Re: [PATCH v4 03/10] IOMMU/MMU: enhance the call trees of IOMMU unmapping and mapping

From: "Jan Beulich" <JBeulich@suse.com>
To: Quan Xu <quan.xu@intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>, Keir Fraser <keir@xen.org>,
	George Dunlap <george.dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	"dario.faggioli@citrix.com" <dario.faggioli@citrix.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
	Jun Nakajima <jun.nakajima@intel.com>
Subject: Re: [PATCH v4 03/10] IOMMU/MMU: enhance the call trees of IOMMU unmapping and mapping
Date: Wed, 11 May 2016 01:02:04 -0600	[thread overview]
Message-ID: <5732F50C02000078000EA664@prv-mh.provo.novell.com> (raw)
In-Reply-To: <945CA011AD5F084CBEA3E851C0AB28894B8AC758@SHSMSX101.ccr.corp.intel.com>

>>> On 11.05.16 at 05:39, <quan.xu@intel.com> wrote:
> On May 10, 2016 4:44 PM, Jan Beulich <JBeulich@suse.com> wrote:
>> >>> On 06.05.16 at 10:54, <quan.xu@intel.com> wrote:
>> > --- a/xen/arch/x86/mm/p2m.c
>> > +++ b/xen/arch/x86/mm/p2m.c
>> > @@ -638,13 +638,20 @@ p2m_remove_page(struct p2m_domain *p2m,
>> unsigned long gfn, unsigned long mfn,
>> >      mfn_t mfn_return;
>> >      p2m_type_t t;
>> >      p2m_access_t a;
>> > +    int rc = 0, ret;
>> >
>> >      if ( !paging_mode_translate(p2m->domain) )
>> >      {
>> >          if ( need_iommu(p2m->domain) )
>> >              for ( i = 0; i < (1 << page_order); i++ )
>> > -                iommu_unmap_page(p2m->domain, mfn + i);
>> > -        return 0;
>> > +            {
>> > +               ret = iommu_unmap_page(p2m->domain, mfn + i);
>> > +
>> > +               if ( !rc )
>> > +                   rc = ret;
>> > +            }
>> > +
>> > +        return rc;
>> >      }
>> 
>> In code like this, btw., restricting the scope of "ret" to the innermost 
> block
>> would help future readers see immediately that the value of "ret" is of no
>> further interest outside of that block.
>> 
>> Having reached the end of the patch, I'm missing the __must_check additions
>> that you said you would do in this new iteration. Is there any reason for 
> their
>> absence? Did I overlook something?
>> 
> 
> Sorry, I did overlook something.
> Checked the v2/v3 replies again, I still can't find it.
> I only add the __must_check annotation for these functions you point out.

Okay, that's the problem then: When we discussed this originally
(in abstract terms) I had clearly said that all involved functions
should become __must_check ones to make sure all cases get
caught where so far error returns got ignored. And on that basis
(as well as on the common grounds that I try to avoid repeating
the same comment over and over when reviewing a patch or a
series of patches) you should have determined yourself the full
set of functions needing the annotation. The rule of thumb is: If
a function calls a __must_check one and doesn't itself consume
the return value, it should also obtain __must_check.

> Do I need to add the __must_check annotation for these  functions (but not 
> void function) in this patch?

IOW - yes. And you'll need to apply the same consideration to
most (all?) other patches in this series.

Jan

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel