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

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Message-ID: <20121121213037.154306da@pyramind.ukuu.org.uk>
Date:	Wed, 21 Nov 2012 21:30:37 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Ilya Zykov <ilya@...x.ru>
Cc:	Andrew McGregor <andrew.mcgregor@...iedtelesis.co.nz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Cox <alan@...ux.intel.com>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH] tty: Add driver unthrottle in ioctl(...,TCFLSH,..).

> 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
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