linux-kernel - Re: [PATCH] mm/hugetlb.c: fix a bug within a BUG(): inconsistent pte comparison

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Date:   Fri, 30 Jun 2023 17:21:56 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Ryan Roberts <ryan.roberts@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     LKML <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alex Williamson <alex.williamson@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        "Christian Brauner" <brauner@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Daniel Vetter" <daniel@...ll.ch>, Dave Airlie <airlied@...il.com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Ian Rogers <irogers@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>, Jiri Olsa <jolsa@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
        Muchun Song <muchun.song@...ux.dev>,
        Namhyung Kim <namhyung@...nel.org>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        "Oleksandr Tyshchenko" <oleksandr_tyshchenko@...m.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        SeongJae Park <sj@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        "Uladzislau Rezki" <urezki@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        "Yu Zhao" <yuzhao@...gle.com>
Subject: Re: [PATCH] mm/hugetlb.c: fix a bug within a BUG(): inconsistent pte
 comparison

On 6/30/23 03:07, Ryan Roberts wrote:
...
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index bce28cca73a1..73fbeb8f979f 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -7246,7 +7246,12 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
>>   				pte = (pte_t *)pmd_alloc(mm, pud, addr);
>>   		}
>>   	}
>> -	BUG_ON(pte && pte_present(ptep_get(pte)) && !pte_huge(ptep_get(pte)));
>> +
>> +	if (pte) {
>> +		pte_t pteval = ptep_get(pte);
> 
> Given the PTL is not held here, I think this should technically be
> ptep_get_lockless()?
> 

Oh yes. I'll change it to that and send a v2, thanks!


thanks,
-- 
John Hubbard
NVIDIA