From: Herbert Xu <herbert@gondor.apana.org.au>
Subject: Re: [PATCH v2 1/4] Wrap crc_t10dif function all to use crypto
 transform framework
Date: Sun, 28 Apr 2013 08:11:22 +0800
Message-ID: <20130428001122.GA6973@gondor.apana.org.au>
References: <cover.1366214842.git.tim.c.chen@linux.intel.com>
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 <20130425132203.GA29501@gondor.apana.org.au>
 <1366910910.27102.126.camel@schen9-DESK>
 <20130426125224.GA4855@gondor.apana.org.au>
 <1366994657.27102.129.camel@schen9-DESK>
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Cc: "H. Peter Anvin" <hpa@zytor.com>,
	"David S. Miller" <davem@davemloft.net>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	James Bottomley <James.Bottomley@HansenPartnership.com>,
	Matthew Wilcox <willy@linux.intel.com>,
	Jim Kukunas <james.t.kukunas@linux.intel.com>,
	Keith Busch <keith.busch@intel.com>,
	Erdinc Ozturk <erdinc.ozturk@intel.com>,
	Vinodh Gopal <vinodh.gopal@intel.com>,
	James Guilford <james.guilford@intel.com>,
	Wajdi Feghali <wajdi.k.feghali@intel.com>,
	Jussi Kivilinna <jussi.kivilinna@iki.fi>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-crypto@vger.kernel.org, linux-scsi@vger.kernel.org
To: Tim Chen <tim.c.chen@linux.intel.com>
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In-Reply-To: <1366994657.27102.129.camel@schen9-DESK>
Sender: linux-crypto-owner@vger.kernel.org

On Fri, Apr 26, 2013 at 09:44:17AM -0700, Tim Chen wrote:
>
> +	old_tfm = crct10dif_tfm;
> +	crc_t10dif_newalg = true;
> +	/* make sure new alg flag is turned on before starting to switch tfm */
> +	mb();
> +
> +	new_tfm = crypto_alloc_shash("crct10dif", 0, 0);
> +	if (IS_ERR(new_tfm))
> +		goto done;
> +
> +	if (old_tfm)
> +		if (crypto_tfm_alg_priority(&old_tfm->base) >=
> +		    crypto_tfm_alg_priority(&new_tfm->base)) {
> +			crypto_free_shash(new_tfm);
> +			goto done;
> +		}
> +	crct10dif_tfm = new_tfm;
> +	/* make sure update to tfm pointer is completed */
> +	mb();
> +	crypto_free_shash(old_tfm);

This is not safe at all.  You'd need to use something like RCU.

However, I think this is an overkill.  Initialising it once should
be enough.  If someone really wanted to change things at run-time,
they could always build this as a module and unload/reload it.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt