linux-kernel - Re: s390 boot woe due to "block: fix busy device checking in blk_drop

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Message-ID: <20200423110738.GA102241@blackbook>
Date:   Thu, 23 Apr 2020 13:07:38 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Qian Cai <cai@....pw>, Jens Axboe <axboe@...nel.dk>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        linux-block@...r.kernel.org, linux-s390@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: s390 boot woe due to "block: fix busy device checking in
 blk_drop_partitions"

Hi.

On Fri, Apr 10, 2020 at 07:45:44AM +0200, Christoph Hellwig <hch@....de> wrote:
> @@ -496,7 +496,7 @@ int blk_drop_partitions(struct gendisk *disk, struct block_device *bdev)
> -	if (bdev->bd_part_count || bdev->bd_openers)
> +	if (bdev->bd_part_count || bdev->bd_openers > 1)
>  		return -EBUSY;
I noticed this (and the previous patch) change unmasks race between
ioctl(LOOP_SET_STATUS64, ... lo_flags=LO_FLAGS_PARTSCAN ...) and udev
processing loop device uevents. See [1] for details.

Should the condition be changed in the case of newly setup loop devices?
(Or shouldn't the ioctl propagate EBUSY in its return value?)

Thanks,
Michal

[1] https://bugzilla.opensuse.org/show_bug.cgi?id=1169932

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