definitely broken right now and documented as
    > > racing.
    > Hmm. Those tty's have too many different locks already.
    > But maybe we could just have one generic mutex, and use it for termios and
    > IO locking. It makes perfect sense to serialize the ->receive_buf() code
    > with any termios changes, since termios is what affects _how_ that
    > ->receive_buf() function works.

    You cannot trivially just take the same lock for receive_buf and termios
    locking at the moment. The reason is that receive_buf can cause the tty to
    throttle which causes us to call the throttle methods which take the lock.

    tty_throttle() and tty_unthrottle() can be called from both receive_buf
    and non receive_buf paths so you can't just remove it.

    The better existing lock is probably tty->ldisc_mutex which we take when
    doing ldisc changes (which are an even more dramatic change during
    receive_buf). We don't do ldisc changes from the receive_buf path and it
    opens a path for further simplification of the ldisc logic if we can get
    to the point where the ldisc doesn't get called randomly from the tty
    layer when changing.

    > I do wonder why tiocsti() doesn't just use the tty buffering layer,
    > though? Maybe that harks back to the whole "pty's did things differently"
    > thing? Why does it go directly to ->receive_buf() in the first place?

    Historical question - I don't know - and at the time I commented it there
    was no quick fix and bigger problems to sort first


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