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Date:   Wed, 16 Dec 2020 16:48:38 -0800
From:   Jakub Kicinski <kuba@kernel.org>
To:     Gao Yan <gao.yanB@h3c.com>
Cc:     <paulus@samba.org>, <davem@davemloft.net>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] net: remove disc_data_lock in ppp line discipline
Message-ID: <20201216164838.55f939a2@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
In-Reply-To: <20201215150054.570-1-gao.yanB@h3c.com>
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On Tue, 15 Dec 2020 23:00:54 +0800 Gao Yan wrote:
> tty layer provide tty->ldisc_sem lock to protect tty->disc_data;
> For examlpe, when cpu A is running ppp_synctty_ioctl that
> hold the tty->ldisc_sem, so if cpu B calls ppp_synctty_close,
> it will wait until cpu A release tty->ldisc_sem. So I think it is
> unnecessary to have the disc_data_lock;
> 
> cpu A                           cpu B
> tty_ioctl                       tty_reopen
>  ->hold tty->ldisc_sem            ->hold tty->ldisc_sem(write), failed
>  ->ld->ops->ioctl                 ->wait...
>  ->release tty->ldisc_sem         ->wait...OK,hold tty->ldisc_sem
>                                     ->tty_ldisc_reinit
>                                       ->tty_ldisc_close
>                                         ->ld->ops->close  
> 
> Signed-off-by: Gao Yan <gao.yanB@h3c.com>

# Form letter - net-next is closed

We have already sent the networking pull request for 5.11 and therefore
net-next is closed for new drivers, features, code refactoring and
optimizations. We are currently accepting bug fixes only.

Please repost when net-next reopens after 5.11-rc1 is cut.

Look out for the announcement on the mailing list or check:
http://vger.kernel.org/~davem/net-next.html

RFC patches sent for review only are obviously welcome at any time.