V4L/DVB (6268): V4L: Fix a lock inversion in generic videobuf code

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videobuf_qbuf takes q->lock, and then calls
q->ops->buf_prepare which by design in all drivers calls
videobuf_iolock which calls videobuf_dma_init_user and this
takes current->mm->mmap_sem

on the other hand if user calls mumap from other thread, sys_munmap
takes current->mm->mmap_sem and videobuf_vm_close takes q->lock

Since this can occur only for V4L2_MEMORY_MMAP buffers, take
current->mm->mmap_sem in qbuf, before q->lock, and don't take
current->mm->mmap_sem videobuf_dma_init_user for those buffers

Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
http://thread.gmane.org/gmane.comp.video.video4linux/34978/focus=34981
Reviewed-by: Ricardo Cerqueira <v4l@cerqueira.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

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Maxim Levitsky 2007-09-27 20:34:09 -03:00 • committed by Mauro Carvalho Chehab

parent 851c0c96b2

commit 9900132f34

2 changed files with 34 additions and 5 deletions

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7

drivers/media/video/videobuf-core.c

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32

drivers/media/video/videobuf-dma-sg.c

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