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Date:   Tue, 29 Mar 2022 15:25:02 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc:     Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        Josef Bacik <josef@toxicpanda.com>,
        Minchan Kim <minchan@kernel.org>,
        Nitin Gupta <ngupta@vflare.org>, Jan Kara <jack@suse.cz>,
        "Darrick J . Wong" <djwong@kernel.org>,
        Ming Lei <ming.lei@redhat.com>,
        Matteo Croce <mcroce@microsoft.com>,
        linux-block@vger.kernel.org, nbd@other.debian.org
Subject: Re: [PATCH 13/14] loop: remove lo_refcount and avoid lo_mutex in
 ->open / ->release
Message-ID: <20220329132502.GA2024@lst.de>
References: <20220325063929.1773899-1-hch@lst.de> <20220325063929.1773899-14-hch@lst.de> <03628e13-ca56-4ed0-da5a-ee698c83f48d@I-love.SAKURA.ne.jp> <20220329065234.GA20006@lst.de>
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Thinking a bit more, I really don't think the existing any refcount
check protects us against a different tread modififying the backing
file.  When a process has a file descriptor to a loop device open
and is multithreaded (or forks) we can still have multiple threads
manipulating the loop state.

That being said I do not think we really need that refcount check
at all - once loop_clr_fd set lo->lo_state to Lo_rundown under the
global lock we know that loop_validate_file will error out on it
due to the lo_state != Lo_bound check.