The patch titled Subject: mm/page_alloc: don't call pfn_to_page() on possibly non-existent PFN in split_large_buddy() has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-page_alloc-dont-call-pfn_to_page-on-possibly-non-existent-pfn-in-split_large_buddy.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: David Hildenbrand david@redhat.com Subject: mm/page_alloc: don't call pfn_to_page() on possibly non-existent PFN in split_large_buddy() Date: Tue, 10 Dec 2024 10:34:37 +0100

In split_large_buddy(), we might call pfn_to_page() on a PFN that might not exist. In corner cases, such as when freeing the highest pageblock in the last memory section, this could result with CONFIG_SPARSEMEM && !CONFIG_SPARSEMEM_EXTREME in __pfn_to_section() returning NULL and and __section_mem_map_addr() dereferencing that NULL pointer.

Let's fix it, and avoid doing a pfn_to_page() call for the first iteration, where we already have the page.

So far this was found by code inspection, but let's just CC stable as the fix is easy.

Link: https://lkml.kernel.org/r/20241210093437.174413-1-david@redhat.com Fixes: fd919a85cd55 ("mm: page_isolation: prepare for hygienic freelists") Signed-off-by: David Hildenbrand david@redhat.com Reported-by: Vlastimil Babka vbabka@suse.cz Closes: https://lkml.kernel.org/r/e1a898ba-a717-4d20-9144-29df1a6c8813@suse.cz Reviewed-by: Vlastimil Babka vbabka@suse.cz Reviewed-by: Zi Yan ziy@nvidia.com Acked-by: Johannes Weiner hannes@cmpxchg.org Cc: Yu Zhao yuzhao@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/page_alloc.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-dont-call-pfn_to_page-on-possibly-non-existent-pfn-in-split_large_buddy +++ a/mm/page_alloc.c @@ -1238,13 +1238,15 @@ static void split_large_buddy(struct zon if (order > pageblock_order) order = pageblock_order;

- while (pfn != end) { + do { int mt = get_pfnblock_migratetype(page, pfn);

__free_one_page(page, pfn, zone, order, mt, fpi); pfn += 1 << order; + if (pfn == end) + break; page = pfn_to_page(pfn); - } + } while (1); }

static void free_one_page(struct zone *zone, struct page *page, _

Patches currently in -mm which might be from david@redhat.com are

mm-page_alloc-dont-call-pfn_to_page-on-possibly-non-existent-pfn-in-split_large_buddy.patch docs-tmpfs-update-the-large-folios-policy-for-tmpfs-and-shmem.patch mm-memory_hotplug-move-debug_pagealloc_map_pages-into-online_pages_range.patch mm-page_isolation-dont-pass-gfp-flags-to-isolate_single_pageblock.patch mm-page_isolation-dont-pass-gfp-flags-to-start_isolate_page_range.patch mm-page_alloc-make-__alloc_contig_migrate_range-static.patch mm-page_alloc-sort-out-the-alloc_contig_range-gfp-flags-mess.patch mm-page_alloc-forward-the-gfp-flags-from-alloc_contig_range-to-post_alloc_hook.patch powernv-memtrace-use-__gfp_zero-with-alloc_contig_pages.patch mm-hugetlb-dont-map-folios-writable-without-vm_write-when-copying-during-fork.patch fs-proc-vmcore-convert-vmcore_cb_lock-into-vmcore_mutex.patch fs-proc-vmcore-replace-vmcoredd_mutex-by-vmcore_mutex.patch fs-proc-vmcore-disallow-vmcore-modifications-while-the-vmcore-is-open.patch fs-proc-vmcore-prefix-all-pr_-with-vmcore.patch fs-proc-vmcore-move-vmcore-definitions-out-of-kcoreh.patch fs-proc-vmcore-factor-out-allocating-a-vmcore-range-and-adding-it-to-a-list.patch fs-proc-vmcore-factor-out-freeing-a-list-of-vmcore-ranges.patch fs-proc-vmcore-introduce-proc_vmcore_device_ram-to-detect-device-ram-ranges-in-2nd-kernel.patch virtio-mem-mark-device-ready-before-registering-callbacks-in-kdump-mode.patch virtio-mem-remember-usable-region-size.patch virtio-mem-support-config_proc_vmcore_device_ram.patch s390-kdump-virtio-mem-kdump-support-config_proc_vmcore_device_ram.patch mm-page_alloc-conditionally-split-pageblock_order-pages-in-free_one_page-and-move_freepages_block_isolate.patch mm-page_isolation-fixup-isolate_single_pageblock-comment-regarding-splitting-free-pages.patch mm-page_alloc-dont-use-__gfp_hardwall-when-migrating-pages-via-alloc_contig.patch mm-memory_hotplug-dont-use-__gfp_hardwall-when-migrating-pages-via-memory-offlining.patch