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Fri, 14 Aug 2026 22:20:08 -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, Vernon Yang , stable@vger.kernel.org Subject: [PATCH v2 2/3] mm: khugepaged: fix folio is used after pte_unmap_unlock() Date: Sat, 15 Aug 2026 13:19:23 +0800 Message-ID: <20260815051924.194810-3-vernon2gm@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260815051924.194810-1-vernon2gm@gmail.com> References: <20260815051924.194810-1-vernon2gm@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: 39rw5immjrjmzqd9dnt167k55bm59bh3 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 5075E40006 X-HE-Tag: 1786771210-610062 X-HE-Meta: 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 /YlzdWEZ NRQD7bwmvfX6rfTEGQwugJxxqd+DItn+dc/rujLmE2y25LsvBBlWcIwnwL6/A3urWTdgnm0SuVyvwtFQAMM9366co32TcX4vEA4MNCFZuBNxbjV3df9N5Wro2+UePM+HEQfX7qvzvvUIYwhUjUmZ+s0LME+Xr31N77+2L3kS+1s6QZh3ROm9lwKsEfjyQWQFERK+2O4lV3LLaAPVh3jH1+wTY8fK8vzbd8ACyi4S5G1M/mz5Y6UbHNtdX4sN7dkOI7r8dxr1xD7x97qt+vqVniH+CagipdsIW0j43r9Vf2bSg+Lh5rnIlOUcfm3pyStpigN3W5SUt9TmYv1VYwhyYohyqELufK/T3HjJJSx1gQOZxm29c3OkO/o8RTq5EEac76wWiX3AoPADJwnXUg8D2D9sP28xF0oLDZaPa6mN/0Brf6xJHD9yoH9DI2DRaQY1AFXc/NzKkyK9zRdo= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. 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 | 4 +++- 2 files changed, 6 insertions(+), 4 deletions(-) diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h index d3572d4ef453..5dc71d292f47 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 e7830761d3a2..7c8c48577408 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1603,6 +1603,7 @@ 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 pfn = -1; unsigned long addr; unsigned long enabled_orders; spinlock_t *ptl; @@ -1778,6 +1779,7 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, result = SCAN_SUCCEED; } out_unmap: + pfn = folio ? folio_pfn(folio) : -1; pte_unmap_unlock(pte, ptl); if (result == SCAN_SUCCEED) { /* collapse_huge_page expects the lock to be dropped before calling */ @@ -1788,7 +1790,7 @@ 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, pfn, referenced, none_or_zero, result, unmapped); return result; } -- 2.53.0