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Thu, 27 Aug 2026 22:59:52 -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 v4 1/3] mm: khugepaged: fix swap entry value to folio_pfn() Date: Fri, 28 Aug 2026 13:59:24 +0800 Message-ID: <20260828055926.346744-2-vernon2gm@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260828055926.346744-1-vernon2gm@gmail.com> References: <20260828055926.346744-1-vernon2gm@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 0E87740005 X-Stat-Signature: tzzyquamac31gcnrnbj3zpt76bjdberm X-HE-Tag: 1787896793-967921 X-HE-Meta: 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 UKiI3xXr 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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. About calling the respective trace_xxx() functions separately on success and failure, refer to [1]. [1] https://lore.kernel.org/linux-mm/ao6jVbVHLUmuY2UA@gremlin/ 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 | 11 ++++++++++- 2 files changed, 13 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 75639298efc2..b597a3e68606 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2683,6 +2683,7 @@ 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; @@ -2715,6 +2716,7 @@ 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. @@ -2726,6 +2728,7 @@ 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; } @@ -2733,12 +2736,14 @@ 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; } @@ -2771,9 +2776,13 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, } else { result = collapse_file(mm, addr, file, start, cc); } + trace_mm_khugepaged_scan_file(mm, -1, file, present, swap, + SCAN_SUCCEED); + } else { + trace_mm_khugepaged_scan_file(mm, failed_pfn, file, present, + swap, result); } - trace_mm_khugepaged_scan_file(mm, folio, file, present, swap, result); return result; } -- 2.53.0