linux-kernel - Re: [PATCH tty-next 14/22] tty: Remove tty_wait_until_sent_from

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Message-ID: <4575870.N9RCpZ4UMg@wuerfel>
Date:	Tue, 17 Jun 2014 10:00:59 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linuxppc-dev@...ts.ozlabs.org
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Karsten Keil <isdn@...ux-pingi.de>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH tty-next 14/22] tty: Remove tty_wait_until_sent_from_close()

On Monday 16 June 2014 09:17:11 Peter Hurley wrote:
> tty_wait_until_sent_from_close() drops the tty lock while waiting
> for the tty driver to finish sending previously accepted data (ie.,
> data remaining in its write buffer and transmit fifo).
> 
> However, dropping the tty lock is a hold-over from when the tty
> lock was system-wide; ie., one lock for all ttys.
> 
> Since commit 89c8d91e31f267703e365593f6bfebb9f6d2ad01,
> 'tty: localise the lock', dropping the tty lock has not been necessary.
> 
> CC: Karsten Keil <isdn@...ux-pingi.de>
> CC: linuxppc-dev@...ts.ozlabs.org
> Signed-off-by: Peter Hurley <peter@...leysoftware.com>

I don't understand the second half of the changelog, it doesn't seem
to fit here: there deadlock that we are trying to avoid here happens
when the *same* tty needs the lock to complete the function that
sends the pending data. I don't think we do still do that any more,
but it doesn't seem related to the tty lock being system-wide or not.

	Arnd
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