From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v13 05/10] x86: dynamically attach/detach
 QoS monitoring service for a guest
Date: Mon, 4 Aug 2014 10:38:09 +0100
Message-ID: <53DF5481.3010207@citrix.com>
References: <1407118626-76843-1-git-send-email-dongxiao.xu@intel.com>
	<1407118626-76843-6-git-send-email-dongxiao.xu@intel.com>
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To: Dongxiao Xu <dongxiao.xu@intel.com>, xen-devel@lists.xen.org
Cc: keir@xen.org, Ian.Campbell@citrix.com, George.Dunlap@eu.citrix.com, stefano.stabellini@eu.citrix.com, Ian.Jackson@eu.citrix.com, JBeulich@suse.com, dgdegra@tycho.nsa.gov
List-Id: xen-devel@lists.xenproject.org

On 04/08/14 03:17, Dongxiao Xu wrote:
> +/* Called with domain lock held, no pqos specific lock needed */
> +int pqos_monitor_alloc_rmid(struct domain *d)
> +{
> +    unsigned int rmid;
> +
> +    ASSERT(pqos_monitor_enabled());
> +
> +    if ( d->arch.pqos_rmid > 0 )
> +        return -EEXIST;
> +
> +    for ( rmid = pqosm->rmid_min; rmid <= pqosm->rmid_max; rmid++ )
> +    {
> +        if ( pqosm->rmid_to_dom[rmid] != DOMID_INVALID)
> +            continue;
> +
> +        pqosm->rmid_to_dom[rmid] = d->domain_id;
> +        break;
> +    }
> +
> +    /* No RMID available, assign RMID=0 by default */
> +    if ( rmid > pqosm->rmid_max )
> +    {
> +        d->arch.pqos_rmid = 0;
> +        return -EUSERS;
> +    }
> +    else
> +        pqosm->rmid_inuse++;

This rmid_inuse needs some concurrency protection; the domain lock is
not suitable.  Probably best to make it an atomic_t and use atomic_inc/dec()

~Andrew