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Tue, 08 Sep 2026 19:58:32 -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 1/3] mm: khugepaged: fix swap entry value to folio_pfn() Date: Wed, 9 Sep 2026 10:58:01 +0800 Message-ID: <20260909025804.3233645-2-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> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam04 X-Rspam-User: X-Stat-Signature: y5ad54zcf41fj8a7yxu5rrca1e3wgx9b X-Rspamd-Queue-Id: 9913140006 X-HE-Tag: 1788922714-939907 X-HE-Meta: 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 CjtW3abQ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Vernon Yang When the swap entries found exceed max_ptes_swap, the loop is left via break with folio still holding the xarray value that encodes the swap entry, not valid folio pointer. That value is passed to trace_mm_khugepaged_scan_file(), which feeds it to folio_pfn(). On FLATMEM and SPARSEMEM_VMEMMAP, the page_to_pfn() is plain pointer arithmetic, so the trace event merely prints bogus scan_pfn. On classic SPARSEMEM, the page_to_pfn() reads page->flags, dereferencing the tiny encoded integer and oopsing khugepaged whenever the trace event is enabled. So when folio is the swap entry value, simply set pfn to -1, just like exhausted scan naturally. And the folio_put() has maybe dropped the last reference of folio. The trace_mm_khugepaged_scan_file() is left with a dangling folio pointer. so using the folio_pfn() before dropping the reference, closing use-after-free window. Acked-by: David Hildenbrand (Arm) Fixes: d41fd2016ed0 ("mm/khugepaged: add tracepoint to hpage_collapse_scan_file()") Cc: stable@vger.kernel.org Signed-off-by: Vernon Yang --- include/trace/events/huge_memory.h | 6 +++--- mm/khugepaged.c | 7 ++++++- 2 files changed, 9 insertions(+), 4 deletions(-) diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h index 5a48c5406cce..7b526528f85b 100644 --- a/include/trace/events/huge_memory.h +++ b/include/trace/events/huge_memory.h @@ -178,10 +178,10 @@ TRACE_EVENT(mm_collapse_huge_page_swapin, TRACE_EVENT(mm_khugepaged_scan_file, - TP_PROTO(struct mm_struct *mm, struct folio *folio, struct file *file, + TP_PROTO(struct mm_struct *mm, unsigned long pfn, struct file *file, int present, int swap, int result), - TP_ARGS(mm, folio, file, present, swap, result), + TP_ARGS(mm, pfn, file, present, swap, result), TP_STRUCT__entry( __field(struct mm_struct *, mm) @@ -194,7 +194,7 @@ TRACE_EVENT(mm_khugepaged_scan_file, TP_fast_assign( __entry->mm = mm; - __entry->pfn = folio ? folio_pfn(folio) : -1; + __entry->pfn = pfn; __assign_str(filename); __entry->present = present; __entry->swap = swap; diff --git a/mm/khugepaged.c b/mm/khugepaged.c index e6947fe142ee..6ee0ad13a31f 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2690,6 +2690,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, int present, swap; int node = NUMA_NO_NODE; enum scan_result result = SCAN_SUCCEED; + unsigned long failed_pfn = -1; present = 0; swap = 0; @@ -2722,6 +2723,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, if (is_pmd_order(folio_order(folio))) { result = SCAN_PTE_MAPPED_HUGEPAGE; + failed_pfn = folio_pfn(folio); /* * PMD-sized THP implies that we can only try * retracting the PTE table. @@ -2733,6 +2735,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, node = folio_nid(folio); if (collapse_scan_abort(node, cc)) { result = SCAN_SCAN_ABORT; + failed_pfn = folio_pfn(folio); folio_put(folio); break; } @@ -2740,12 +2743,14 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, if (!folio_test_lru(folio)) { result = SCAN_PAGE_LRU; + failed_pfn = folio_pfn(folio); folio_put(folio); break; } if (folio_expected_ref_count(folio) + 1 != folio_ref_count(folio)) { result = SCAN_PAGE_COUNT; + failed_pfn = folio_pfn(folio); folio_put(folio); break; } @@ -2780,7 +2785,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, } } - trace_mm_khugepaged_scan_file(mm, folio, file, present, swap, result); + trace_mm_khugepaged_scan_file(mm, failed_pfn, file, present, swap, result); return result; } -- 2.53.0