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b=oclmTG1smnQOpC48pDesd0V2WfcSCWsEfg7LjXlthG0o/N0XZE4Ti1TU6qlPht6Ko F8ywhJEV2w9zd2e8ghxMzXRCfgN5cgcHjOZJ7WoQulxQYIklUtKRod841gFSpUurz7 5mW5xO8rLazBEO9xdSZhCuulWwtGAMfkHcdB2ohs= Date: Thu, 15 Jan 2026 15:13:28 -0800 From: Andrew Morton To: Chris Mason Cc: Dennis Zhou , Tejun Heo , Christoph Lameter , , , "Sebastian Andrzej Siewior" 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) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: ywm583h35pw7616txmh4mgzdgk938edu X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 7ABEF180009 X-HE-Tag: 1768518810-873141 X-HE-Meta: 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 6A4nFNsu /llIVQNexd/mvgpdyD01MUCwV8wi71OsmiquxwALcuix6rH1EBpb7HQ5GBx0CSLBVDplp3LQBL359E/ClvUNf6p2HGp8wPNxWl8dO3sytX8QMBh1pZ3wTE/E6VUT0vVjbhDLGh4UPxVUJOxLLyAkTawwRxyLHa6d/ZPDt2nEPVcHomoeUsuwHJFcYkyryTC/nBaLIBV42APtmMt+O1/BZbym0EaPAXfF91P6kn7UuATYRcfrzlxlVxCuXTBMaEnaT+uvYjjZ0B6NJlJC3phHK/QVCm2YHadfU7lqyP1pcWi6uDCvLx4e8aZR4dQGKK/ZXrYn3wGdsx9Q3HAg= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 14 Jan 2026 04:22:00 -0800 Chris Mason wrote: > On Fri, 19 Dec 2025 16:27:37 -0800 Dennis Zhou 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.