linux-kernel - lockdep splat from ioctl and mmap fops sharing lock

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Date:	Thu, 23 Oct 2008 15:58:10 +0200
From:	Johannes Weiner <hannes@...urebad.de>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Andrea Righi <righi.andrea@...il.com>,
	Dave Jones <davej@...hat.com>,
	Dave Airlie <airlied@...hat.com>,
	Stefan Richter <stefanr@...6.in-berlin.de>
Subject: lockdep splat from ioctl and mmap fops sharing lock

Johannes Weiner <hannes@...urebad.de> writes:

> Hi,
>
> fb_mmap() is called under mmap_sem and acquires fb_info->lock.
>
> Since 3e680aae4e53ab "fb: convert lock/unlock_kernel() into local fb
> mutex", fb_ioctl() takes fb_info->lock and does copy_to/from_user()
> under it, which in turn might acquire mmap_sem.

More affected drivers:

agp_ioctl() doing usercopy under agp_fe.agp_mutex
agp_mmap() taking agp_fe.agp_mutex under mmap_sem

dv1394_write() doing usercopy under video->mtx
dv1394_mmap() taking video->mtx under mmap_sem

raw1394_ioctl() doing usercopy under fi->state_mutex
raw1394_mmap() taking fi->state_mutex under mmap_sem

	Hannes
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