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From: Jens Axboe <axboe@fb.com>
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On 10/26/2016 05:08 PM, Linus Torvalds wrote:
> On Wed, Oct 26, 2016 at 4:03 PM, Jens Axboe <axboe@fb.com> wrote:
>>
>> Actually, I think I see what might trigger it. You are on nvme, iirc,
>> and that has a deep queue.
>
> Yes. I have long since moved on from slow disks, so all my systems are
> not just flash, but m.2 nvme ssd's.
>
> So at least that could explain why Dave sees it at bootup but I don't.

Yep, you'd never sleep during normal boot. The original patch had a
problem, though... This one should be better. Too many 'data's, we'll
still need to assign ctx/hctx, we should just use the current ones, not
the original ones.

diff --git a/block/blk-mq.c b/block/blk-mq.c
index ddc2eed64771..e56fec187ba6 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1217,9 +1224,9 @@ static struct request *blk_mq_map_request(struct 
request_queue *q,
  	blk_mq_set_alloc_data(&alloc_data, q, 0, ctx, hctx);
  	rq = __blk_mq_alloc_request(&alloc_data, op, op_flags);

-	hctx->queued++;
-	data->hctx = hctx;
-	data->ctx = ctx;
+	data->hctx = alloc_data.hctx;
+	data->ctx = alloc_data.ctx;
+	data->hctx->queued++;
  	return rq;
  }


-- 
Jens Axboe