Hi Jan, Thank you for the patch.
On Wednesday 02 October 2013 16:27:46 Jan Kara wrote: > CC: Laurent Pinchart <[email protected]> > CC: [email protected] > Signed-off-by: Jan Kara <[email protected]> Acked-by: Laurent Pinchart <[email protected]> Could you briefly explain where you're headed with this ? The V4L2 subsystem has suffered for quite a long time from potentiel AB-BA deadlocks, due the drivers taking the mmap_sem semaphore while holding the V4L2 buffers queue lock in the code path below, and taking them in reverse order in the mmap() path (as the mm core takes the mmap_sem semaphore before calling the mmap() operation). We've solved that by releasing the V4L2 buffers queue lock before taking the mmap_sem lock below and taking it back after releasing the mmap_sem lock. Having an explicit indication that the mmap_sem lock was taken helped keeping the problem in mind. I'm not against hiding it in get_user_pages_fast(), but I'd like to know what the next step is. Maybe it would also be worth it adding a /* get_user_pages_fast() takes the mmap_sem */ comment before the call ? > --- > drivers/media/platform/omap3isp/ispqueue.c | 10 +++------- > 1 file changed, 3 insertions(+), 7 deletions(-) > > diff --git a/drivers/media/platform/omap3isp/ispqueue.c > b/drivers/media/platform/omap3isp/ispqueue.c index > e15f01342058..bed380395e6c 100644 > --- a/drivers/media/platform/omap3isp/ispqueue.c > +++ b/drivers/media/platform/omap3isp/ispqueue.c > @@ -331,13 +331,9 @@ static int isp_video_buffer_prepare_user(struct > isp_video_buffer *buf) if (buf->pages == NULL) > return -ENOMEM; > > - down_read(¤t->mm->mmap_sem); > - ret = get_user_pages(current, current->mm, data & PAGE_MASK, > - buf->npages, > - buf->vbuf.type == V4L2_BUF_TYPE_VIDEO_CAPTURE, 0, > - buf->pages, NULL); > - up_read(¤t->mm->mmap_sem); > - > + ret = get_user_pages_fast(data & PAGE_MASK, buf->npages, > + buf->vbuf.type == V4L2_BUF_TYPE_VIDEO_CAPTURE, > + buf->pages); > if (ret != buf->npages) { > buf->npages = ret < 0 ? 0 : ret; > isp_video_buffer_cleanup(buf); -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
