Re: [RFC][PATCH v3 6/6] fix wrong get_user_pages usage in iovlock.c

Nick Piggin
2009-04-14T06:56:11Z

On Tuesday 14 April 2009 16:23:13 KOSAKI Motohiro wrote:
> I don't have NET-DMA usable device. I hope to get expert review.
>
> =========================
> Subject: [Untested][RFC][PATCH] fix wrong get_user_pages usage in iovlock.c
>
> down_read(mmap_sem)
> get_user_pages()
> up_read(mmap_sem)
>
> is fork unsafe.
> fix it.
>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Cc: Maciej Sosnowski <maciej.sosnowski@intel.com>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Chris Leech <christopher.leech@intel.com>
> Cc: netdev@vger.kernel.org
> ---
> drivers/dma/iovlock.c | 18 ++++++------------
> 1 file changed, 6 insertions(+), 12 deletions(-)
>
> Index: b/drivers/dma/iovlock.c
> ===================================================================
> --- a/drivers/dma/iovlock.c 2009-02-21 16:53:23.000000000 +0900
> +++ b/drivers/dma/iovlock.c 2009-04-13 04:46:02.000000000 +0900
> @@ -94,18 +94,10 @@ struct dma_pinned_list *dma_pin_iovec_pa
> pages += page_list->nr_pages;
>
> /* pin pages down */
> - down_read(&current->mm->mmap_sem);
> - ret = get_user_pages(
> - current,
> - current->mm,
> - (unsigned long) iov[i].iov_base,
> - page_list->nr_pages,
> - 1, /* write */
> - 0, /* force */
> - page_list->pages,
> - NULL);
> - up_read(&current->mm->mmap_sem);
> -
> + down_read(&current->mm->mm_pinned_sem);
> + ret = get_user_pages_fast((unsigned long) iov[i].iov_base,
> + page_list->nr_pages, 1,
> + page_list->pages);

I would perhaps not fold gup_fast conversions into the same patch as
the fix.