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 7530B3ACA65; Tue, 11 Aug 2026 15:19:45 +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=1786461587; cv=none; b=JYmMyQmkJtHvdt7UlyIcKwEowcMALl2y7Aklp/lT18O9oloWUDGYtvJHWdkLZcilkdVAwJaTnWd0Grldcs6Sxnpq5AHuEVsecoujMHOBmR/fPJFJdd2z0o9PZtIEbe+GtdQISc4FrAEk3CEMwAAOzMX3Fu279S1g989rUA8fPoo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786461587; c=relaxed/simple; bh=zKY50OCssChfN+ET3K9i0I7IAfFLBliETzl9BlmewAU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BznsZ0IM6j2TqavGWf6YqwwsqEbDtPUOzu4OrNTlARrRGHX5/VAb+o/UR7vKwhhYq/o918dtar27au9Ocu9DFNChLIWL+dCBSTBWlm+Seab3R0divlDcZGtNY969+bhI+Vy9mbsz2x6RPvMyy882NiEXehG8arPo4T5f7LwFf+w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VkxC/iQ8; 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="VkxC/iQ8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AE01F1F000E9; Tue, 11 Aug 2026 15:19:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786461585; bh=N3sGQ6wm+Gzp0+w751keBcCQghKUsRRShVvsLPMj604=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=VkxC/iQ8k0nyQb/L5x3wdHKisvzuGV2yY8sotHC8igD1DcT6WEz5renkViAmXn2Xg +/QKmxippHxBntGL0+j3FJQQVgkLl1hSx67XjpldKHIm7Av9W5YU3dvj6VREG0uIzz V+GQM15vcEmSoTq79U1vbmVOHw7sZdxNG7JbW0cOEJSZEw9HbVvom6cvwmNM1u7/xd esc3I3q4Z4JE0Ew0HGmGG3QKv7T+tzftD8p4rQTu3QsV2jIcJ7l6eaJZEA3QM8z50N RI2xMB5NNiHQe5MRnMTI8N0x9ji0IUk/M2nSvNcfMSoHWEcZb7qi02/+W6pBWhwRd+ BYHnqqOLGgg3w== Message-ID: <57248ac2-2d5e-4995-9ecd-b71b233fe5d4@kernel.org> Date: Tue, 11 Aug 2026 17:19:38 +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] mm: khugepaged: don't pass swap entry value to trace_mm_khugepaged_scan_file() 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, Vernon Yang , stable@vger.kernel.org References: <20260811133655.267739-1-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 8/11/26 15:36, 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 set folio to NULL before breaking out, the tracepoint maps NULL to > scan_pfn of -1, just like exhausted scan naturally. > > Fixes: d41fd2016ed0 ("mm/khugepaged: add tracepoint to hpage_collapse_scan_file()") > Cc: stable@vger.kernel.org > Signed-off-by: Vernon Yang > --- > mm/khugepaged.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 617bca76db49..bc0d04c9162d 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2696,6 +2696,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, > if (xa_is_value(folio)) { > swap += 1 << xas_get_order(&xas); > if (swap > max_ptes_swap) { > + folio = NULL; > result = SCAN_EXCEED_SWAP_PTE; > count_vm_event(THP_SCAN_EXCEED_SWAP_PTE); > break; Yes, we'll do a folio_pfn(), and used to do a page_to_pfn(). Using the folio after dropping the reference is rather nasty. Instead of passing the folio, should we just pass the pfn directly? -- Cheers, David