linux-kernel - Re: lockdep splat from fbmem

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Date:	Thu, 23 Oct 2008 15:10:12 +0200
From:	Andrea Righi <righi.andrea@...il.com>
To:	Johannes Weiner <hannes@...urebad.de>
CC:	Krzysztof Helt <krzysztof.h1@...pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: lockdep splat from fbmem

Johannes Weiner wrote:
> 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.
> 
> Just noticed the trace and wanted to let you know.
> 
>         Hannes

Good catch. We could try to push down the mutex and call all the
copy_to/from_user() outside the lock. I can try look at it tonight,
if someone doesn't fix it before.

Thanks for reporting,
-Andrea
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