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Tue, 2 Sep 2025 10:39:54 -0700 (PDT) Date: Tue, 2 Sep 2025 10:39:54 -0700 (PDT) From: "Christoph Lameter (Ampere)" To: Vlad Dumitrescu cc: Dennis Zhou , Tejun Heo , Baoquan He , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] percpu: fix race on alloc failed warning limit In-Reply-To: Message-ID: <061405e5-8670-2873-9b6f-0f152863adfc@gentwo.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 83A4A140005 X-Rspam-User: X-Stat-Signature: sgxtd6hwa1r1huic1u85q18ci1dyauu4 X-Rspamd-Server: rspam09 X-HE-Tag: 1756834795-442271 X-HE-Meta: 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 BtdCc0br J8cYWi3hv0tT5ydLBeyFMWQ9uGk6PVCek9wmdh/Z4oUmd4em2okgWd2Dku8+pe0lEa1UCO7ZnDkj1hNWJlsHKvICLoHHAIfPHfmY4spSkNk3pQSrlz3stByOQifJ0Tr3ILolAAxzWDr+jmIiTiJjdR6Jv/rAy2dN60S/n8yxtap7vdUaDdgUg7TU9sHoeflr9ck52m4XvJoZ2A7ytBFrF86XqyXVKo4GJKzA9KfTe3y2ji+LYFrIurn+mGA== 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 Fri, 22 Aug 2025, Vlad Dumitrescu wrote: > + if (do_warn && atomic_read(&warn_limit) > 0) { > + int remaining = atomic_dec_return(&warn_limit); The code creates a race condition since another atomic_dec_return() can happen on another cpu between these two lines. warn_limit can go negative. Use a single atomic operation instead?