blk-mq: enable IO poll if .nr_queues of type poll > 0

The queue mapping of type poll only exists when set->map[HCTX_TYPE_POLL].nr_queues
is bigger than zero, so enhance the constraint by checking .nr_queues of type poll
before enabling IO poll.

Otherwise IO race & timeout can be observed when running block/007.

Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 2 insertions, 1 deletions

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index bb7c642ffefa..0619c8922893 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -402,7 +402,8 @@ static ssize_t queue_poll_store(struct request_queue *q, const char *page,
         unsigned long poll_on;
         ssize_t ret;
 
-        if (!q->tag_set || q->tag_set->nr_maps <= HCTX_TYPE_POLL)
+        if (!q->tag_set || q->tag_set->nr_maps <= HCTX_TYPE_POLL ||
+            !q->tag_set->map[HCTX_TYPE_POLL].nr_queues)
                 return -EINVAL;
 
         ret = queue_var_store(&poll_on, page, count);