linux-kernel - Re: [PATCH] percpu: add basic double free check

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Message-Id: <20260115151328.38cc7cf0d0b8bf97ee5b3791@linux-foundation.org>
Date: Thu, 15 Jan 2026 15:13:28 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Chris Mason <clm@...a.com>
Cc: Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>, Christoph
 Lameter <cl@...ux.com>, <linux-mm@...ck.org>,
 <linux-kernel@...r.kernel.org>, "Sebastian Andrzej Siewior"
 <bigeasy@...utronix.de>
Subject: Re: [PATCH] percpu: add basic double free check

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

> On Fri, 19 Dec 2025 16:27:37 -0800 Dennis Zhou <dennis@...nel.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.