Re: [PATCH tty-next 14/22] tty: Remove tty_wait_until_sent_from_close()

[Peter Hurley]

On 06/17/2014 07:03 AM, David Laight wrote:
> From: Peter Hurley
> ...
> > > I don't understand the second half of the changelog, it doesn't seem
> > > to fit here: there deadlock that we are trying to avoid here happens
> > > when the *same* tty needs the lock to complete the function that
> > > sends the pending data. I don't think we do still do that any more,
> > > but it doesn't seem related to the tty lock being system-wide or not.
> >
> > The tty lock is not used in the i/o path; it's purpose is to
> > mutually exclude state changes in open(), close() and hangup().
> >
> > The commit that added this [1] comments that _other_ ttys may wait
> > for this tty to complete, and comments in the code note that this
> > function should be removed when the system-wide tty mutex was removed
> > (which happened with the commit noted in the changelog).
>
> What happens if another process tries to do a non-blocking open
> while you are sleeping in close waiting for output to drain?
>
> Hopefully this returns before that data has drained.

Good point.

tty_open() should be trylocking both mutexes anyway in O_NONBLOCK.

Regards,
Peter Hurley
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