From: Mimi Zohar <zohar@linux.ibm.com>
Date: Fri, 13 Dec 2019 02:32:57 +0000
Subject: Re: [PATCH v3 1/2] IMA: Define workqueue for early boot "key" measurements
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References: <20191213004250.21132-1-nramas@linux.microsoft.com>
         <20191213004250.21132-2-nramas@linux.microsoft.com>
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In-Reply-To: <6e0dad33-66f9-4807-d08d-ff30396cec5e@linux.microsoft.com>
To: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>, linux-integrity@vger.kernel.org
Cc: eric.snowberg@oracle.com, dhowells@redhat.com, mathew.j.martineau@linux.intel.com, matthewgarrett@google.com, sashal@kernel.org, jamorris@linux.microsoft.com, linux-kernel@vger.kernel.org, keyrings@vger.kernel.org

On Thu, 2019-12-12 at 17:59 -0800, Lakshmi Ramasubramanian wrote:
> On 12/12/19 5:55 PM, Mimi Zohar wrote:
> >> +/*
> >> + * ima_process_queued_keys() - process keys queued for measurement
> >> + *
> >> + * This function sets ima_process_keys to true and processes queued keys.
> >> + * From here on keys will be processed right away (not queued).
> >> + */
> >> +void ima_process_queued_keys(void)
> >> +{
> >> +	struct ima_key_entry *entry, *tmp;
> >> +	LIST_HEAD(temp_ima_keys);
> >> +
> >> +	if (ima_process_keys)
> >> +		return;
> >> +
> >> +	/*
> >> +	 * To avoid holding the mutex when processing queued keys,
> >> +	 * transfer the queued keys with the mutex held to a temp list,
> >> +	 * release the mutex, and then process the queued keys from
> >> +	 * the temp list.
> >> +	 *
> >> +	 * Since ima_process_keys is set to true, any new key will be
> >> +	 * processed immediately and not be queued.
> >> +	 */
> >> +	INIT_LIST_HEAD(&temp_ima_keys);
> >> +
> >> +	mutex_lock(&ima_keys_mutex);
> > 
> > Don't you need a test here, before setting ima_process_keys?
> > 
> > 	if (ima_process_keys)
> > 		return;
> > 
> > Mimi
> 
> That check is done before the comment - at the start of 
> ima_process_queued_keys().

The first test prevents taking the mutex unnecessarily.

Mimi


> +void ima_process_queued_keys(void)
> +{
> +	struct ima_key_entry *entry, *tmp;
> +	LIST_HEAD(temp_ima_keys);
> +
> +	if (ima_process_keys)
> +		return;
> 
> thanks,
>   -lakshmi