From: Ilya Zykov <ilya@ilyx.ru>
To: Alan Cox <alan@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>, linux-kernel@vger.kernel.org
Subject: Re: PROBLEM: Race condition in tty buffer's function flush_to_ldisc().
Date: Mon, 07 Nov 2011 17:44:38 +0400 [thread overview]
Message-ID: <4EB7E0C6.7050909@ilyx.ru> (raw)
In-Reply-To: <20111107130643.07e84fca@bob.linux.org.uk>
Alan Cox wrote:
>
>> 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.
>
> It is single threaded with respect to itself (you can't have two
> flush_to_ldisc on the same tty at once) but you can have a parallel
> call to tty_buffer_flush. The tty_buffer_flush path needs to pick the
> right approach reliably.
>
Of course I know about tty_buffer_flush(), it only read TTY_FLUSHING,
it can't change TTY_FLUSHING, if flush_to_ldisc() single threaded,
we can change TTY_FLUSHING only in one place in one time(in flush_to_ldisc()),
therefor we can use only "set_bit(TTY_FLUSHING, &tty->flags)" without test.
next prev parent reply other threads:[~2011-11-07 13:44 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-07 11:14 PROBLEM: Race condition in tty buffer's function flush_to_ldisc() Ilya Zykov
2011-11-07 11:58 ` Alan Cox
2011-11-07 12:20 ` Ilya Zykov
2011-11-07 13:06 ` Alan Cox
2011-11-07 13:44 ` Ilya Zykov [this message]
2011-11-07 14:50 ` Alan Cox
2011-11-07 14:52 ` Ilya Zykov
2011-11-07 18:26 ` Ilya Zykov
2011-11-07 18:39 ` Alan Cox
2011-11-07 18:41 ` Alan Cox
2011-11-07 12:35 ` Ilya Zykov
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