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

[Baokun Li <libaokun@linux.alibaba.com>]

On 2026/10/24 03:38, Eric Biggers wrote:
> 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.
> 

Okay.

>> 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.
> 

That makes sense; I hadn't noticed that difference before.

>> 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.
> 

Yeah, that looks much clearer.

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

Thank you for your review!

I'll send v2 right away.


Cheers,
Baokun