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 ACD2D3803FD; Wed, 26 Aug 2026 08:14:49 +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=1787732090; cv=none; b=aaWJu0C2v9iig5Jb3biWdmVFX7ehQ0bbijdPeX9xvrT610CqxQDHLPqOoSe0qTEUkp1nYIl+aVOymqrwAdimbS2ML9IJpFK2KsPzNuhPWdXzWM6+Qqrggl0e6DyWyq7d7l7Q1n9b+9pGc6S+iupB2OMj0WACu4wPMylOcElxcEA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787732090; c=relaxed/simple; bh=g33bWaj+icLi9FHW/7qnA2uuVP49ga3CsQEc9g2FN0A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=B4ex4DMc3YFquyZjAAFynRJMdyiOONLHVPsCMa/0YhDaZQCC1V5LAAdatqY2c7IJNBY2ciqUtYIvtDjqdIyfsboZY21fQKCtkA9zViu1XXCgmswApJGtUmHNatakqiMlax4I470mV78yS1oVRVhfxr/wFCLuWqK8j8b6aA7Gfgo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gEYJJikc; 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="gEYJJikc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E93B41F000E9; Wed, 26 Aug 2026 08:14:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787732089; bh=jc5AoHf2qjE/ikpZjUfB6MnpSBqN1XX0+Zdh1Ro7A4Q=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=gEYJJikc/toz6F8QKezBvlpwgGyWhfluynnS9RhLMjWauJkS61XhCi+K2Vksr8hAV irfSunCZqgGbBgSs3Lr4I9Vx4ardA9nx+pgb/fvWT8ke8hiyZMWU5p6RbSdkPdF/s5 5r6PFfy+CNJkElRqe7mjpXcC3hsI4zVazezxxglECtveJO3aHcdabWELJOx2wdPg5t bDwSj9vqu0VLWeX3bi7PpWuHrZ05rviaJfkuLBMJNcM8H0M02WFb3aYsbSdSnz1ldz F0k63wUZilpSrU1WVU2TKTsPH5KZT66qQ/Mf0W8bRI/RRHU4dNuimyIj8M3m2pi7Zm B9Up3WLdg0eyw== Message-ID: <77412338-b54c-455b-84da-1f39db641c90@kernel.org> Date: Wed, 26 Aug 2026 10:14:43 +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: "Lorenzo Stoakes (ARM)" , Vernon Yang Cc: akpm@linux-foundation.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, 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 8/26/26 10:09, Lorenzo Stoakes (ARM) wrote: > On Mon, Aug 24, 2026 at 05:29:35PM +0800, 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; > > Nitty but: > > Could we use pfn_t? I don't love that we are inconsistent with that. Note that the monstrosity we called pfn_t no longer exits. :) -- Cheers, David