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Fri, 14 Aug 2026 22:20:14 -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 3/3] mm: khugepaged: fix folio is used after folio_put/unlock() Date: Sat, 15 Aug 2026 13:19:24 +0800 Message-ID: <20260815051924.194810-4-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-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BB608120004 X-Stat-Signature: z8cnozjbpx9u51usy1qznswgqiat1cck X-HE-Tag: 1786771215-931495 X-HE-Meta: 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 tb3JZiNx qsvZxKna23Ulc7z2neTCC1czH3YoQCzR7HHwahMs7yzx3J/PBjfsjTqJLNoOBJVmhlTTWhK101sd6LDnnyxmmkOtuva+oDpNSFmxXIoTjFv1sa8n/sKa0uRsQ+dSJJnZzEvqKgDb1VAjcy5946LhA9QNZq3oDkBHHcF7wisd7eAcClbTK2Vd7X+9Ly3yIfxyWdxUr63qheQ7x3IIXp6RCXZ6Mmxbf+XaaLwxUxuHs65CCqdf1TSwj9a5Gh6/gT7rOCQxYoQKAZnCaNaLv51Nz/5rsFFDUoncDoIJ0om92nkRkF8AGbLC9PsP9uwtkxclJcQlwCjjJEeusySe6OcpuELpt2V/0grCkv1PfeDCnHVqdYFHHCM/DjEXrCYpdeK4lGyUQW5XvVCg4If1wPgBQCD++lywuhU3UCiip3LGN3lLPSyiMPUt81ZuoGu6mhtOsGcz4vpAEw13OQ9E= 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 5dc71d292f47..1b301d4e2dba 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 7c8c48577408..7df0fd2d2fdc 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2247,6 +2247,7 @@ 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); @@ -2626,6 +2627,7 @@ 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); /* @@ -2664,12 +2666,13 @@ 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