blk-mq: check q->poll_stat in queue_poll_stat_show

Without checking q->poll_stat in queue_poll_stat_show(), kernel panic
may be caused if q->poll_stat isn't allocated.

Fixes: 48b5c1fbcd8c ("block: only allocate poll_stats if there's a user of them")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20211202090716.3292244-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 7f27dca..3a790eb 100644 (file)
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -30,6 +30,9 @@ static int queue_poll_stat_show(void *data, struct seq_file *m)
        struct request_queue *q = data;
        int bucket;
 
+       if (!q->poll_stat)
+               return 0;
+
        for (bucket = 0; bucket < (BLK_MQ_POLL_STATS_BKTS / 2); bucket++) {
                seq_printf(m, "read  (%d Bytes): ", 1 << (9 + bucket));
                print_stat(m, &q->poll_stat[2 * bucket]);