linux-kernel - Re: [bug] Fixing mutex_lock() under held spinlock

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Message-Id: <201007291534.57188.arnd@arndb.de>
Date:	Thu, 29 Jul 2010 15:34:56 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Vasiliy Kulikov <segooon@...il.com>
Cc:	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>,
	David Woodhouse <David.Woodhouse@...el.com>,
	Nicolas Pitre <nico@...xnic.net>,
	"Hans-Christian Egtvedt" <hans-christian.egtvedt@...el.com>,
	Jiri Slaby <jslaby@...e.cz>,
	Stefani Seibold <stefani@...bold.net>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [bug] Fixing mutex_lock() under held spinlock

On Thursday 29 July 2010, Vasiliy Kulikov wrote:
> I've found that cfi_cmdset and lpddr_cmds call mutex_lock() under held
> spinlock(). Maybe it was designed as a special locking scheme, so I
> don't try to fix it as I might create new complex locking problem.

No, it certainly looks like a bug and it seems to have been introduced by
http://linux.derkeiler.com/Mailing-Lists/Kernel/2010-03/msg02798.html

Back in March, Stefani wrote:
| I have analyzed this drivers and IMHO i don't think there will be used
| from irq or atomic contexts. There is no request interrupt and there are
| a lot msleep and add_wait_queues/schedule calls during holding the
| mutex, which are not very useful in a irq or atomic context. But i don't
| know the whole mtd stack. 

It seems you have missed at least two places. It should be possible to
fix this by turning shared->lock into a mutex as well.

	Arnd
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