linux-kernel - Re: Possible deadlock in videobuf_dma_init

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Date:	Sun, 20 Aug 2006 21:50:15 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	Petr Vandrovec <petr@...drovec.name>
Cc:	video4linux-list@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: Possible deadlock in videobuf_dma_init_user

On Sun, 2006-08-20 at 21:19 +0200, Petr Vandrovec wrote:
> Hello,
>   my kernel is a bit unhappy with lock ordering between mm->mmap_sem 
> and videobuf_queue->lock.
> 					Thanks,
> 						Petr Vandrovec


looks like a real deadlock to me...

bttv_prepare_buffer takes mutex then
videobuf_dma_init_user takes mmap_sem



do_mmap_pgoff takes mmap_sem then calls
bttv_mmap which calls
videobuf_mmap_mapper takes the mutex


so a classic AB-BA deadlock....


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