Re: Possible deadlock in videobuf_dma_init_user

From: Arjan van de Ven
Date: Sun Aug 20 2006 - 15:47:39 EST

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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