[PATCH 1/8] blk-mq: make sure that correct hctx->next_cpu is set

[Ming Lei]

>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: Christian Borntraeger <borntrae...@de.ibm.com>
Cc: Christoph Hellwig <h...@lst.de>
Cc: Stefan Haberland <s...@linux.vnet.ibm.com>
Fixes: 20e4d81393196 ("blk-mq: simplify queue mapping & schedule with each 
possisble CPU")
Cc: sta...@vger.kernel.org
Signed-off-by: Ming Lei <ming....@redhat.com>
---
 block/blk-mq.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f5c7dbcb954f..9b220dc415ac 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2432,6 +2432,8 @@ 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;
        }
 }
-- 
2.9.5