xen/blkfront: read response from backend only once

commit 71b66243f9898d0e54296b4e7035fb33cdcb0707 upstream.

In order to avoid problems in case the backend is modifying a response
on the ring page while the frontend has already seen it, just read the
response into a local buffer in one go and then operate on that buffer
only.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Link: https://lore.kernel.org/r/20210730103854.12681-2-jgross@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index e1f71debdbbaa6b417e72a3d1c27a524876fb76f..abcb6b2e0e319a6f07d540642c2c56c70c087cf3 100644 (file)
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1296,7 +1296,7 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
 static irqreturn_t blkif_interrupt(int irq, void *dev_id)
 {
        struct request *req;
-       struct blkif_response *bret;
+       struct blkif_response bret;
        RING_IDX i, rp;
        unsigned long flags;
        struct blkfront_info *info = (struct blkfront_info *)dev_id;
@@ -1316,8 +1316,9 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
        for (i = info->ring.rsp_cons; i != rp; i++) {
                unsigned long id;
 
-               bret = RING_GET_RESPONSE(&info->ring, i);
-               id   = bret->id;
+               RING_COPY_RESPONSE(&info->ring, i, &bret);
+               id   = bret.id;
+
                /*
                 * The backend has messed up and given us an id that we would
                 * never have given to it (we stamp it up to BLK_RING_SIZE -
@@ -1325,29 +1326,29 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
                 */
                if (id >= BLK_RING_SIZE(info)) {
                        WARN(1, "%s: response to %s has incorrect id (%ld)\n",
-                            info->gd->disk_name, op_name(bret->operation), id);
+                            info->gd->disk_name, op_name(bret.operation), id);
                        /* We can't safely get the 'struct request' as
                         * the id is busted. */
                        continue;
                }
                req  = info->shadow[id].request;
 
-               if (bret->operation != BLKIF_OP_DISCARD)
-                       blkif_completion(&info->shadow[id], info, bret);
+               if (bret.operation != BLKIF_OP_DISCARD)
+                       blkif_completion(&info->shadow[id], info, &bret);
 
                if (add_id_to_freelist(info, id)) {
                        WARN(1, "%s: response to %s (id %ld) couldn't be recycled!\n",
-                            info->gd->disk_name, op_name(bret->operation), id);
+                            info->gd->disk_name, op_name(bret.operation), id);
                        continue;
                }
 
-               error = (bret->status == BLKIF_RSP_OKAY) ? 0 : -EIO;
-               switch (bret->operation) {
+               error = (bret.status == BLKIF_RSP_OKAY) ? 0 : -EIO;
+               switch (bret.operation) {
                case BLKIF_OP_DISCARD:
-                       if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
+                       if (unlikely(bret.status == BLKIF_RSP_EOPNOTSUPP)) {
                                struct request_queue *rq = info->rq;
                                printk(KERN_WARNING "blkfront: %s: %s op failed\n",
-                                          info->gd->disk_name, op_name(bret->operation));
+                                          info->gd->disk_name, op_name(bret.operation));
                                error = -EOPNOTSUPP;
                                info->feature_discard = 0;
                                info->feature_secdiscard = 0;
@@ -1358,15 +1359,15 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
                        break;
                case BLKIF_OP_FLUSH_DISKCACHE:
                case BLKIF_OP_WRITE_BARRIER:
-                       if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
+                       if (unlikely(bret.status == BLKIF_RSP_EOPNOTSUPP)) {
                                printk(KERN_WARNING "blkfront: %s: %s op failed\n",
-                                      info->gd->disk_name, op_name(bret->operation));
+                                      info->gd->disk_name, op_name(bret.operation));
                                error = -EOPNOTSUPP;
                        }
-                       if (unlikely(bret->status == BLKIF_RSP_ERROR &&
+                       if (unlikely(bret.status == BLKIF_RSP_ERROR &&
                                     info->shadow[id].req.u.rw.nr_segments == 0)) {
                                printk(KERN_WARNING "blkfront: %s: empty %s op failed\n",
-                                      info->gd->disk_name, op_name(bret->operation));
+                                      info->gd->disk_name, op_name(bret.operation));
                                error = -EOPNOTSUPP;
                        }
                        if (unlikely(error)) {
@@ -1378,9 +1379,9 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
                        /* fall through */
                case BLKIF_OP_READ:
                case BLKIF_OP_WRITE:
-                       if (unlikely(bret->status != BLKIF_RSP_OKAY))
+                       if (unlikely(bret.status != BLKIF_RSP_OKAY))
                                dev_dbg(&info->xbdev->dev, "Bad return from blkdev data "
-                                       "request: %x\n", bret->status);
+                                       "request: %x\n", bret.status);
 
                        blk_mq_complete_request(req, error);
                        break;