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Fri, 5 Sep 2025 10:14:55 -0700 (PDT) Date: Fri, 5 Sep 2025 10:14:55 -0700 (PDT) From: "Christoph Lameter (Ampere)" To: Andrew Morton cc: Sebastian Andrzej Siewior , linux-mm@kvack.org, Dennis Zhou , Tejun Heo Subject: Re: [PATCH] mm/percpu: Add a simple double-free check for per-CPU memory In-Reply-To: <20250904155146.485ab7def1b89ed7317b76ad@linux-foundation.org> Message-ID: <7d57bb57-9939-df2e-243a-a0290f79c6f6@gentwo.org> References: <20250904143514.Yk6Ap-jy@linutronix.de> <20250904155146.485ab7def1b89ed7317b76ad@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 5491C40004 X-Rspam-User: X-Stat-Signature: 9mchq769sgh38k4obau3z81fcdh5tsu1 X-Rspamd-Server: rspam09 X-HE-Tag: 1757092496-585973 X-HE-Meta: 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 XASTFj7i 8hBriYU+Q6r09jcV7s+Dv8hVs6MhlRWQIeNhezUqaXm1NqILK8eCDkBj/Y6OtmFKEKqOEmPcMInIH/wR1D7ClCP/7iJnMb8h8eao6zDUKnr8SZXpFqldg069IDjUnJIEcYNO2o2qvX//gZ/w68nDWhjhS5BajqxdXaLR9bGIJJt2N8OCEFD2+qAy+9xF4PfvYCTavnkW/Qx7A/DTeeeXDQYn8DCLCEKZNSsMl6kDPDJ/2pjhaYSTqFTjll43fgyB4iseLWgrRu/v29II= 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, Andrew Morton wrote: > 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! And it could be improved by checking the bit instead of finding the next one.