linux-kernel - Re: [PATCH v3 16/23] tty: Make core responsible for synchronizing its work

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Message-ID: <1360098260.3298.27.camel@thor.lan>
Date:	Tue, 05 Feb 2013 16:04:20 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Alan Cox <alan@...ux.intel.com>, Jiri Slaby <jslaby@...e.cz>,
	Sasha Levin <levinsasha928@...il.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ilya Zykov <ilya@...x.ru>, Dave Jones <davej@...hat.com>
Subject: Re: [PATCH v3 16/23] tty: Make core responsible for synchronizing
 its work

On Tue, 2013-02-05 at 15:20 -0500, Peter Hurley wrote:
> The tty core relies on the ldisc layer for synchronizing destruction
> of the tty. Instead, the final tty release must wait for any pending tty
> work to complete prior to tty destruction.
> 
> Signed-off-by: Peter Hurley <peter@...leysoftware.com>
> ---
>  drivers/tty/tty_io.c    | 17 +++++++++++++++++
>  drivers/tty/tty_ldisc.c | 24 ++++--------------------
>  2 files changed, 21 insertions(+), 20 deletions(-)

...

> diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
> index e0fdfec..c2837b2 100644
> --- a/drivers/tty/tty_ldisc.c
> +++ b/drivers/tty/tty_ldisc.c
> @@ -499,18 +499,6 @@ static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
>  }
>  
>  /**
> - *	tty_ldisc_flush_works	-	flush all works of a tty
> - *	@tty: tty device to flush works for
> - *
> - *	Sync flush all works belonging to @tty.
> - */
> -static void tty_ldisc_flush_works(struct tty_struct *tty)
> -{
> -	flush_work(&tty->SAK_work);
> -	flush_work(&tty->hangup_work);
> -}
> -
> -/**
>   *	tty_ldisc_wait_idle	-	wait for the ldisc to become idle
>   *	@tty: tty to wait for
>   *	@timeout: for how long to wait at most
> @@ -726,13 +714,13 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
>  	retval = tty_ldisc_halt(tty, o_tty, &work, &o_work, 5 * HZ);
>  
>  	/*
> -	 * Wait for ->hangup_work to terminate.
> +	 * Wait for hangup to complete, if pending.
>  	 * We must drop the mutex here in case a hangup is also in process.
>  	 */
>  
>  	mutex_unlock(&tty->ldisc_mutex);
>  
> -	tty_ldisc_flush_works(tty);
> +	flush_work(&tty->hangup_work);

Careful review will note that I dropped waiting for SAK. That's because
it makes no sense to wait for SAK_work here -- ie., while setting a new
ldisc. The SAK work can just as easily run at the completion of
tty_set_ldisc() at tty_unlock().

I believe this is an artifact of the formerly shared code.

But maybe I should note that in the commit message?


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