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Date:   Wed, 15 Sep 2021 15:40:08 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
        "Martin K . Petersen" <martin.petersen@oracle.com>,
        linux-scsi@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
        Sven Schnelle <svens@linux.ibm.com>
Subject: Re: [PATCH] scsi: core: cleanup request queue before releasing
 gendisk
Message-ID: <20210915134008.GA13933@lst.de>
References: <20210915092547.990285-1-ming.lei@redhat.com>
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On Wed, Sep 15, 2021 at 05:25:47PM +0800, Ming Lei wrote:
> gendisk instance has to be released after request queue is cleaned up
> because bdi is referred from gendisk since commit edb0872f44ec ("block:
> move the bdi from the request_queue to the gendisk").
> 
> For sd and sr, gendisk can be removed in the release handler(sd_remove/
> sr_remove) of sdev->sdev_gendev, which is triggered in device_del(sdev->sdev_gendev)
> in __scsi_remove_device(), when the request queue isn't cleaned up yet.
> 
> So kernel oops could be triggered when referring bdi via gendisk.
> 
> Fix the issue by moving blk_cleanup_queue() into sd_remove() and
> sr_remove().

This looks like a bit of a bandaid to me.  I think the proper fix
is to move the parts of blk_cleanup_queue that need a disk or bdi
to del_gendisk.