linux-kernel - Re: [PATCH v8 17/18] scsi: megaraid_sas: Added support for shared host tagset for cpuhotplug

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Date:   Wed, 11 Nov 2020 23:04:21 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Qian Cai <cai@...hat.com>
Cc:     Sumit Saxena <sumit.saxena@...adcom.com>,
        John Garry <john.garry@...wei.com>,
        Kashyap Desai <kashyap.desai@...adcom.com>,
        Jens Axboe <axboe@...nel.dk>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        don.brace@...rosemi.com, Bart Van Assche <bvanassche@....org>,
        dgilbert@...erlog.com, paolo.valente@...aro.org,
        Hannes Reinecke <hare@...e.de>, Christoph Hellwig <hch@....de>,
        linux-block@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux SCSI List <linux-scsi@...r.kernel.org>,
        esc.storagedev@...rosemi.com,
        "PDL,MEGARAIDLINUX" <megaraidlinux.pdl@...adcom.com>,
        chenxiang66@...ilicon.com, luojiaxing@...wei.com,
        Hannes Reinecke <hare@...e.com>
Subject: Re: [PATCH v8 17/18] scsi: megaraid_sas: Added support for shared
 host tagset for cpuhotplug

On Wed, Nov 11, 2020 at 09:42:17AM -0500, Qian Cai wrote:
> On Wed, 2020-11-11 at 17:27 +0800, Ming Lei wrote:
> > Can this issue disappear by applying the following change?
> 
> This makes the system boot again as well.

OK, actually it isn't necessary to register one new lock key for each
hctx(blk_flush_queue) instance, and the current way is really over-kill
because there can be lots of hw queues in one system.

The original lockdep warning can be avoided by setting one nvme_loop
specific lock class simply. If nvme_loop is backed against another nvme_loop,
we still can avoid the warning by killing the direct end io chain, or
assign another lock class.

Will prepare one formal patch tomorrow.

Thanks,
Ming