[PATCH 04/12] block: Requeue requests if a CPU is unplugged

[Bart Van Assche <bvanassche@xxxxxxx>]

Requeue requests instead of sending these to the dispatch list if a CPU
is unplugged to prevent reordering of zoned writes.

Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
 block/blk-mq.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f6ffa76bc159..8bb35deff5ec 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3496,9 +3496,17 @@ static int blk_mq_hctx_notify_dead(unsigned int cpu, struct hlist_node *node)
 	if (list_empty(&tmp))
 		return 0;
 
-	spin_lock(&hctx->lock);
-	list_splice_tail_init(&tmp, &hctx->dispatch);
-	spin_unlock(&hctx->lock);
+	if (hctx->queue->elevator) {
+		struct request *rq, *next;
+
+		list_for_each_entry_safe(rq, next, &tmp, queuelist)
+			blk_mq_requeue_request(rq, false);
+		blk_mq_kick_requeue_list(hctx->queue);
+	} else {
+		spin_lock(&hctx->lock);
+		list_splice_tail_init(&tmp, &hctx->dispatch);
+		spin_unlock(&hctx->lock);
+	}
 
 	blk_mq_run_hw_queue(hctx, true);
 	return 0;