linux-kernel - RE: [PATCH 16/22] xen-blkfront: Make use of the new sg

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6DCFFD3CD7@AcuExch.aculab.com>
Date:   Tue, 18 Apr 2017 14:13:59 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Logan Gunthorpe' <logang@...tatee.com>,
        Christoph Hellwig <hch@....de>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Sagi Grimberg <sagi@...mberg.me>, Jens Axboe <axboe@...nel.dk>,
        Tejun Heo <tj@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Ming Lin <ming.l@....samsung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
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        "fcoe-devel@...n-fcoe.org" <fcoe-devel@...n-fcoe.org>,
        "open-iscsi@...glegroups.com" <open-iscsi@...glegroups.com>,
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        "sparmaintainer@...sys.com" <sparmaintainer@...sys.com>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "target-devel@...r.kernel.org" <target-devel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "rds-devel@....oracle.com" <rds-devel@....oracle.com>
CC:     Steve Wise <swise@...ngridcomputing.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: RE: [PATCH 16/22] xen-blkfront: Make use of the new sg_map helper
 function

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.
> 
> Signed-off-by: Logan Gunthorpe <logang@...tatee.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