V4L/DVB (6268): V4L: Fix a lock inversion in generic videobuf code
commit9900132f3437e9373aa030cdb5bd2d5db15566e3
authorMaxim Levitsky <maximlevitsky@gmail.com>
Thu, 27 Sep 2007 23:34:09 +0000 (27 20:34 -0300)
committerMauro Carvalho Chehab <mchehab@infradead.org>
Wed, 10 Oct 2007 03:02:58 +0000 (10 00:02 -0300)
treeb4b450daf16d1f502869dd472ae2bad85892daca
parent851c0c96b2212f48fe51afc1589541b5eae3a544
V4L/DVB (6268): V4L: Fix a lock inversion in generic videobuf code

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