From: "andrew mcgregor" <andrew.mcgregor@alliedtelesis.co.nz>
To: "Ilya Zykov" <ilya@ilyx.ru>
Cc: "Alan Cox" <alan@linux.intel.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] tty: Add driver unthrottle in ioctl(...,TCFLSH,..).
Date: Thu, 22 Nov 2012 18:25:09 +1300 [thread overview]
Message-ID: <50AE6E050200003600026BD7@gwia.alliedtelesyn.co.nz> (raw)
In-Reply-To: <50ADAA26.7080103@ilyx.ru>
>>> On 11/22/2012 at 05:29 PM, in message <50ADAA26.7080103@ilyx.ru>, Ilya Zykov
<ilya@ilyx.ru> wrote:
> On 22.11.2012 4:47, andrew mcgregor wrote:
> >
> >
> >>>> On 11/22/2012 at 10:39 AM, in message <50AD4A01.7060500@ilyx.ru>, Ilya Zykov
> > <ilya@ilyx.ru> wrote:
> >> On 22.11.2012 1:30, Alan Cox wrote:
> >>>> Function reset_buffer_flags() also invoked during the
> >>>> ioctl(...,TCFLSH,..). At the time of request we can have full buffers
> >>>> and throttled driver too. If we don't unthrottle driver, we can get
> >>>> forever throttled driver, because after request, we will have
> >>>> empty buffers and throttled driver and there is no place to unthrottle
> >> driver.
> >>>> It simple reproduce with "pty" pair then one side sleep on tty->write_wait,
> >>>> and other side do ioctl(...,TCFLSH,..). Then there is no place to do
> >> writers wake up.
> >>>
> >>>
> >>> So instead of revertng it why not just fix it ? Just add an argument to
> >>> the reset_buffer_flags function to indicate if unthrottling is permitted.
> >>>
> >>> Alan
> >>>
> >> Because in my opinion, unthrottling permitted always, except release
> >> last filp (tty->count == 0)
> >
> > Maybe so, but the patch was there in the first place to resolve an actual
> observed bug, where a driver would lock up. So the behaviour needs
> preserved.
> >
> > Andrew
> >
>
> Maybe it was wrong driver, unfortunately, I didn't find full information
> about this bug. As an example, if driver indirectly call
> reset_buffer_flags() in driver's close() function it will be before
> decrement last (tty->count).
Well, the driver in question was just 8250.c, so you should be able to see that the original condition can exist.
Here's the commit message again:
tty: fix "IRQ45: nobody cared"
Unthrottling the TTY during close ends up enabling interrupts
on a device not on the active list, which will never have the
interrupts cleared. Doctor, it hurts when I do this.
>>> On 6/2/2011 at 01:56 AM, in message <20110601145608.3e586e16@bob.linux.org.uk>, Alan Cox <alan@linux.intel.com> wrote:
> On Wed, 01 Jun 2011 10:34:07 +1200
> "andrew mcgregor" <andrew.mcgregor@alliedtelesis.co.nz> wrote:
> > The LKML message
> > http://kerneltrap.org/mailarchive/linux-kernel/2010/2/25/4541847from
> > February doesn't seem to have been resolved since. We struck the
> > issue, and the patch below (against 2.6.32) fixes it. Should I
> > supply a patch against 3.0.0rc?
>
> I think that would be sensible. I don't actually see how you hit it as
> the IRQ ought to be masked by then but it's certainly wrong for n_tty
> to be calling into check_unthrottle at that point.
>
> So yes please send a patch with a suitable Signed-off-by: line to
> linux-serial and cc GregKH <greg@kroah.com> as well.
>
> Alan
Signed-off-by: Andrew McGregor <andrew.mcgregor@alliedtelesis.co.nz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
What part of this no longer applies? I'm happy enough if you can prove that this can't happen any more, but otherwise the fix should remain.
Andrew
next prev parent reply other threads:[~2012-11-22 21:25 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-21 21:12 [PATCH] tty: Add driver unthrottle in ioctl(...,TCFLSH,..) Ilya Zykov
2012-11-21 21:30 ` Alan Cox
2012-11-21 21:39 ` Ilya Zykov
2012-11-22 0:47 ` andrew mcgregor
2012-11-22 4:29 ` Ilya Zykov
2012-11-22 5:25 ` andrew mcgregor [this message]
2012-11-22 6:35 ` Ilya Zykov
2012-11-22 6:03 ` Ilya Zykov
2012-11-22 6:16 ` Ilya Zykov
2012-11-21 21:55 ` Ilya Zykov
2012-11-27 6:14 [PATCH v4] " Ilya Zykov
2012-11-27 17:24 ` Greg Kroah-Hartman
2012-11-27 18:46 ` Ilya Zykov
2012-11-27 19:32 ` Alan Cox
2013-01-16 9:07 ` [PATCH] " Ilya Zykov
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