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([2a09:bac5:d45b:2e1e::498:19]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ac5f202d78sm4896722a91.3.2026.10.14.08.44.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Oct 2026 08:44:27 -0700 (PDT) From: Nguyen Ngoc Thang To: Breno Leitao Cc: Tejun Heo , Lai Jiangshan , linux-kernel@vger.kernel.org, syzbot+8922e6b8343f70be92e8@syzkaller.appspotmail.com Subject: Re: [PATCH v2] workqueue: annotate the lockless nr_running increment racing with need_more_worker() Date: Wed, 14 Oct 2026 22:44:23 +0700 Message-ID: <20261014154423.20915-1-ngocthang2710.1999@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261013112905.9673-1-ngocthang2710.1999@gmail.com> References: <20261013112905.9673-1-ngocthang2710.1999@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Wed, Oct 14, 2026, Breno Leitao wrote: > Isn't it better to annotate the nr_running field in the structure, rather than > at reading time? Agreed. The lockless increment is how nr_running is meant to work, so the field is the right place for the annotation. v3 marks it __data_racy and drops the data_race() in need_more_worker(): https://lore.kernel.org/all/20261014154342.20661-1-ngocthang2710.1999@gmail.com/ The trade-off is that KCSAN now ignores every access to nr_running, including the locked ones. If someone later adds a decrement without pool->lock, KCSAN won't catch it. I think that's acceptable, because the rules are documented right above the field. Thanks, Nguyen Ngoc Thang