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Date:   Wed, 1 Sep 2021 06:30:47 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Luis Chamberlain <mcgrof@kernel.org>, hch@infradead.org,
        linux-block@vger.kernel.org, axboe@kernel.dk
Subject: Re: [PATCH v3 0/8] block: first batch of add_disk() error handling
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On Wed, Sep 01, 2021 at 01:19:44PM +0900, Tetsuo Handa wrote:
> Are the changes by add_disk() made atomically against the caller?
> If there is a moment where "struct block_device_operations"->open can be
> called when add_disk() might still fail, how is it protected from the
> kfree() path?

The new add_disk is structured so tht it won't fail after the block
device inode is hashed.  That is, the last possible failure is before
->open can be called.