Re: sg: Free data buffers after calling blk_rq_unmap_user

[Christof Schmitt <christof.schmitt@de.ibm.com>]

On Thu, Sep 17, 2009 at 03:00:44PM +0900, FUJITA Tomonori wrote:
> Sorry for the delay,
> 
> On Tue, 15 Sep 2009 18:53:57 +0200
> Christof Schmitt <christof.schmitt@de.ibm.com> wrote:
> 
> > This patch fixes a problem with the sg driver that is only visible
> > with the CONFIG_DEBUG_PAGEALLOC kernel config option. The patch works
> > for me, but i would appreciate the review of somebody with more
> > knowledge about the interactions between the sg driver and the block
> > layer.
> > 
> > Christof
> > ---
> > sg: Free data buffers after calling blk_rq_unmap_user
> > 
> > From: Christof Schmitt <christof.schmitt@de.ibm.com>
> > 
> > Running sg_luns on s390x with CONFIG_DEBUG_PAGEALLOC enabled fails
> > with EFAULT from the SG_IO ioctl. The EFAULT is the result from
> > copy_to_user failing in this call chain:
> > 
> > sg_ioctl
> > sg_new_read
> > sg_finish_rem_req
> > blk_rq_unmap_user
> > __blk_rq_unmap_user
> > bio_uncopy_user
> > __bio_copy_iov
> > copy_to_user
> > 
> > The sg driver calls sg_remove_scat to free the memory pages before
> > calling blk_rq_unmap_user that tries to copy the data back to
> > userspace. Change the order to first call blk_rq_unmap_user before
> > freeing the pages in sg_remove_scat.
> > 
> > Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
> > ---
> >  drivers/scsi/sg.c |   10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> Oops, thanks a lot!
> 
> Acked-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
> 
> It would be better to add "Cc: stable@kernel.org" tag since this fix
> needs to be sent to stable trees.

Thanks for the review. I will resend the patch with the added acked-by
and cc.

--
Christof