From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D1569449B2D; Mon, 17 Aug 2026 16:12:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786983137; cv=none; b=sx3pGc4mXQCcK4dyeqyoYU5UUv75ZhA05nFy2NCNurWHQWLFNSnFGEmE173aJD6fBOpIM2dGHwHtQ+8G+frdrIF2eHdoZTBNsScEkak1MzVDenvhzQZKMs+F8frOc828QMIYBlt+vqeU2i+HqTbMLepGhF/cBJUKPlOyv66lxBk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786983137; c=relaxed/simple; bh=QoSuaU8OFRJme2lV0npACZeRyv+Id01q+oSFvvjDlVk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QnJhCRELlWjHhW8Pw9AxfzIzX9b+p8VVMkDPH+twXuoB8W709w8O+DKkvV2V+/WWBc3eXfpiLT09wk0DBT9w9PzRgT7AEh8rgcxDjDeQaSoSAJR0pezb4VmS+FtgL+JhCVcfeZAMLeChcsHsbOCQbraHD3x5dwhyFxRFZINsMMk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CMzJBZll; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="CMzJBZll" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 07ABF1F000E9; Mon, 17 Aug 2026 16:12:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786983135; bh=FQUvrkehKpwo8jNXcs2xc61eh0IJJnnFxqJq+fJqvow=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=CMzJBZllxMo1S2XbnPp2+ODTD9IPmNxlpBKWEemO/6ae+sZK+yiC8J1YN2t5oLDQI zykM+NdAwk/Gm2M1oBQqTlZDJMXMHTRDHj8Eix49bl/yj9DHUNwS3f7wNDtKiacYNz lfbYgrzB4XALIVHOZs2SSzfwSvmKM1ZgLGzaa5BbjmON4PrTADLdblHH1KacPLVnpU 5Pq/alv6hVTGv6eIQdLLz4bJ/wDVsNvLNmXbOY4w6JP1V4f1zli5fkXFI3p1Vndej4 494gx6ntrO8yURjrgPHQsPXVJBl7IVRIcWUlYL40rjIDDc3YMkmAWuCCV7Zxn6K9qn Icya7Qcq03yvw== Date: Mon, 17 Aug 2026 17:11:56 +0100 From: "Lorenzo Stoakes (ARM)" To: Vernon Yang Cc: akpm@linux-foundation.org, david@kernel.org, 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: Re: [PATCH v2 2/3] mm: khugepaged: fix folio is used after pte_unmap_unlock() Message-ID: References: <20260815051924.194810-1-vernon2gm@gmail.com> <20260815051924.194810-3-vernon2gm@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260815051924.194810-3-vernon2gm@gmail.com> On Sat, Aug 15, 2026 at 01:19:23PM +0800, Vernon Yang wrote: > 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, Same comment as 1/3 I don't see why we should be storing a pfn value used nowhere else just for tracing. > none_or_zero, result, unmapped); > return result; > } > -- > 2.53.0 > -- Cheers, Lorenzo