linux-kernel - Re: [PATCH v3] crypto: remove instance when test failed

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Message-ID: <1948823.Yx9TPYrsU5@tauon>
Date:	Thu, 09 Apr 2015 12:05:14 +0200
From:	Stephan Mueller <smueller@...onox.de>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] crypto: remove instance when test failed

Am Donnerstag, 9. April 2015, 17:40:35 schrieb Herbert Xu:

Hi Herbert,

>On Thu, Apr 09, 2015 at 11:22:19AM +0200, Stephan Mueller wrote:
>> I tested it and this approach does not work.
>> 
>> If I see that right, the reason for that is the following: The suggestion
>> is
>> to grab the ref count at the start of the function followed by a
>> __crypto_register_alg. __crypto_register_alg however sets the refcount to 1
>> unconditionally. That means that the final put of the alg will most likely
>> set the refcount to 0 that causes an issue with all other operations (at
>> least I cannot allocate HMAC or CMAC any more -- the ones I currently
>> test).
>> 
>> So, the grabing of the alg must happen after the invocation of
>> __crypto_register_alg.
>
>Well let's move it then.

Perfect. This now works with the changed patch too. I will resend my patch as 
v4 -- note that this new patch depends on your patch here as otherwise 
instances do not work at all. :-)
>
>---8<---
>crypto: api - Move alg ref count init to crypto_check_alg
>
>We currently initialise the crypto_alg ref count in the function
>__crypto_register_alg.  As one of the callers of that function
>crypto_register_instance needs to obtain a ref count before it
>calls __crypto_register_alg, we need to move the initialisation
>out of there.
>
>Since both callers of __crypto_register_alg call crypto_check_alg,
>this is the logical place to perform the initialisation.
>
>Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

Acked-by: Stephan Mueller <smueller@...onox.de>
>
>diff --git a/crypto/algapi.c b/crypto/algapi.c
>index f1d0307..1462c68 100644
>--- a/crypto/algapi.c
>+++ b/crypto/algapi.c
>@@ -64,6 +64,8 @@ static int crypto_check_alg(struct crypto_alg *alg)
> 	if (alg->cra_priority < 0)
> 		return -EINVAL;
>
>+	atomic_set(&alg->cra_refcnt, 1);
>+
> 	return crypto_set_driver_name(alg);
> }
>
>@@ -187,7 +189,6 @@ static struct crypto_larval *__crypto_register_alg(struct
>crypto_alg *alg)
>
> 	ret = -EEXIST;
>
>-	atomic_set(&alg->cra_refcnt, 1);
> 	list_for_each_entry(q, &crypto_alg_list, cra_list) {
> 		if (q == alg)
> 			goto err;


Ciao
Stephan
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