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b=KAptc5/ow0L8NZ/HhSobu/rOexgQf5jdu6+4K2GUnvKtK13PJCOIOiMgKsgvPNJxm qD3hM99Dt7XvDO3oX5Gn8zuXHPkS6i68ADKoU8mrq94J7u6wXd780pJMvo2V4HfaHR LVmWOYkF9rxAyGavOlcTMCodISo6Tsvy770RmT9o= Date: Thu, 4 Sep 2025 15:51:46 -0700 From: Andrew Morton To: Sebastian Andrzej Siewior Cc: linux-mm@kvack.org, Dennis Zhou , Tejun Heo , Christoph Lameter Subject: Re: [PATCH] mm/percpu: Add a simple double-free check for per-CPU memory Message-Id: <20250904155146.485ab7def1b89ed7317b76ad@linux-foundation.org> In-Reply-To: <20250904143514.Yk6Ap-jy@linutronix.de> References: <20250904143514.Yk6Ap-jy@linutronix.de> 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-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 5C364100002 X-Stat-Signature: qwperb3dnumf753beztawoupndgwohi4 X-Rspam-User: X-HE-Tag: 1757026308-171154 X-HE-Meta: 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 3Gyyq3F8 CFSDge/NeBOzGISkLSuiOIJ7qusxil4M1o0X1lTAlUTXlwOHfeGcwCaZ24LRQs6SQcm9UWsNiFERYI/dSLsAEH17HB80WrKv+LFrua7CIipY1EpNKwXIQ/vccFmIjPBIDqwwBWJt+HjACdw2a40zM050ka+GtETly06Yn88gcoQJmCPMUxMDMRBbkM0B0xPQr3th+dpgZQNJz8AkRbQVk/UHBnPH7060bWgbEjB01HM03D8JqYndkLOhaGtYqpt2lr9fsXD/Te01U5YNikS8s4ZFXwA== 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 Thu, 4 Sep 2025 16:35:14 +0200 Sebastian Andrzej Siewior wrote: > The free path clears the allocation bits in pcpu_chunk::alloc_map. A > simple double free check would be to check if the bits, which are about > to be cleared, are already cleared. > Nice idea. It's hardly a fast path!