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Tue, 08 Sep 2026 19:58:36 -0700 (PDT) From: Vernon Yang To: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org Cc: nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, zokeefe@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, Vernon Yang Subject: [PATCH v5 2/3] mm: khugepaged: fix folio is used after pte_unmap_unlock() Date: Wed, 9 Sep 2026 10:58:02 +0800 Message-ID: <20260909025804.3233645-3-vernon2gm@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260909025804.3233645-1-vernon2gm@gmail.com> References: <20260909025804.3233645-1-vernon2gm@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Vernon Yang After the page table lock has dropped, the folio can be freed concurrently. The trace_mm_khugepaged_scan_pmd() is left with a dangling folio pointer. So using the folio_pfn() before dropping the page table lock, closing use-after-free window. And other pre-existing bug, When the `for (i = 0; i < HPAGE_PMD_NR; i++)` iteration to terminate and the folio operation preceding is normal, but pfn will be incorrect. so we really only trace the PFN if it really was problematic. Acked-by: David Hildenbrand (Arm) Acked-by: Lorenzo Stoakes (ARM) Fixes: 7d2eba0557c1 ("mm: add tracepoint for scanning pages") Cc: stable@vger.kernel.org Signed-off-by: Vernon Yang --- include/trace/events/huge_memory.h | 6 +++--- mm/khugepaged.c | 10 +++++++++- 2 files changed, 12 insertions(+), 4 deletions(-) diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h index 7b526528f85b..fa828967e1fb 100644 --- a/include/trace/events/huge_memory.h +++ b/include/trace/events/huge_memory.h @@ -55,10 +55,10 @@ SCAN_STATUS TRACE_EVENT(mm_khugepaged_scan_pmd, - TP_PROTO(struct mm_struct *mm, struct folio *folio, + TP_PROTO(struct mm_struct *mm, unsigned long pfn, int referenced, int none_or_zero, int status, int unmapped), - TP_ARGS(mm, folio, referenced, none_or_zero, status, unmapped), + TP_ARGS(mm, pfn, referenced, none_or_zero, status, unmapped), TP_STRUCT__entry( __field(struct mm_struct *, mm) @@ -71,7 +71,7 @@ TRACE_EVENT(mm_khugepaged_scan_pmd, TP_fast_assign( __entry->mm = mm; - __entry->pfn = folio ? folio_pfn(folio) : -1; + __entry->pfn = pfn; __entry->referenced = referenced; __entry->none_or_zero = none_or_zero; __entry->status = status; diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 6ee0ad13a31f..b352c1330f8e 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1612,6 +1612,7 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, enum scan_result result = SCAN_FAIL; struct page *page = NULL; struct folio *folio = NULL; + unsigned long failed_pfn = -1; unsigned long addr; unsigned long enabled_orders; spinlock_t *ptl; @@ -1706,11 +1707,13 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, if (cc->is_khugepaged && !(vma->vm_flags & VM_DROPPABLE) && folio_test_lazyfree(folio) && !pte_dirty(pteval)) { result = SCAN_PAGE_LAZYFREE; + failed_pfn = folio_pfn(folio); goto out_unmap; } if (!folio_test_anon(folio)) { result = SCAN_PAGE_ANON; + failed_pfn = folio_pfn(folio); goto out_unmap; } @@ -1721,6 +1724,7 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, if (folio_maybe_mapped_shared(folio)) { if (++shared > max_ptes_shared) { result = SCAN_EXCEED_SHARED_PTE; + failed_pfn = folio_pfn(folio); count_collapse_event(HPAGE_PMD_ORDER, THP_SCAN_EXCEED_SHARED_PTE, MTHP_STAT_COLLAPSE_EXCEED_SHARED); goto out_unmap; @@ -1738,15 +1742,18 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, node = folio_nid(folio); if (collapse_scan_abort(node, cc)) { result = SCAN_SCAN_ABORT; + failed_pfn = folio_pfn(folio); goto out_unmap; } cc->node_load[node]++; if (!folio_test_lru(folio)) { result = SCAN_PAGE_LRU; + failed_pfn = folio_pfn(folio); goto out_unmap; } if (folio_test_locked(folio)) { result = SCAN_PAGE_LOCK; + failed_pfn = folio_pfn(folio); goto out_unmap; } @@ -1759,6 +1766,7 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, */ if (folio_expected_ref_count(folio) != folio_ref_count(folio)) { result = SCAN_PAGE_COUNT; + failed_pfn = folio_pfn(folio); goto out_unmap; } @@ -1784,7 +1792,7 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, *lock_dropped = true; } out: - trace_mm_khugepaged_scan_pmd(mm, folio, referenced, + trace_mm_khugepaged_scan_pmd(mm, failed_pfn, referenced, none_or_zero, result, unmapped); return result; } -- 2.53.0