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Tue, 08 Sep 2026 19:58:40 -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 3/3] mm: khugepaged: fix folio is used after folio_put/unlock() Date: Wed, 9 Sep 2026 10:58:03 +0800 Message-ID: <20260909025804.3233645-4-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 On the rollback path, folio_put() has already dropped the last reference of new_folio. On the success path, new_folio is already unlocked and can be freed concurrently. The trace_mm_khugepaged_collapse_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) Acked-by: Lorenzo Stoakes (ARM) Fixes: 4c9473e87e75 ("mm/khugepaged: add tracepoint to collapse_file()") 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 fa828967e1fb..5fb4d92cfd84 100644 --- a/include/trace/events/huge_memory.h +++ b/include/trace/events/huge_memory.h @@ -211,10 +211,10 @@ TRACE_EVENT(mm_khugepaged_scan_file, ); TRACE_EVENT(mm_khugepaged_collapse_file, - TP_PROTO(struct mm_struct *mm, struct folio *new_folio, pgoff_t index, + TP_PROTO(struct mm_struct *mm, unsigned long new_pfn, pgoff_t index, unsigned long addr, bool is_shmem, struct file *file, int nr, int result), - TP_ARGS(mm, new_folio, index, addr, is_shmem, file, nr, result), + TP_ARGS(mm, new_pfn, index, addr, is_shmem, file, nr, result), TP_STRUCT__entry( __field(struct mm_struct *, mm) __field(unsigned long, hpfn) @@ -228,7 +228,7 @@ TRACE_EVENT(mm_khugepaged_collapse_file, TP_fast_assign( __entry->mm = mm; - __entry->hpfn = new_folio ? folio_pfn(new_folio) : -1; + __entry->hpfn = new_pfn; __entry->index = index; __entry->addr = addr; __entry->is_shmem = is_shmem; diff --git a/mm/khugepaged.c b/mm/khugepaged.c index b352c1330f8e..e13d233b9967 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2260,6 +2260,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, struct address_space *mapping = file->f_mapping; struct page *dst; struct folio *folio, *tmp, *new_folio; + unsigned long new_pfn = -1; pgoff_t index = 0, end = start + HPAGE_PMD_NR; LIST_HEAD(pagelist); XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER); @@ -2279,6 +2280,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, result = alloc_charge_folio(&new_folio, mm, cc, HPAGE_PMD_ORDER); if (result != SCAN_SUCCEED) goto out; + new_pfn = folio_pfn(new_folio); mapping_set_update(&xas, mapping); @@ -2682,7 +2684,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, folio_put(new_folio); out: VM_BUG_ON(!list_empty(&pagelist)); - trace_mm_khugepaged_collapse_file(mm, new_folio, index, addr, is_shmem, file, HPAGE_PMD_NR, result); + trace_mm_khugepaged_collapse_file(mm, new_pfn, index, addr, is_shmem, file, HPAGE_PMD_NR, result); return result; } -- 2.53.0