linux-kernel - Re: [PATCH] Use tty

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Message-ID: <Pine.LNX.4.64.0707172104050.9131@pentafluge.infradead.org>
Date:	Tue, 17 Jul 2007 21:15:26 +0100 (BST)
From:	James Simmons <jsimmons@...radead.org>
To:	Paul Fulghum <paulkf@...rogate.com>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux console project <linuxconsole-dev@...ts.sourceforge.net>
Subject: Re: [PATCH] Use tty_schedule in VT code.


> James Simmons wrote:
> > Because sometimes you do want the delay. In other parts of the tty code we
> > do delay. What should be done is 
> 
> Correct, so we must stick with the delayed work structure
> which requires calling the delayed work function.
> 
> >         if (tty->low_latency)
> >                 flush_to_ldisc(&tty->buf.work.work);
> >         else
> >                 schedule_delayed_work(&tty->buf.work, 1);
> > 
> > Is this acceptable to you?
> 
> That does not make sense to me.
> 
> If you are calling from interrupt context, you do not want
> to call flush_to_ldisc() directly regardless of low_latency.
> This used to be the way it was done and it ended up causing
> deadlocks in just that situation.

The low_latency is used by the drivers in the case where its 
not in a interrupt context. Well we are trusting the drivers.
Now if it is true what you said then tty_flip_buffer_push has
a bug. Looking at several drivers including serial devices
they set the low_latency flag.

> And the initial schedule has no reason to add the extra delay.

So do you support a non delay work queue as well?


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