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 ADE0E448D1D; Mon, 17 Aug 2026 16:33:59 +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=1786984441; cv=none; b=a3ax6f+46pqd6Ao7OHR3zs8S21G+4141p0aYn+divEUQWU8E6jMhrfnyh0K9FlpGIJWeh04+S0PmreNCrcsnJB8Ip7GhnIvlO/f0SIK9H4YjrI2y7XJuieA/++/ZEPRY9P/xi3aQA0XdreLMANspak+5o4yEObpi3iDsHZxQ/bY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786984441; c=relaxed/simple; bh=U/eLL9bUNSCvrH9sLn2NYPvhZRCuw7ZtYYwXtyU5EtM=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; b=taRmFJ8U68PgjqHRiyTogOXL2dKjd2JQomVIMHGa8wT2R8vWgMdzNzxfAk1a0RrIIzGWd81KolpD9VOrCckLllDeq/rC8qNmxwVI0PRTOOz80slUYsK8KidKH1/066yIKWMD+jXLQaoCO3Q6yblJqz7xe8jF3fmTbrUbtoNiqNM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PVe0wnP6; 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="PVe0wnP6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E21751F00A3F; Mon, 17 Aug 2026 16:33:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786984439; bh=yArJ3n0LedpZD7yr7DsVqSaiwMdPJtOBt5PMrcip4oQ=; h=Date:From:To:Cc:Subject:In-Reply-To; b=PVe0wnP6NQy5lHXwo+hOArsEWIzrAmBGS3XKY5dRqDHavILmjT/IFQ/1+yyQ4FGRQ 1nBrp2wXxv4EjfOQtWbakN3sN+mu/H5ziCgevGS8fbF+0EZBgufhbLQ/AOOTjg5qnI LX02KkOu+3g8lWLRacPiebN0nOvk407RP/DOAI10GjVFOq7pVEPkjJubmLxwgFfDPs zX18+rwFQ4Kkf5rvbhvksCcaRuwit2MkIBSJTl7/kWBRSvOzKnyQuhl7ZjtI/W8kxi MW/gl+czNGXxExoHdOHIJyUM1/l7R0ZZVHgFF2aMwIrCXXMboOlYGIdy2BkOuezO3O WoEAHc5YgmmAw== Date: Mon, 17 Aug 2026 17:33:40 +0100 From: Lorenzo Stoakes 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: 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: On Mon, Aug 17, 2026 at 05:12:01PM +0100, Lorenzo Stoakes (ARM) wrote: > 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; You already defaulted the value to -1, better as: if (folio) pfn = folio_pfn(folio); > > 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. Disregard, I didn't account for lifetime. > > > none_or_zero, result, unmapped); > > return result; > > } > > -- > > 2.53.0 > > > > -- > Cheers, Lorenzo -- Cheers, Lorenzo