From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: -EINTR return in domain_relinquish_resources
Date: Wed, 21 Jan 2015 21:39:46 +0000
Message-ID: <54C01CA2.4090304@citrix.com>
References: <20150121212720.GA24555@l.oracle.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xen.org>
Received: from mail6.bemta14.messagelabs.com ([193.109.254.103])
	by lists.xen.org with esmtp (Exim 4.72)
	(envelope-from <amc96@hermes.cam.ac.uk>) id 1YE307-00009a-Ce
	for xen-devel@lists.xenproject.org; Wed, 21 Jan 2015 21:39:47 +0000
In-Reply-To: <20150121212720.GA24555@l.oracle.com>
List-Unsubscribe: <http://lists.xen.org/cgi-bin/mailman/options/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xen.org>
List-Help: <mailto:xen-devel-request@lists.xen.org?subject=help>
List-Subscribe: <http://lists.xen.org/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=subscribe>
Sender: xen-devel-bounces@lists.xen.org
Errors-To: xen-devel-bounces@lists.xen.org
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, xen-devel@lists.xenproject.org
List-Id: xen-devel@lists.xenproject.org

On 21/01/2015 21:27, Konrad Rzeszutek Wilk wrote:
> As I was looking at some of the XSA I realized that the
> call-chain of:
>
>  domain_relinquish_resources
>    ->vcpu_destroy_pagetables
>      -> put_page_and_type_preemptible
>         -> __put_page_type
> 		returns -EINTR
>
> which means we end up at:
>  618         rc = domain_relinquish_resources(d);                                    
>  619         if ( rc != 0 )                                                          
>  620         {                                                                       
>  621             if ( rc == -ERESTART )                                              
>  622                 rc = -EAGAIN;                                                   
>  623             break;             <=== with rc=-EINTR
>  624         }                                         
>
> And return -EINTR to user-space - which loop in 
> 'xc_domain_destroy' is only looking for:
>
>  112 int xc_domain_destroy(xc_interface *xch,                                        
>  113                       uint32_t domid)                                           
>  114 {                                                                               
>  115     int ret;                                                                    
>  116     DECLARE_DOMCTL;                                                             
>  117     domctl.cmd = XEN_DOMCTL_destroydomain;                                      
>  118     domctl.domain = (domid_t)domid;                                             
>  119     do {                                                                        
>  120         ret = do_domctl(xch, &domctl);                                          
>  121     } while ( ret && (errno == EAGAIN) );                                       
>  122     return ret;                                                                 
>  123 }                                
>
> which to my reading looks like we would exit out and leave
> an DOMDYING_dying domain. Looking at the code it seems possible
> to continue on if the user does 'xl destroy <X>' guest again,
> but I was wondering if:
>
>  a). Should the toolstack (libxl or libxc) have the code to
>      handle -EINTR?
>
>  b). Or should the hypervisor convert the -EINTR to -ERESTART
>      (or -EAGAIN) - which most of the code (see users of
>      get_page_type_preemptible) do right now?

Good spot.

Other areas of similar code condense EINTR into ERESTART.  I think in
this case it is Xen's job to turn -EINTR into -EAGAIN as this hypercall
specifically has preemptibility  built into its normal use.

I wonder if there are other similar hypercall paths which need to catch
EINTR as well as ERESTART?

~Andrew