netdev - Re: ppp: Fix race condition with queue start/stop

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Message-Id: <20120413.130707.1734763456520627875.davem@davemloft.net>
Date:	Fri, 13 Apr 2012 13:07:07 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	dwmw2@...radead.org
Cc:	paulus@...ba.org, netdev@...r.kernel.org
Subject: Re: ppp: Fix race condition with queue start/stop

From: David Woodhouse <dwmw2@...radead.org>
Date: Sun, 08 Apr 2012 21:01:44 +0100

> Commit e675f0cc9a872fd152edc0c77acfed19bf28b81e ("ppp: Don't stop and
> restart queue on every TX packet") introduced a race condition which
> could leave the net queue stopped even when the channel is no longer
> busy. By calling netif_stop_queue() from ppp_start_xmit(), based on the
> return value from ppp_xmit_process() but *after* all the locks have been
> dropped, we could potentially do so *after* the channel has actually
> finished transmitting and attempted to re-wake the queue.
> 
> Fix this by moving the netif_stop_queue() into ppp_xmit_process() under
> the xmit lock. I hadn't done this previously, because it gets called
> from other places than ppp_start_xmit(). But I now think it's the better
> option. The net queue *should* be stopped if the channel becomes
> congested due to writes from pppd, anyway.
> 
> Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>

Applied, thanks David.
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