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 07108411A17; Mon, 24 Aug 2026 11:59:59 +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=1787572801; cv=none; b=RnTjqv0m7RFGEb1d/kxBP9qv+Vy4S+sQ2nzZ4K3TzmkbpsCcCKfYJgIWXRnZZ+Tu1avk5NROWsNft0SxsDt+zwITVomkJepJXfvDyc5CiTzlG1MGJQTIPKbEtrd7Q3NkgvJY8+A4/O1jxq2E/4lZcvYoZKDGIEgLvHnpuzlzIvU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787572801; c=relaxed/simple; bh=2usbdkss54KNYExpP+scOyPTXsgm7rxDjwMzP29O+S8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fG+YofFMDClskqtHfc5X6S1YZ+XyOBpwAXDcgsxyREjBHGBXQRC5FQ2Q+TCPucrJnze7eu0xbmydWt1C+MYEwwMglt404InazD6C+Ic9Zj1wUhWYN6IoaSt3wBEaOFThcLq82eX0MfDeeYMBV/HsEPpLOYW3eGf0ebP/9I4H1Nk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DV8XUbma; 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="DV8XUbma" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3691D1F000E9; Mon, 24 Aug 2026 11:59:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787572799; bh=rTuYvF3Mu7p31xlyX3il8puWDUAl1lur7TZTZMOinSw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=DV8XUbmaKUGJZhyQ1aHYwN/aGyQChNpP/e/L2YUvyE4Qt2E6lWjS7DsjwkPQCtXPu 11Dgzi+rcPEI2V8DfmdRO+2hM6TZmmOOOCZW+MtGDSp/Iw5jx/tyEPab/lS3768PXt +coJPLqdOA25xoeeLV6zmReX18s1vkXtEyAPQLCTUCl82xr1GdOrVHx073h1aGx3rH IyBrhiIRf77corKNQlykvoVSUJd8TtjLwOLjVZxf4TKijbBl/XOCDUPTu1okWd+VlW NhdOqmSULDHu45jlzUp2eCPONjeTRfoA19bjWYycWlWQp21DAEhUrl4VDPmqbmBmXe zT8NEIkG46Rqg== Message-ID: <8001afe8-84e4-43d4-971b-b23f72070339@kernel.org> Date: Mon, 24 Aug 2026 13:59:53 +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 3/3] mm: khugepaged: fix folio is used after folio_put/unlock() 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> <20260824092935.73892-4-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 > > On the rollback path, folio_put() has already dropped the last reference > of new_folio. On the success path, new_folio is already unlocked and can > be freed concurrently. The trace_mm_khugepaged_collapse_file() is left > with a dangling folio pointer. > > So using the folio_pfn() before dropping the reference, closing > use-after-free window. > > Fixes: 4c9473e87e75 ("mm/khugepaged: add tracepoint to collapse_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 fa828967e1fb..5fb4d92cfd84 100644 > --- a/include/trace/events/huge_memory.h > +++ b/include/trace/events/huge_memory.h > @@ -211,10 +211,10 @@ TRACE_EVENT(mm_khugepaged_scan_file, > ); > > TRACE_EVENT(mm_khugepaged_collapse_file, > - TP_PROTO(struct mm_struct *mm, struct folio *new_folio, pgoff_t index, > + TP_PROTO(struct mm_struct *mm, unsigned long new_pfn, pgoff_t index, > unsigned long addr, bool is_shmem, struct file *file, > int nr, int result), > - TP_ARGS(mm, new_folio, index, addr, is_shmem, file, nr, result), > + TP_ARGS(mm, new_pfn, index, addr, is_shmem, file, nr, result), > TP_STRUCT__entry( > __field(struct mm_struct *, mm) > __field(unsigned long, hpfn) > @@ -228,7 +228,7 @@ TRACE_EVENT(mm_khugepaged_collapse_file, > > TP_fast_assign( > __entry->mm = mm; > - __entry->hpfn = new_folio ? folio_pfn(new_folio) : -1; > + __entry->hpfn = new_pfn; > __entry->index = index; > __entry->addr = addr; > __entry->is_shmem = is_shmem; > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 4e0fca5942dd..24347f1a94ae 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2254,6 +2254,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, > struct address_space *mapping = file->f_mapping; > struct page *dst; > struct folio *folio, *tmp, *new_folio; > + unsigned long new_pfn = -1; > pgoff_t index = 0, end = start + HPAGE_PMD_NR; > LIST_HEAD(pagelist); > XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER); > @@ -2633,6 +2634,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, > retract_page_tables(mapping, start); > if (cc && !cc->is_khugepaged) > result = SCAN_PTE_MAPPED_HUGEPAGE; > + new_pfn = folio_pfn(new_folio); Why not set new_pfn once after successful alloc_charge_folio()? -- Cheers, David