Re: [PATCH] tty: Add driver unthrottle in ioctl(...,TCFLSH,..).

[Ilya Zykov]

On 22.11.2012 4:47, andrew mcgregor wrote:
> > > > On 11/22/2012 at 10:39 AM, in message <50AD4A01.7060500@xxxxxxx>, Ilya Zykov
> <ilya@xxxxxxx> 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).


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