From: Ilya Zykov <ilya@ilyx.ru>
To: andrew mcgregor <andrew.mcgregor@alliedtelesis.co.nz>
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 08:29:26 +0400 [thread overview]
Message-ID: <50ADAA26.7080103@ilyx.ru> (raw)
In-Reply-To: <50AE2CE30200003600026B9A@gwia.alliedtelesyn.co.nz>
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).
next prev parent reply other threads:[~2012-11-22 19:15 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 [this message]
2012-11-22 5:25 ` andrew mcgregor
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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