blk-mq: fix dereference of rq->mq_ctx if allocation fails

If __GFP_WAIT isn't set and we fail allocating, when we go
to drop the reference on the ctx, we will attempt to dereference
the NULL rq. Fix that.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 8 insertions, 4 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index cdc629cf075b..70fd6f996600 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -202,10 +202,12 @@ static struct request *blk_mq_alloc_request_pinned(struct request_queue *q,
                 if (rq) {
                         blk_mq_rq_ctx_init(q, ctx, rq, rw);
                         break;
-                } else if (!(gfp & __GFP_WAIT))
-                        break;
+                }
 
                 blk_mq_put_ctx(ctx);
+                if (!(gfp & __GFP_WAIT))
+                        break;
+
                 __blk_mq_run_hw_queue(hctx);
                 blk_mq_wait_for_tags(hctx->tags);
         } while (1);
@@ -222,7 +224,8 @@ struct request *blk_mq_alloc_request(struct request_queue *q, int rw,
                 return NULL;
 
         rq = blk_mq_alloc_request_pinned(q, rw, gfp, reserved);
-        blk_mq_put_ctx(rq->mq_ctx);
+        if (rq)
+                blk_mq_put_ctx(rq->mq_ctx);
         return rq;
 }
 
@@ -235,7 +238,8 @@ struct request *blk_mq_alloc_reserved_request(struct request_queue *q, int rw,
                 return NULL;
 
         rq = blk_mq_alloc_request_pinned(q, rw, gfp, true);
-        blk_mq_put_ctx(rq->mq_ctx);
+        if (rq)
+                blk_mq_put_ctx(rq->mq_ctx);
         return rq;
 }
 EXPORT_SYMBOL(blk_mq_alloc_reserved_request);