linux-kernel - Re: 'scheduling while atomic' during ppp connection on 2.6.37.1 and 2.6.38

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Message-ID: <20110331223914.458a36b7@lxorguk.ukuu.org.uk>
Date:	Thu, 31 Mar 2011 22:39:14 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	Jack Stone <jwjstone@...tmail.fm>, Mac <kmac@...zta.fm>,
	linux-kernel@...r.kernel.org, linux-ppp@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Jiri Slaby <jirislaby@...il.com>
Subject: Re: 'scheduling while atomic' during ppp connection on 2.6.37.1 and
 2.6.38

> What is the proper way to avoid a race with HUP in tty->ops->write,
> chars_in_buffer, ntty_write_room and possibly others?

You shouldn't need to do anything in those cases as tty and
tty->driver_data won't be going anywhere. port->tty may go NULL and the
IRQ handlers etc need to get the refs properly and keep refs when needed
so the tty isn't freed under them, but that *should* be all that is
needed if the logic is right.

> I looked into the drivers, moxa tests tty->driver_data (why? [1]), mxser
> does nothing as well as rocket and many others. What is the reference
> driver I should look into?

I think its a delusion from early drivers that never got sorted

> 
> [1] Perhaps leftover from when moxa_shutdown used to NULL it.
> 
> I don't see why the driver should care at all. It has a tty,
> tty->driver_data and thus all the HW info. So it should ignore the race,
> i.e. test nothing, right?

Yes

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