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Date:   Wed, 6 Sep 2023 18:10:24 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Mikulas Patocka <mpatocka@redhat.com>
Cc:     Christian Brauner <brauner@kernel.org>,
        Zdenek Kabelac <zkabelac@redhat.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        dm-devel@redhat.com, Jan Kara <jack@suse.cz>,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] fix writing to the filesystem after unmount
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On Wed, Sep 06, 2023 at 06:01:06PM +0200, Mikulas Patocka wrote:

> Perhaps we could distinguish between FIFREEZE-initiated freezes and 
> device-mapper initiated freezes as well. And we could change the logic to 
> return -EBUSY if the freeze was initiated by FIFREEZE and to wait for 
> unfreeze if it was initiated by the device-mapper.

By the time you get to cleanup_mnt() it's far too late to return -EBUSY.