Re: [PATCH v6 2/8] hugetlb: restructure pool allocations

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 9 Oct 2023 08:15:13 -0700 Mike Kravetz <mike.kravetz@oracle.com> wrote:

> > This should also be empty and a noop.
> > 
> > Is it possible that the misaligned kernel image could make these lists
> > appear as non-empty?
> 
> Actually, just saw this:
> 
> https://lore.kernel.org/linux-mm/20231009145605.2150897-1-usama.arif@bytedance.com/
> 
> Will take a look, although as mentioned above prep_and_add_bootmem_folios on
> an empty list should be a noop.

Konrad, are you able to test Usama's patch?  Thanks.

From: Usama Arif <usama.arif@bytedance.com>
Subject: mm: hugetlb: only prep and add allocated folios for non-gigantic pages
Date: Mon, 9 Oct 2023 15:56:05 +0100

Calling prep_and_add_allocated_folios when allocating gigantic pages at
boot time causes the kernel to crash as folio_list is empty and iterating
it causes a NULL pointer dereference.  Call this only for non-gigantic
pages when folio_list has entries.

Link: https://lkml.kernel.org/r/20231009145605.2150897-1-usama.arif@bytedance.com
Fixes: bfb41d6b2fe148 ("hugetlb: restructure pool allocations")
Signed-off-by: Usama Arif <usama.arif@bytedance.com>
Cc: Fam Zheng <fam.zheng@bytedance.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Barry Song <21cnbao@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Konrad Dybcio <konradybcio@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/hugetlb.c~hugetlb-restructure-pool-allocations-fix
+++ a/mm/hugetlb.c
@@ -3307,7 +3307,8 @@ static void __init hugetlb_hstate_alloc_
 	}
 
 	/* list will be empty if hstate_is_gigantic */
-	prep_and_add_allocated_folios(h, &folio_list);
+	if (!hstate_is_gigantic(h))
+		prep_and_add_allocated_folios(h, &folio_list);
 
 	if (i < h->max_huge_pages) {
 		char buf[32];
_