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 170245474E; Mon, 7 Sep 2026 12:26:02 +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=1788783964; cv=none; b=Eq2QtnZQu57Uo/XjXwulWqAR1PJsP9cQySU4QU/Vzhm95k6A8wqr/E+3sDfpptliQoJKh3vFw2ihzLMeybaTFc/ySykxAeVjC3TiWxpvZdlpL+jeWvu85wkajI7IGvaNhg9l95GUkL1+PW0FSvsXWJ8MeL3/F39XO+wbjI3y+Ko= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788783964; c=relaxed/simple; bh=9MTkvOJsI5K4fCtJU8CACmtvC3FZa+nl2Zqmy55d2Z0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=W0CvTRt96T9ufYlH5EwQZPuMCkJKHFs+Cw5IjkcV8iEhmT4db5tswMWwKAhK8JCffWD2PiiCY/tUuptg8oqhvMH7WOm5QSAHpmMzZgV8MbbBE3aKMHh++WGDi9THO/H1ERAVeXyvUGQe9hylDGKlTnVib45jOvT53Mcv8ncLLWw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=M3/tt1xb; 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="M3/tt1xb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 104CB1F00A3D; Mon, 7 Sep 2026 12:25:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788783962; bh=khFAlLB3IE9nHz5wgfKxVmeFcDHKyAwXXbXcSPy92d4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=M3/tt1xbUroc0tnLm8UfmiJG4vFvuRkj3HlzlzSU6Z2rP/ZRKVr0VO/am67MU/DOm 0infuQjOeYcSJ5oDpXmCCveGVc7y90pgw3mAAXAlZ/8PuR71GDXiLnfSVBDwGZEXEK 37VuLhqPawUKwsMgtTI5Tgt3R/Efv7hdyQe70H4x7VOGTwkO/wrtd2pm+7lxWGyqgm tJ2UcP7hiBJala6NQL7RVG6THLmKiGZAsYrf0Gkj0XkoVsKtu/DqS1QSa9C/vILm9r IAs3UC0pgDD+8cHta70g9anwqodk0QnKpCJvjtEvqs3wmcqIiapTSLLBbBBcdKq6Pk FiBqy5ji2Me6w== Message-ID: <53f3afde-b5a7-4c2e-b6b5-8c844d1b6c8e@kernel.org> Date: Mon, 7 Sep 2026 14:25:57 +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 v4 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: <20260828055926.346744-1-vernon2gm@gmail.com> <20260828055926.346744-2-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 8/28/26 07:59, 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. > > About calling the respective trace_xxx() functions separately on success > and failure, refer to [1]. > > [1] https://lore.kernel.org/linux-mm/ao6jVbVHLUmuY2UA@gremlin/ > > 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 | 11 ++++++++++- > 2 files changed, 13 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 75639298efc2..b597a3e68606 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2683,6 +2683,7 @@ 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 failed_pfn = -1; > > present = 0; > swap = 0; > @@ -2715,6 +2716,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, > > if (is_pmd_order(folio_order(folio))) { > result = SCAN_PTE_MAPPED_HUGEPAGE; > + failed_pfn = folio_pfn(folio); > /* > * PMD-sized THP implies that we can only try > * retracting the PTE table. > @@ -2726,6 +2728,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, > node = folio_nid(folio); > if (collapse_scan_abort(node, cc)) { > result = SCAN_SCAN_ABORT; > + failed_pfn = folio_pfn(folio); > folio_put(folio); > break; > } > @@ -2733,12 +2736,14 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, > > if (!folio_test_lru(folio)) { > result = SCAN_PAGE_LRU; > + failed_pfn = folio_pfn(folio); > folio_put(folio); > break; > } > > if (folio_expected_ref_count(folio) + 1 != folio_ref_count(folio)) { > result = SCAN_PAGE_COUNT; > + failed_pfn = folio_pfn(folio); > folio_put(folio); > break; > } > @@ -2771,9 +2776,13 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, > } else { > result = collapse_file(mm, addr, file, start, cc); > } > + trace_mm_khugepaged_scan_file(mm, -1, file, present, swap, > + SCAN_SUCCEED); > + } else { > + trace_mm_khugepaged_scan_file(mm, failed_pfn, file, present, > + swap, result); > } Just curious (maybe Lorenzo suggested that?), why separate out the SCAN_SUCCEED stuff? When result == SCAN_SUCCEED, failed_pfn == -1 no? We set failed_pfn now only when setting result ... Acked-by: David Hildenbrand (Arm) -- Cheers, David