linux-kernel - Re: [PATCH 1/3] fixup! mm: always initialise folio->_deferred

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Date: Thu, 18 Apr 2024 00:46:39 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Peter Xu <peterx@...hat.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	David Hildenbrand <david@...hat.com>,
	Mina Almasry <almasrymina@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Muchun Song <muchun.song@...ux.dev>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH 1/3] fixup! mm: always initialise folio->_deferred_list

On Wed, Apr 17, 2024 at 05:18:34PM -0400, Peter Xu wrote:
> Current mm-unstable will hit this when running test_hugetlb_memcg.  This
> fixes the crash for me.
> 
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>  mm/memcontrol.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 1840ba4c355d..7703ced535a3 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -7529,6 +7529,7 @@ static void uncharge_folio(struct folio *folio, struct uncharge_gather *ug)
>  
>  	VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
>  	VM_BUG_ON_FOLIO(folio_order(folio) > 1 &&
> +			!folio_test_hugetlb(folio) &&
>  			!list_empty(&folio->_deferred_list), folio);

Hum.  I thought we didn't get here for hugetlb folios.  What
stacktrace did you get?

I'm basing it on comments like this:

                /* hugetlb has its own memcg */
                if (folio_test_hugetlb(folio)) {
                        if (lruvec) {
                                unlock_page_lruvec_irqrestore(lruvec, flags);
                                lruvec = NULL;
                        }
                        free_huge_folio(folio);
                        continue;
                }