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Wed, 02 Jul 2025 01:27:58 -0700 (PDT) Received: from localhost.localdomain ([118.46.108.16]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-315f54379f7sm18077928a91.34.2025.07.02.01.27.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Jul 2025 01:27:57 -0700 (PDT) From: Jeongjun Park To: dennis@kernel.org, tj@kernel.org, cl@gentwo.org Cc: akpm@linux-foundation.org, vbabka@suse.cz, rientjes@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+e5bd32b79413e86f389e@syzkaller.appspotmail.com, Jeongjun Park Subject: [PATCH] mm/percpu: prevent concurrency problem for pcpu_nr_populated read with spin lock Date: Wed, 2 Jul 2025 17:27:49 +0900 Message-ID: <20250702082749.141616-1-aha310510@gmail.com> X-Mailer: git-send-email 2.47.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 5664C20003 X-Stat-Signature: 9fy5s8casd1fnzk6br6qizf8ryiyg8p4 X-Rspam-User: X-HE-Tag: 1751444879-618080 X-HE-Meta: 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 SS6iEzn9 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 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: Read/Write to pcpu_nr_populated should be performed while protected by pcpu_lock. However, pcpu_nr_pages() reads pcpu_nr_populated without any protection, which causes a data race between read/write. Therefore, when reading pcpu_nr_populated in pcpu_nr_pages(), it should be modified to be protected by pcpu_lock. Reported-by: syzbot+e5bd32b79413e86f389e@syzkaller.appspotmail.com Fixes: 7e8a6304d541 ("/proc/meminfo: add percpu populated pages count") Signed-off-by: Jeongjun Park --- mm/percpu.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/mm/percpu.c b/mm/percpu.c index b35494c8ede2..0f98b857fb36 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -3355,7 +3355,13 @@ void __init setup_per_cpu_areas(void) */ unsigned long pcpu_nr_pages(void) { - return pcpu_nr_populated * pcpu_nr_units; + unsigned long flags, ret; + + spin_lock_irqsave(&pcpu_lock, flags); + ret = pcpu_nr_populated * pcpu_nr_units; + spin_unlock_irqrestore(&pcpu_lock, flags); + + return ret; } /* --