Re: [PATCH v3] fscrypt: Fix missing barrier in fscrypt_find_mode_key()

[Eric Biggers <ebiggers@kernel.org>]

On Sat, Oct 24, 2026 at 12:07:47AM +0800, Baokun Li wrote:
> dm-inlinecrypt reaches its key only through srcu_dereference(md->map),
> with no acquire anywhere on the I/O path.

The above seems like a stray sentence that should be deleted.

> Suggested-by: Eric Biggers <ebiggers@kernel.org>
> Link: https://patch.msgid.link/20261014161153.GC322435@quark

Nit: lore.kernel.org instead of patch.msgid.link, since it links to a
discussion (in response to a patch) rather than directly to a patch.

> diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
> index 892044ebcaca..984ef43982a3 100644
> --- a/fs/crypto/keysetup.c
> +++ b/fs/crypto/keysetup.c
> @@ -205,8 +205,14 @@ fscrypt_find_mode_key(struct fscrypt_master_key *mk, u8 hkdf_context,
>  		if (node->hkdf_context == hkdf_context &&
>  		    node->mode_num == mode_num &&
>  		    node->data_unit_bits == ci->ci_data_unit_bits &&
> -		    fscrypt_is_key_prepared(&node->key, ci))
> +		    fscrypt_is_key_prepared(&node->key, ci)) {
> +			/*
> +			 * Pairs with list_add_tail_rcu() in
> +			 * setup_per_mode_enc_key().
> +			 */
> +			smp_acquire__after_ctrl_dep();
>  			return &node->key;
> +		}
>  	}

I think a better comment would be:

			/*
			 * Upgrade the RCU dereference to a full ACQUIRE, so
			 * that blk-crypto global state is seen as initialized.
			 */

That helps convey why the pre-existing RCU dereference isn't enough.

Other than that this patch looks good.  I can fix all the above when
applying, if you agree, or you can just resend.  Thanks!

- Eric