linux-kernel - Re: [PATCH] mm/hugetlb: fix gigantic page initialization/allocation

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Date:	Tue, 2 Feb 2016 15:17:10 -0800
From:	Mike Kravetz <mike.kravetz@...cle.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Jerome Marchand <jmarchan@...hat.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: [PATCH] mm/hugetlb: fix gigantic page initialization/allocation

On 02/02/2016 02:59 PM, David Rientjes wrote:
> On Tue, 2 Feb 2016, Mike Kravetz wrote:
> 
>> Attempting to preallocate 1G gigantic huge pages at boot time with
>> "hugepagesz=1G hugepages=1" on the kernel command line will prevent
>> booting with the following:
>>
>> kernel BUG at mm/hugetlb.c:1218!
>>
>> When mapcount accounting was reworked, the setting of compound_mapcount_ptr
>> in prep_compound_gigantic_page was overlooked.  As a result, the validation
>> of mapcount in free_huge_page fails.
>>
>> The "BUG_ON" checks in free_huge_page were also changed to "VM_BUG_ON_PAGE"
>> to assist with debugging.
>>
>> Fixes: af5642a8af ("mm: rework mapcount accounting to enable 4k mapping of THPs")
>> Suggested-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
>> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> 
> I'm not sure whether this should have a "From: Naoya Horiguchi" line with 
> an accompanying sign-off or not, since Naoya debugged and wrote the actual 
> fix to prep_compound_gigantic_page().

I agree.  Naoya did debug and provide fix via e-mail exchange.  He did not
sign-off and I could not tell if he was going to pursue.  My only intention
was to fix ASAP.

More than happy to give Naoya credit.
-- 
Mike Kravetz

> 
> Acked-by: David Rientjes <rientjes@...gle.com>
>