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 712C4243956; Mon, 24 Aug 2026 11:54:24 +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=1787572465; cv=none; b=ZcAlNLRSOz6aNeNUpXcTvv3ic68A0nJZl74e7KJdX9i+8UiTF9wkjiFqi48YaelgWKZCr5XWT0O40CHr79EsDMLUIeM8+ten9Dy8vwiu7qUdwLofkXm80EO4hNOg57cpyt0+6oa5JrNdIMUVkU/0csPnU0NSRBgb34JBNFtD80Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787572465; c=relaxed/simple; bh=Ozze/oJrj+37U2TqYfMqkZIOFqtmeswCzR/2APykZDg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ruO3pTJNewlD3Shu/9Y64E9TNvdtLMxIunzXrDGz5qjcYe2Zl0NgKB9auCTVipBjG+l+NZP+wqMzZFDWYZEOBFVH+VnDCCKYc3cV2a/h9TRkJIjgPQQIFB+57443veT4QIl56AW2ZWqltVMwlrVGhhFlLiNSt3esiv/P8rUjQMs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=giNddQIv; 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="giNddQIv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 176CA1F000E9; Mon, 24 Aug 2026 11:54:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787572464; bh=KArwytZC5OcI2dxvXgYHTkLKrbYoCCTeXuJL++REIfc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=giNddQIvq5n+6Y/ovLVoiMXGw+vC31sbzAXxS+79oI37cKH+MfEG69hBEE6V4CxWP UBeMfIkVtJqowo49ONLGca8U0OWyINxuPDYloHBI7bdklVhNA9/8h9YSR2eDzqHqkA V61c4soGSwjWNndnaZE0mnW/VC/JuFFfCB5iv8CNb9ahuOuEfE+qOjL0TI2q8RSx28 /7zT/XrAjia2djP3xMqO8rChxjaGLNUb+x3xz2Xr/cGE2JdlH1ucQhXqCwRJPXmtyJ h97eMMoSPaA7Wghkd/b+OI3eV9C6tLQjCm5xuhsgo2LDFB3bjQrFgISPnu4mL7V7ea YEQb02/55UeRA== Message-ID: Date: Mon, 24 Aug 2026 13:54:18 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/3] mm: khugepaged: fix swap entry value to folio_pfn() To: Vernon Yang , akpm@linux-foundation.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 References: <20260824092935.73892-1-vernon2gm@gmail.com> <20260824092935.73892-2-vernon2gm@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/24/26 11:29, Vernon Yang wrote: > From: Vernon Yang > > When the swap entries found exceed max_ptes_swap, the loop is left via > break with folio still holding the xarray value that encodes the swap > entry, not valid folio pointer. > > That value is passed to trace_mm_khugepaged_scan_file(), which feeds it > to folio_pfn(). On FLATMEM and SPARSEMEM_VMEMMAP, the page_to_pfn() is > plain pointer arithmetic, so the trace event merely prints bogus > scan_pfn. On classic SPARSEMEM, the page_to_pfn() reads page->flags, > dereferencing the tiny encoded integer and oopsing khugepaged whenever > the trace event is enabled. > > So when folio is the swap entry value, simply set pfn to -1, just like > exhausted scan naturally. > > And the folio_put() has maybe dropped the last reference of folio. The > trace_mm_khugepaged_scan_file() is left with a dangling folio pointer. > so using the folio_pfn() before dropping the reference, closing > use-after-free window. > > Fixes: d41fd2016ed0 ("mm/khugepaged: add tracepoint to hpage_collapse_scan_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 5a48c5406cce..7b526528f85b 100644 > --- a/include/trace/events/huge_memory.h > +++ b/include/trace/events/huge_memory.h > @@ -178,10 +178,10 @@ TRACE_EVENT(mm_collapse_huge_page_swapin, > > TRACE_EVENT(mm_khugepaged_scan_file, > > - TP_PROTO(struct mm_struct *mm, struct folio *folio, struct file *file, > + TP_PROTO(struct mm_struct *mm, unsigned long pfn, struct file *file, > int present, int swap, int result), > > - TP_ARGS(mm, folio, file, present, swap, result), > + TP_ARGS(mm, pfn, file, present, swap, result), > > TP_STRUCT__entry( > __field(struct mm_struct *, mm) > @@ -194,7 +194,7 @@ TRACE_EVENT(mm_khugepaged_scan_file, > > TP_fast_assign( > __entry->mm = mm; > - __entry->pfn = folio ? folio_pfn(folio) : -1; > + __entry->pfn = pfn; > __assign_str(filename); > __entry->present = present; > __entry->swap = swap; > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 79effd3f3da4..00337405c0e0 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2689,6 +2689,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, > int present, swap; > int node = NUMA_NO_NODE; > enum scan_result result = SCAN_SUCCEED; > + unsigned long pfn; > > present = 0; > swap = 0; > @@ -2719,6 +2720,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, > continue; > } > > + pfn = folio_pfn(folio); > if (is_pmd_order(folio_order(folio))) { > result = SCAN_PTE_MAPPED_HUGEPAGE; > /* > @@ -2779,7 +2781,8 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, > } > } > > - trace_mm_khugepaged_scan_file(mm, folio, file, present, swap, result); > + trace_mm_khugepaged_scan_file(mm, (!folio || xa_is_value(folio)) ? -1 : pfn, > + file, present, swap, result); > return result; > } > Shouldn't we just reset PFN to -1 at the beginning of the loop (and set it initially)? -- Cheers, David