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[34.150.221.228]) by smtp.gmail.com with ESMTPSA id s16-20020ac85290000000b0034305a91aaesm11060794qtn.83.2022.09.01.15.17.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Sep 2022 15:17:59 -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, vineeth@bitbyteword.org, boqun.feng@gmail.com, "Joel Fernandes (Google)" Subject: [PATCH v5 03/18] rcu/tree: Use READ_ONCE() for lockless read of rnp->qsmask Date: Thu, 1 Sep 2022 22:17:05 +0000 Message-Id: <20220901221720.1105021-4-joel@joelfernandes.org> X-Mailer: git-send-email 2.37.2.789.g6183377224-goog In-Reply-To: <20220901221720.1105021-1-joel@joelfernandes.org> References: <20220901221720.1105021-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-2.1 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,T_SCC_BODY_TEXT_LINE autolearn=ham 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/store tearing due to concurrent access, KCSAN issues, and preserve sanity of people reading the mask in tracing. 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; -- 2.37.2.789.g6183377224-goog