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Mon, 24 Aug 2026 02:30:15 -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 v3 3/3] mm: khugepaged: fix folio is used after folio_put/unlock() Date: Mon, 24 Aug 2026 17:29:35 +0800 Message-ID: <20260824092935.73892-4-vernon2gm@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260824092935.73892-1-vernon2gm@gmail.com> References: <20260824092935.73892-1-vernon2gm@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0E8C84000B X-Stat-Signature: fzc78s6rg7na1b18rddt1za9ihjry8ga X-HE-Tag: 1787563816-362277 X-HE-Meta: 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 p9cy2sQ2 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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 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. 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 | 5 ++++- 2 files changed, 7 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 4e0fca5942dd..24347f1a94ae 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2254,6 +2254,7 @@ 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); @@ -2633,6 +2634,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, retract_page_tables(mapping, start); if (cc && !cc->is_khugepaged) result = SCAN_PTE_MAPPED_HUGEPAGE; + new_pfn = folio_pfn(new_folio); folio_unlock(new_folio); /* @@ -2671,12 +2673,13 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, } new_folio->mapping = NULL; + new_pfn = folio_pfn(new_folio); folio_unlock(new_folio); 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