Re: [PATCH 16/22] xen-blkfront: Make use of the new sg_map helper function

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Apr 18, 2017 at 02:13:59PM +0000, David Laight wrote:
> From: Logan Gunthorpe
> > Sent: 13 April 2017 23:05
> > Straightforward conversion to the new helper, except due to
> > the lack of error path, we have to warn if unmapable memory
> > is ever present in the sgl.

Interesting that you didn't CC any of the maintainers. Could you 
do that in the future please?

> > 
> > Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> > ---
> >  drivers/block/xen-blkfront.c | 33 +++++++++++++++++++++++++++------
> >  1 file changed, 27 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> > index 5067a0a..7dcf41d 100644
> > --- a/drivers/block/xen-blkfront.c
> > +++ b/drivers/block/xen-blkfront.c
> > @@ -807,8 +807,19 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri
> >  		BUG_ON(sg->offset + sg->length > PAGE_SIZE);
> > 
> >  		if (setup.need_copy) {
> > -			setup.bvec_off = sg->offset;
> > -			setup.bvec_data = kmap_atomic(sg_page(sg));
> > +			setup.bvec_off = 0;
> > +			setup.bvec_data = sg_map(sg, SG_KMAP_ATOMIC);
> > +			if (IS_ERR(setup.bvec_data)) {
> > +				/*
> > +				 * This should really never happen unless
> > +				 * the code is changed to use memory that is
> > +				 * not mappable in the sg. Seeing there is a
> > +				 * questionable error path out of here,
> > +				 * we WARN.
> > +				 */
> > +				WARN(1, "Non-mappable memory used in sg!");
> > +				return 1;
> > +			}
> ...
> 
> Perhaps add a flag to mark failure as 'unexpected' and trace (and panic?)
> inside sg_map().
> 
> 	David
> 
> 
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