linux-kernel - Re: BUG: scheduling while atomic

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Message-ID: <20090706110014.5cbcc2d7@lxorguk.ukuu.org.uk>
Date:	Mon, 6 Jul 2009 11:00:14 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Michael Guntsche <mike@...loops.com>, linux-kernel@...r.kernel.org
Subject: Re: BUG: scheduling while atomic

> So what see here is that on xmit from the network,
> PPP will call pty_write from BH context which eventually leads
> to tty_throttle and the sleep.

That would I fit the symptoms and also explain why some broken versions
of the USB code on embedded devices also exploded with PPP over USB links.

Not however at all easy to fix as it only ever worked in the past on the
"close both eyes, pray and jump" principle of locking.

Added to the todo list for later this week. The pty layer has all sorts
of magic hackery to allow it to call back and forth without going via
internal tty buffering like normal hardware. That may have to die as it
causes other horrible problems too.

Alan
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