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[34.150.221.228]) by smtp.gmail.com with ESMTPSA id q31-20020a05620a2a5f00b006bb0e5ca4bbsm9479239qkp.85.2022.09.17.09.42.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 17 Sep 2022 09:42:32 -0700 (PDT) From: "Joel Fernandes (Google)" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, rushikesh.s.kadam@intel.com, urezki@gmail.com, neeraj.iitr10@gmail.com, frederic@kernel.org, paulmck@kernel.org, rostedt@goodmis.org, "Joel Fernandes (Google)" Subject: [PATCH rcu/next 1/3] rcu/tree: Use READ_ONCE() for lockless read of rnp->qsmask Date: Sat, 17 Sep 2022 16:41:58 +0000 Message-Id: <20220917164200.511783-2-joel@joelfernandes.org> X-Mailer: git-send-email 2.37.3.968.ga6b4b080e4-goog In-Reply-To: <20220917164200.511783-1-joel@joelfernandes.org> References: <20220917164200.511783-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-0.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS,URIBL_BLACK autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The rnp->qsmask is locklessly accessed from rcutree_dying_cpu(). This may help avoid load tearing due to concurrent access, KCSAN issues, and preserve sanity of people reading the mask in tracing. Reviewed-by: Frederic Weisbecker Signed-off-by: Joel Fernandes (Google) --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 0ca21ac0f064..5ec97e3f7468 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2106,7 +2106,7 @@ int rcutree_dying_cpu(unsigned int cpu) if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) return 0; - blkd = !!(rnp->qsmask & rdp->grpmask); + blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask); trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq), blkd ? TPS("cpuofl-bgp") : TPS("cpuofl")); return 0; -- 2.37.3.968.ga6b4b080e4-goog