blk-mq: fix racy updates of rq->errors

blk_mq_complete_request may be a no-op if the request has already
been completed by others means (e.g. a timeout or cancellation), but
currently drivers have to set rq->errors before calling
blk_mq_complete_request, which might leave us with the wrong error value.

Add an error parameter to blk_mq_complete_request so that we can
defer setting rq->errors until we known we won the race to complete the
request.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 10 insertions, 9 deletions

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 0823a96902f8..611170896b8c 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1142,6 +1142,7 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
         RING_IDX i, rp;
         unsigned long flags;
         struct blkfront_info *info = (struct blkfront_info *)dev_id;
+        int error;
 
         spin_lock_irqsave(&info->io_lock, flags);
 
@@ -1182,37 +1183,37 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
                         continue;
                 }
 
-                req->errors = (bret->status == BLKIF_RSP_OKAY) ? 0 : -EIO;
+                error = (bret->status == BLKIF_RSP_OKAY) ? 0 : -EIO;
                 switch (bret->operation) {
                 case BLKIF_OP_DISCARD:
                         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));
-                                req->errors = -EOPNOTSUPP;
+                                error = -EOPNOTSUPP;
                                 info->feature_discard = 0;
                                 info->feature_secdiscard = 0;
                                 queue_flag_clear(QUEUE_FLAG_DISCARD, rq);
                                 queue_flag_clear(QUEUE_FLAG_SECDISCARD, rq);
                         }
-                        blk_mq_complete_request(req);
+                        blk_mq_complete_request(req, error);
                         break;
                 case BLKIF_OP_FLUSH_DISKCACHE:
                 case BLKIF_OP_WRITE_BARRIER:
                         if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
                                 printk(KERN_WARNING "blkfront: %s: %s op failed\n",
                                        info->gd->disk_name, op_name(bret->operation));
-                                req->errors = -EOPNOTSUPP;
+                                error = -EOPNOTSUPP;
                         }
                         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));
-                                req->errors = -EOPNOTSUPP;
+                                error = -EOPNOTSUPP;
                         }
-                        if (unlikely(req->errors)) {
-                                if (req->errors == -EOPNOTSUPP)
-                                        req->errors = 0;
+                        if (unlikely(error)) {
+                                if (error == -EOPNOTSUPP)
+                                        error = 0;
                                 info->feature_flush = 0;
                                 xlvbd_flush(info);
                         }
@@ -1223,7 +1224,7 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
                                 dev_dbg(&info->xbdev->dev, "Bad return from blkdev data "
                                         "request: %x\n", bret->status);
 
-                        blk_mq_complete_request(req);
+                        blk_mq_complete_request(req, error);
                         break;
                 default:
                         BUG();