linux-kernel - Re: PROBLEM: Race condition in tty buffer's function flush_to

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Message-ID: <4EB7D0A4.405@ilyx.ru>
Date:	Mon, 07 Nov 2011 16:35:48 +0400
From:	Ilya Zykov <ilya@...x.ru>
To:	Alan Cox <alan@...ux.intel.com>
CC:	Greg Kroah-Hartman <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	Ilya Zykov <ilya@...x.ru>
Subject: Re: PROBLEM: Race condition in tty buffer's function flush_to_ldisc().

Alan Cox wrote:

> On Mon, 07 Nov 2011 15:14:34 +0400
> Ilya Zykov <ilya@...x.ru> wrote:
> 
>> Function flush_to_ldisc() call disc->ops->receive_buf(),
>> without tty->buf.lock and with TTY_FLUSHING bit set.
> 
> flush_to_ldisc is single threaded for a given tty. If you fail to
> ensure that is the case everything breaks.


Why we need: "if (!test_and_set_bit(TTY_FLUSHING, &tty->flags)) {"
if flush_to_ldisc is single threaded?
we can: set_bit(TTY_FLUSHING, &tty->flags)
without if() at all.

> 
> What cases does this occur ?
> 
> Also for the other patches do you have benchmarks yet ?
> 
> Alan
> 


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