Re: [Xen-devel] [PATCH for-4.9] x86/mm: Placate DEADCODE Coverity warning

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.06.17 at 13:09, <julien.grall@xxxxxxx> wrote:
> Hi Andrew,
> 
> On 31/05/17 14:23, Andrew Cooper wrote:
>> On 31/05/17 09:52, Julien Grall wrote:
>>> Hi,
>>>
>>> On 05/22/2017 02:32 PM, Jan Beulich wrote:
>>>>>>> On 22.05.17 at 15:12, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>>> _PAGE_GNTTAB is only used in debug builds of Xen; in release builds,
>>>>> it has
>>>>> the value 0.  Coverity complains that "l1e_get_flags(l1e) & 0" is
>>>>> logically
>>>>> dead.
>>>>>
>>>>> Add an extra condition into the logic to skip the flag check if
>>>>> _PAGE_GNTTAB
>>>>> is 0.
>>>>
>>>> And this helps? To me "if ( 0 && ... )" and "if ( (x & 0) && ... )" look
>>>> logically the same (i.e. I'd expect the same warnings to be triggered
>>>> [or not]).
>>>
>>> I haven't seen any answer on this question. Andrew, does this patch
>>> still hold for Xen 4.9?
>>
>> Sorry - it fell through the cracks, but yes, it does stand for 4.9.
>>
>> As to the "if ( 0 && ... )" and "if ( (x & 0) && ... )", one is very
>> clearly a "short circuit every thing else if this value is zero", while
>> the other looks like a programming mistake, which is also why I expect
>> this to resolve Coverity's complaint.
>>
>> Unfortunately, I can't be certain that this will resolve the issue until
>> it gets committed, as I don't have a useful way to run Coverity on
>> arbitrary non-debug builds.
> 
> Are we running staging-4.* branch on Coverity? Looking at the git, I see 
> *coverity* branch only on unstable.

Yes, so my suggestion would be to commit the patch on master, see
if it helps, and if so consider backporting for 4.9. If it doesn't help,
it should be reverted or replaced by something "better".

Jan


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