Messages in this thread |  | | | Date | Wed, 14 Oct 2009 00:11:31 +0100 | | From | Alan Cox <> | | Subject | Re: [Bug #14388] keyboard under X with 2.6.31 |
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> > 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
Alan
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