linux-kernel - Re: 4.16-RC7 WARNING: CPU: 2 PID: 0 at block/blk-mq.c:1400 __blk_mq_delay_run_hw

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Date:   Tue, 27 Mar 2018 16:01:21 +0200
From:   Stefan Haberland <sth@...ux.vnet.ibm.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: 4.16-RC7 WARNING: CPU: 2 PID: 0 at block/blk-mq.c:1400
 __blk_mq_delay_run_hw_queue


> This warning is harmless, please try the following patch:
>
> --
>  From 7b2b5139bfef80f44d1b1424e09ab35b715fbfdb Mon Sep 17 00:00:00 2001
> From: Ming Lei <ming.lei@...hat.com>
> Date: Tue, 27 Mar 2018 19:54:23 +0800
> Subject: [PATCH] blk-mq: only run mapped hw queues in blk_mq_run_hw_queues()
>
>  From commit 20e4d813931961fe ("blk-mq: simplify queue mapping & schedule
> with each possisble CPU") on, it should be easier to see unmapped hctx
> in some CPU topo, such as, hctx may not be mapped to any CPU.
>
> This patch avoids the warning in __blk_mq_delay_run_hw_queue() by
> checking if the hctx is mapped in blk_mq_run_hw_queues().
>
> Reported-by: Stefan Haberland <sth@...ux.vnet.ibm.com>
> Cc: Christoph Hellwig <hch@....de>
> Fixes: 20e4d813931961fe ("blk-mq: simplify queue mapping & schedule with each possisble CPU")
> Signed-off-by: Ming Lei <ming.lei@...hat.com>
> ---

Hi Ming,

thanks a lot for the patch. I tried it on top of our 4.16-rc7 branch and 
it works well.
I ran a small regression test set against it and I did not notice any 
warnings or other obvious impacts.

Regards,
Stefan