From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f173.google.com (mail-pl1-f173.google.com [209.85.214.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 51D2B279DC2 for ; Fri, 21 Aug 2026 08:19:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787300368; cv=none; b=dY34f45Oo/ucIo6K+LaXe4e7WKhLFE+MUj9I4AAJ8HB875uhopJuvhqi09xhrZSCW5fX9PwX+GLF4tIZxL+DtwX8wKIdOYe0USQCkdHdCSMm/9k1/v8K+vPOglTOJMdrIvn5hgs0YxXdqcUnTPG/fYHUEd9eUrzicnLIBtppDIQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787300368; c=relaxed/simple; bh=7IYOKQHnRf+eUCm70nBAatamYiIz53y0hAqBgYLgpPU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Sqf0PVypkEAy6fzLcufff0fdrRkJULuqJyB1Z6pfPpFdPF/vIr6vGEoIoKYtTE8DZ08i9G+FcLdmBNGLP5iSv0s97MDEkGnr7nzrD7FngLBS+5x8+pFKHAio08cIHMVWUqku+9RBTT9PeehWxAc1H5t6JSFxB68ow6JRXIDGTsI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=mPIIL+IO; arc=none smtp.client-ip=209.85.214.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="mPIIL+IO" Received: by mail-pl1-f173.google.com with SMTP id d9443c01a7336-2cc891373e0so8888165ad.2 for ; Fri, 21 Aug 2026 01:19:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1787300367; x=1787905167; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=lhXuBcyJmXYpDqWCX/Ojyplzefto48/xHEW5jp//TXY=; b=mPIIL+IOnFBCoZaNNwAqg0hbOyO5RbY0LDJZXxvQENf5dh81OGr5o8F2/dUYkpx1Jy caNiKLZJyJUuVsuI8WtbbHLf0V1xLH27KBae4enbspiWZjQE2CufSDMghfna7JbYV82X y5GBBC//9BeD9MUTdZo6VU8nhhp6YKQE6WPMQMLfSqBHi9xFyIWIPK6S7PHjmNQRYJSw FjHXa1cCLqm+w+sOcaWVNLjE0NdGj8rRgWGxRa8udMfDVrPYz7h3qRsfV6NyiGgo3g7E iLrvfz77Lpq17rGngDSaoUPDtrbIe8sO4sEMJYN1FCMjWXiM3O3w7OdbmBOcZ3JOqhNU hHag== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787300367; x=1787905167; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=lhXuBcyJmXYpDqWCX/Ojyplzefto48/xHEW5jp//TXY=; b=HvjnEd68035CPfFsJz6Nxl1eDseRjpIRGCczfvMhlw3qo10B0pp+sPYQ6IX/CMIows KraET1zPxklRHXFHXiwk3PXHbFYDPhhXUXRp5Em5wv0XH9WBWiBmRbVNw+r/JFupugRW LlrhNA+WL1FhG6xFuJTekeanH7nXYquySIDw2ECbbV5/NvHP+O68R55MH1pUHX0DCf5a W0IHL/gXG6bLddc//QnQLQknLtWXWg1qaaTOq812oDD+qVDb47tkEysfLH+mM+Q0j9uz NrCimJQcLDCA/z0WRFvAUb4s7PRB0SpPKI07SgzF/dmSzQ4u2pXl7lbGd+Y4XJUmGarO 08Dw== X-Forwarded-Encrypted: i=1; AHgh+Rrs8FHtMqrwt5gIO9cyHYvgoHRMBJTH1WbatfmeF5doQ3eDIOkLyjvW81AVqeZ5mPG3HQqSZVYPKN1qwac=@vger.kernel.org X-Gm-Message-State: AFuF++mSZh5wJ1ioJIHjW9BYWBkbHV3n30yEfe0RxzBAHpa5RSPv6bvS /Js/tSqi+oInbvbUWsg0OhQ87M6E8e8lKqdx1ggPwjOA7gqX1X7dxysL X-Gm-Gg: AR+sD12CUSzLoxQUFXcq5oJPDfQa1GNcXjmbhsesW7xXJxXzC3CkJZMVOGPDZ+NdvPi ZUGgZRe0+FGxoHbhTjdpxwZ2J54u/xH/7ZOYLqISQ7/DE3Voq/cnokXM+3/i1iNUiw/vcduuU+a ZYo6NegkOp2ok/kC2xNHcN6TsYyrpz7z+MNGwBTFBChQMR7Z3Q9y+fKYGEps07mWjwxZZ1BPkEJ csSM9qF8grrCrZ1axXLdecM8ZRF1wmT7aRRuQprQcYnnzKcfsJEShugnaXYilJMzyx4LHf8B1ey GcnfNZIS59AUA1mVF/auANaGT2+zNxNjmwr9oy5XhYaaySOVj8f2d2IYuxuPVIjF8OhcUrJSsh+ Z3E5UXBIide18tRu7ra8FZYn1a4fkSgdgtXsMJmZRKDAr0X5QqM8W1IIDddlBNTzZ2oNF6Stl5A Lz6wcbJi5F9DzAdYsxzjgSfTpxlFV74XD7yiu3H5JWBoL8IA4DrhJwcWWRa5t6FMUgOmY3UluGX c4= X-Received: by 2002:a17:903:354b:b0:2c0:a555:80d6 with SMTP id d9443c01a7336-2d64ade4a69mr92013265ad.2.1787300366663; Fri, 21 Aug 2026 01:19:26 -0700 (PDT) Received: from localhost.localdomain ([240e:b8f:1df9:a600:c693:b19f:ada0:748]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2d62e36e15fsm16222015ad.45.2026.08.21.01.19.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 Aug 2026 01:19:26 -0700 (PDT) Date: Fri, 21 Aug 2026 16:19:18 +0800 From: Vernon Yang To: Lorenzo Stoakes 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: <10f5d327-d86b-4971-9344-ce29f40f8955@gmail.com> References: 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 05:33:40PM +0100, Lorenzo Stoakes wrote: > 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); > LGTM, Thanks! -- Cheers, Vernon