blk-mq: make sure that correct hctx->next_cpu is set

From commit 20e4d81393196 (blk-mq: simplify queue mapping & schedule
with each possisble CPU), one hctx can be mapped from all offline CPUs,
then hctx->next_cpu can be set as wrong.

This patch fixes this issue by making hctx->next_cpu pointing to the
first CPU in hctx->cpumask if all CPUs in hctx->cpumask are offline.

Cc: Stefan Haberland <sth@linux.vnet.ibm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Fixes: 20e4d81393196 ("blk-mq: simplify queue mapping & schedule with each possisble CPU")
Cc: stable@vger.kernel.org
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 2 insertions, 0 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 90f869a083a4..f489ec920807 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2431,6 +2431,8 @@ static void blk_mq_map_swqueue(struct request_queue *q)
                  */
                 hctx->next_cpu = cpumask_first_and(hctx->cpumask,
                                 cpu_online_mask);
+                if (hctx->next_cpu >= nr_cpu_ids)
+                        hctx->next_cpu = cpumask_first(hctx->cpumask);
                 hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
         }
 }