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[185.121.47.193]) by smtp.gmail.com with ESMTPSA id t18-20020a2e9d12000000b002e29c50c4dcsm1335473lji.27.2024.05.07.02.35.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 May 2024 02:35:57 -0700 (PDT) From: "Uladzislau Rezki (Sony)" To: "Paul E . McKenney" Cc: RCU , Neeraj upadhyay , Boqun Feng , Hillf Danton , Joel Fernandes , LKML , Uladzislau Rezki , Oleksiy Avramchenko , Frederic Weisbecker Subject: [PATCH 26/48] rcu: Mark loads from rcu_state.n_online_cpus Date: Tue, 7 May 2024 11:35:08 +0200 Message-Id: <20240507093530.3043-27-urezki@gmail.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20240507093530.3043-1-urezki@gmail.com> References: <20240507093530.3043-1-urezki@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: quoted-printable Content-Type: text/plain; charset="utf-8" From: "Paul E. McKenney" The rcu_state.n_online_cpus value is only ever updated by CPU-hotplug operations, which are serialized. However, this value is read locklessly. This commit therefore marks those reads. While in the area, it also adds ASSERT_EXCLUSIVE_WRITER() calls just in case parallel CPU hotplug becomes a thing. Signed-off-by: Paul E. McKenney Signed-off-by: Uladzislau Rezki (Sony) --- kernel/rcu/tree.c | 4 +++- kernel/rcu/tree_stall.h | 6 ++++-- 2 files changed, 7 insertions(+), 3 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 559f2d0d271f..7149b2d5cdd6 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4328,7 +4328,7 @@ EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online); // whether spinlocks may be acquired safely. static bool rcu_init_invoked(void) { - return !!rcu_state.n_online_cpus; + return !!READ_ONCE(rcu_state.n_online_cpus); } =20 /* @@ -4538,6 +4538,7 @@ int rcutree_prepare_cpu(unsigned int cpu) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); rcu_spawn_rnp_kthreads(rnp); rcu_spawn_cpu_nocb_kthread(cpu); + ASSERT_EXCLUSIVE_WRITER(rcu_state.n_online_cpus); WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus + 1); =20 return 0; @@ -4806,6 +4807,7 @@ void rcutree_migrate_callbacks(int cpu) */ int rcutree_dead_cpu(unsigned int cpu) { + ASSERT_EXCLUSIVE_WRITER(rcu_state.n_online_cpus); WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1); // Stop-machine done, so allow nohz_full to disable tick. tick_dep_clear(TICK_DEP_BIT_RCU); diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 62b2c4858028..8a2edf6a1ef5 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -628,7 +628,8 @@ static void print_other_cpu_stall(unsigned long gp_seq,= unsigned long gps) totqlen +=3D rcu_get_n_cbs_cpu(cpu); pr_err("\t(detected by %d, t=3D%ld jiffies, g=3D%ld, q=3D%lu ncpus=3D%d)\= n", smp_processor_id(), (long)(jiffies - gps), - (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_onl= ine_cpus); + (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, + data_race(rcu_state.n_online_cpus)); // Diagnostic read if (ndetected) { rcu_dump_cpu_stacks(); =20 @@ -689,7 +690,8 @@ static void print_cpu_stall(unsigned long gps) totqlen +=3D rcu_get_n_cbs_cpu(cpu); pr_err("\t(t=3D%lu jiffies g=3D%ld q=3D%lu ncpus=3D%d)\n", jiffies - gps, - (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_online_cp= us); + (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, + data_race(rcu_state.n_online_cpus)); // Diagnostic read =20 rcu_check_gp_kthread_expired_fqs_timer(); rcu_check_gp_kthread_starvation(); --=20 2.39.2