From: Jinjiang Tu Date: Fri, 27 Jun 2025 12:57:46 +0000 (+0800) Subject: mm/vmscan: fix hwpoisoned large folio handling in shrink_folio_list X-Git-Tag: v6.16~11^2~10 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9f1e8cd0b7c4c944e9921b52a6661b5eda2705ab;p=thirdparty%2Fkernel%2Fstable.git mm/vmscan: fix hwpoisoned large folio handling in shrink_folio_list In shrink_folio_list(), the hwpoisoned folio may be large folio, which can't be handled by unmap_poisoned_folio(). For THP, try_to_unmap_one() must be passed with TTU_SPLIT_HUGE_PMD to split huge PMD first and then retry. Without TTU_SPLIT_HUGE_PMD, we will trigger null-ptr deref of pvmw.pte. Even we passed TTU_SPLIT_HUGE_PMD, we will trigger a WARN_ON_ONCE due to the page isn't in swapcache. Since UCE is rare in real world, and race with reclaimation is more rare, just skipping the hwpoisoned large folio is enough. memory_failure() will handle it if the UCE is triggered again. This happens when memory reclaim for large folio races with memory_failure(), and will lead to kernel panic. The race is as follows: cpu0 cpu1 shrink_folio_list memory_failure TestSetPageHWPoison unmap_poisoned_folio --> trigger BUG_ON due to unmap_poisoned_folio couldn't handle large folio [tujinjiang@huawei.com: add comment to unmap_poisoned_folio()] Link: https://lkml.kernel.org/r/69fd4e00-1b13-d5f7-1c82-705c7d977ea4@huawei.com Link: https://lkml.kernel.org/r/20250627125747.3094074-2-tujinjiang@huawei.com Signed-off-by: Jinjiang Tu Fixes: 1b0449544c64 ("mm/vmscan: don't try to reclaim hwpoison folio") Reported-by: syzbot+3b220254df55d8ca8a61@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68412d57.050a0220.2461cf.000e.GAE@google.com/ Acked-by: David Hildenbrand Reviewed-by: Miaohe Lin Acked-by: Zi Yan Reviewed-by: Oscar Salvador Cc: Kefeng Wang Cc: Michal Hocko Cc: Oscar Salvador Cc: Signed-off-by: Andrew Morton --- diff --git a/mm/memory-failure.c b/mm/memory-failure.c index b91a33fb6c694..225dddff091d7 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -1561,6 +1561,10 @@ static int get_hwpoison_page(struct page *p, unsigned long flags) return ret; } +/* + * The caller must guarantee the folio isn't large folio, except hugetlb. + * try_to_unmap() can't handle it. + */ int unmap_poisoned_folio(struct folio *folio, unsigned long pfn, bool must_kill) { enum ttu_flags ttu = TTU_IGNORE_MLOCK | TTU_SYNC | TTU_HWPOISON; diff --git a/mm/vmscan.c b/mm/vmscan.c index f8dfd2864bbf4..424412680cfcc 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1138,6 +1138,14 @@ retry: goto keep; if (folio_contain_hwpoisoned_page(folio)) { + /* + * unmap_poisoned_folio() can't handle large + * folio, just skip it. memory_failure() will + * handle it if the UCE is triggered again. + */ + if (folio_test_large(folio)) + goto keep_locked; + unmap_poisoned_folio(folio, folio_pfn(folio), false); folio_unlock(folio); folio_put(folio);