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([2a00:79e0:2890:d:9f2c:a127:989c:b6af]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c12b62c552esm710227466b.49.2026.07.06.03.07.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Jul 2026 03:07:29 -0700 (PDT) Message-ID: Date: Mon, 6 Jul 2026 12:07:27 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 01/19] mm/hugetlb: Fix boot panic with CONFIG_DEBUG_VM and HVO bootmem pages To: Muchun Song , Oscar Salvador , David Hildenbrand , Andrew Morton , Madhavan Srinivasan , Michael Ellerman Cc: Muchun Song , Mike Rapoport , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Nicholas Piggin , Christophe Leroy , Ritesh Harjani , "Aneesh Kumar K . V" , linuxppc-dev@lists.ozlabs.org, Mike Kravetz References: <20260612035903.2468601-1-songmuchun@bytedance.com> <20260612035903.2468601-2-songmuchun@bytedance.com> Content-Language: en-US From: =?UTF-8?B?TWljaGHFgiBDxYJhcGnFhHNraQ==?= In-Reply-To: <20260612035903.2468601-2-songmuchun@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 6/12/26 5:58 AM, Muchun Song wrote: > Commit 622026e87c40 ("mm/hugetlb: remove fake head pages") switched > HVO to reuse per-zone shared tail pages from zone->vmemmap_tails[]. > > Those shared tail pages were initialized in hugetlb_vmemmap_init(), but > bootmem HugeTLB folios are prepared earlier from gather_bootmem_prealloc(). > With hugetlb_free_vmemmap=on, prep_and_add_bootmem_folios() can access > pageblock flags on bootmem HugeTLB pages whose mirrored tail struct pages > already point to the shared tail page. On CONFIG_DEBUG_VM kernels, > get_pfnblock_bitmap_bitidx() then dereferences the still-uninitialized > shared tail page and can panic during boot. > > Initialize zone->vmemmap_tails[] from gather_bootmem_prealloc(), before > bootmem HugeTLB folios are processed, and drop the later initialization > from hugetlb_vmemmap_init(). > > This bug only affects CONFIG_DEBUG_VM kernels, where the relevant > assertion is evaluated. > > Fixes: 622026e87c40 ("mm/hugetlb: remove fake head pages") > Signed-off-by: Muchun Song > Acked-by: Oscar Salvador > --- > mm/hugetlb.c | 25 +++++++++++++++++++++++++ > mm/hugetlb_vmemmap.c | 17 ----------------- > mm/sparse-vmemmap.c | 2 +- > 3 files changed, 26 insertions(+), 18 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 571212b80835..cd55524c7e30 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -3365,6 +3365,31 @@ static void __init gather_bootmem_prealloc(void) > .max_threads = num_node_state(N_MEMORY), > .numa_aware = true, > }; > +#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP > + struct zone *zone; > + > + for_each_zone(zone) { > + for (int i = 0; i < NR_VMEMMAP_TAILS; i++) { > + struct page *tail, *p; > + unsigned int order; > + > + tail = zone->vmemmap_tails[i]; > + if (!tail) > + continue; > + > + order = i + VMEMMAP_TAIL_MIN_ORDER; > + p = page_to_virt(tail); > + /* > + * prep_and_add_bootmem_folios() can access pageblock > + * flags on bootmem HugeTLB pages, so initialize the > + * shared tail struct pages here before bootmem folios > + * start using them. > + */ > + for (int j = 0; j < PAGE_SIZE / sizeof(struct page); j++) > + init_compound_tail(p + j, NULL, order, zone); > + } > + } > +#endif I think it would be better if this was located in mm/hugetlb_vmemmap.c as a separate function. > > padata_do_multithreaded(&job); > } > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c > index 133b46dfb09f..c713c0d2593a 100644 > --- a/mm/hugetlb_vmemmap.c > +++ b/mm/hugetlb_vmemmap.c > @@ -870,27 +870,10 @@ static const struct ctl_table hugetlb_vmemmap_sysctls[] = { > static int __init hugetlb_vmemmap_init(void) > { > const struct hstate *h; > - struct zone *zone; > > /* HUGETLB_VMEMMAP_RESERVE_SIZE should cover all used struct pages */ > BUILD_BUG_ON(__NR_USED_SUBPAGE > HUGETLB_VMEMMAP_RESERVE_PAGES); > > - for_each_zone(zone) { > - for (int i = 0; i < NR_VMEMMAP_TAILS; i++) { > - struct page *tail, *p; > - unsigned int order; > - > - tail = zone->vmemmap_tails[i]; > - if (!tail) > - continue; > - > - order = i + VMEMMAP_TAIL_MIN_ORDER; > - p = page_to_virt(tail); > - for (int j = 0; j < PAGE_SIZE / sizeof(struct page); j++) > - init_compound_tail(p + j, NULL, order, zone); > - } > - } > - > for_each_hstate(h) { > if (hugetlb_vmemmap_optimizable(h)) { > register_sysctl_init("vm", hugetlb_vmemmap_sysctls); > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c > index 99e2be39671b..bb23fb3077a3 100644 > --- a/mm/sparse-vmemmap.c > +++ b/mm/sparse-vmemmap.c > @@ -342,7 +342,7 @@ static __meminit struct page *vmemmap_get_tail(unsigned int order, struct zone * > * > * Any initialization done here will be overwritten by memmap_init(). > * > - * hugetlb_vmemmap_init() will take care of initialization after > + * gather_bootmem_prealloc() will take care of initialization after > * memmap_init(). > */ > It gets the job done. Tested-by: Michal Clapinski Reviewed-by: Michal Clapinski