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Date: Wed, 27 Dec 2023 11:09:03 -0600
From: Eric Biggers <ebiggers@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
	David Sterba <dsterba@suse.com>, linux-btrfs@vger.kernel.org,
	Christian Brauner <brauner@kernel.org>
Subject: Re: [PATCH 2/5] btrfs: call btrfs_close_devices from ->kill_sb
Message-ID: <20231227170903.GA1144@quark.localdomain>
References: <20231218044933.706042-1-hch@lst.de>
 <20231218044933.706042-3-hch@lst.de>
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In-Reply-To: <20231218044933.706042-3-hch@lst.de>

On Mon, Dec 18, 2023 at 05:49:30AM +0100, Christoph Hellwig wrote:
> blkdev_put must not be called under sb->s_umount to avoid a lock order
> reversal with disk->open_mutex once call backs from block devices to
> the file system using the holder ops are supported.

This contradicts the following from Documentation/filesystems/porting.rst:

    **mandatory**

    Lock ordering has been changed so that s_umount ranks above open_mutex again.
    All places where s_umount was taken under open_mutex have been fixed up.

So the rationale for this patch seems off.

It's still needed as a prerequisite for "fs: move fscrypt keyring destruction to
after ->put_super", if we indeed go with that instead of the alternative patch
"fscrypt: move the call to fscrypt_destroy_keyring() into ->put_super()".

- Eric