From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201])
	(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 A4C8D27AC5C
	for <linux-kernel@vger.kernel.org>; Thu, 15 Jan 2026 23:13:29 +0000 (UTC)
Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201
ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116;
	t=1768518809; cv=none; b=D8Ec1iKmDHTt+qcTN5NypFcB/5zgzLh0NHlHOT1e40Jtp2zUnXBSx7MxGhfIjRpFN+q8+uZ5uPA4dZbgBBHU5qrctY6ALZkzLz5OdahPMcmSJS4MJ9trQcuVwyhk5wrRWeEpysewjVIpzNg0JyerLmvMyMaw03/LfG3h7xYOQQI=
ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org;
	s=arc-20240116; t=1768518809; c=relaxed/simple;
	bh=BP+gqIGsJl3UZ8x7v9WfP/7xksK/zyzL1fiY4gW7DRU=;
	h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References:
	 Mime-Version:Content-Type; b=QsO7un4bB+ctgODjwNm4KxIEio2bWZx4F/+eY6eI6bh5e7JK2Tk1Gfn9GLrAsvwdkkJMuIVD8PF0O/z6aADzZcC7O9fF1iaAWFQcDuXW11q7nl/oO2rZ0GfWQVAMPnw+aAnqEUeVZVY1oVXktMpXE3aPDJ2bdokdsndMpNYDCN0=
ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=oclmTG1s; arc=none smtp.client-ip=10.30.226.201
Authentication-Results: smtp.subspace.kernel.org;
	dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="oclmTG1s"
Received: by smtp.kernel.org (Postfix) with ESMTPSA id 16472C116D0;
	Thu, 15 Jan 2026 23:13:29 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org;
	s=korg; t=1768518809;
	bh=BP+gqIGsJl3UZ8x7v9WfP/7xksK/zyzL1fiY4gW7DRU=;
	h=Date:From:To:Cc:Subject:In-Reply-To:References:From;
	b=oclmTG1smnQOpC48pDesd0V2WfcSCWsEfg7LjXlthG0o/N0XZE4Ti1TU6qlPht6Ko
	 F8ywhJEV2w9zd2e8ghxMzXRCfgN5cgcHjOZJ7WoQulxQYIklUtKRod841gFSpUurz7
	 5mW5xO8rLazBEO9xdSZhCuulWwtGAMfkHcdB2ohs=
Date: Thu, 15 Jan 2026 15:13:28 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Chris Mason <clm@meta.com>
Cc: Dennis Zhou <dennis@kernel.org>, Tejun Heo <tj@kernel.org>, Christoph
 Lameter <cl@linux.com>, <linux-mm@kvack.org>,
 <linux-kernel@vger.kernel.org>, "Sebastian Andrzej Siewior"
 <bigeasy@linutronix.de>
Subject: Re: [PATCH] percpu: add basic double free check
Message-Id: <20260115151328.38cc7cf0d0b8bf97ee5b3791@linux-foundation.org>
In-Reply-To: <20260114122209.1075584-1-clm@meta.com>
References: <20251220002737.84100-1-dennis@kernel.org>
	<20260114122209.1075584-1-clm@meta.com>
X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu)
Precedence: bulk
X-Mailing-List: linux-kernel@vger.kernel.org
List-Id: <linux-kernel.vger.kernel.org>
List-Subscribe: <mailto:linux-kernel+subscribe@vger.kernel.org>
List-Unsubscribe: <mailto:linux-kernel+unsubscribe@vger.kernel.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit

On Wed, 14 Jan 2026 04:22:00 -0800 Chris Mason <clm@meta.com> wrote:

> On Fri, 19 Dec 2025 16:27:37 -0800 Dennis Zhou <dennis@kernel.org> wrote:
> 
> > This adds a basic double free check by validating the first bit of the
> > allocation in alloc_map and bound_map are set. If the alloc_map bit is
> > not set, then this means the area is currently unallocated. If the
> > bound_map bit is not set, then we are not freeing from the beginning of
> > the allocation.
> 
> Hi Dennis,
> 
> I ran mm-new through the AI review prompts, and this one was flagged:

So good.

> If nr_alloc is underreported due to this bug, the buffer may be undersized
> for the actual number of allocations tracked in alloc_map, which
> chunk_map_stats() iterates based on the actual bitmap contents.

That's pretty serious, although unlikely to occur.  I'll drop this
version of the patch, thanks.