Subject: Re: tty->low_latency + irq context
From: Hollis Blanchard <hollisb@us.ibm.com>
Reply-To: Hollis Blanchard <hollisb@us.ibm.com>
To: Alan <alan@lxorguk.ukuu.org.uk>
Cc: Jiri Slaby <jirislaby@gmail.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       p.hardwick@option.com
In-Reply-To: <20070102183829.10d861fc@localhost.localdomain>
References: <45906820.10805@gmail.com> <1167758231.5616.22.camel@basalt>
	 <20070102183829.10d861fc@localhost.localdomain>
Content-Type: text/plain
Organization: IBM Linux Technology Center
Date: Tue, 02 Jan 2007 13:36:01 -0600
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On Tue, 2007-01-02 at 18:38 +0000, Alan wrote:
> > with tty->low_latency set, but it doesn't AFAICS. One possibility
> for
> > deadlock is if the tty->buf.lock spinlock is taken on behalf of a
> user
> > process...
> 
> The case to watch out for is
> 
>         flip_buffer_push -> ldisc -> driver write of echo/^S/^Q
> 
> if you call flip_buffer_push while holding your own lock you may get
> in a mess on the echo path. 

Agreed. However, that's not what the comment says:

 *      tty_flip_buffer_push    -       terminal
 *      @tty: tty to push
 *
 *      Queue a push of the terminal flip buffers to the line discipline. This
 *      function must not be called from IRQ context if tty->low_latency is set.

-- 
Hollis Blanchard
IBM Linux Technology Center

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