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Message-Id: <20231013115902.1059735-15-frederic@kernel.org>
Date: Fri, 13 Oct 2023 13:58:58 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
Boqun Feng <boqun.feng@...il.com>,
Joel Fernandes <joel@...lfernandes.org>,
Josh Triplett <josh@...htriplett.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Neeraj Upadhyay <neeraj.upadhyay@....com>,
"Paul E . McKenney" <paulmck@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Uladzislau Rezki <urezki@...il.com>, rcu <rcu@...r.kernel.org>
Subject: [PATCH 14/18] rcu: Conditionally build CPU-hotplug teardown callbacks
Among the three CPU-hotplug teardown RCU callbacks, two of them early
exit if CONFIG_HOTPLUG_CPU=n, and one is left unchanged. In any case
all of them have an implementation when CONFIG_HOTPLUG_CPU=n.
Align instead with the common way to deal with CPU-hotplug teardown
callbacks and provide a proper stub when they are not supported.
Reviewed-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
include/linux/rcutree.h | 11 +++-
kernel/rcu/tree.c | 114 +++++++++++++++++++---------------------
2 files changed, 63 insertions(+), 62 deletions(-)
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 153cfc7bbffd..46875c4e9f56 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -110,9 +110,16 @@ void rcu_all_qs(void);
/* RCUtree hotplug events */
int rcutree_prepare_cpu(unsigned int cpu);
int rcutree_online_cpu(unsigned int cpu);
-int rcutree_offline_cpu(unsigned int cpu);
+void rcu_cpu_starting(unsigned int cpu);
+
+#ifdef CONFIG_HOTPLUG_CPU
int rcutree_dead_cpu(unsigned int cpu);
int rcutree_dying_cpu(unsigned int cpu);
-void rcu_cpu_starting(unsigned int cpu);
+int rcutree_offline_cpu(unsigned int cpu);
+#else
+#define rcutree_dead_cpu NULL
+#define rcutree_dying_cpu NULL
+#define rcutree_offline_cpu NULL
+#endif
#endif /* __LINUX_RCUTREE_H */
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 2e1e7eadf2cc..f9c6b2680cbb 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4237,25 +4237,6 @@ static bool rcu_init_invoked(void)
return !!rcu_state.n_online_cpus;
}
-/*
- * Near the end of the offline process. Trace the fact that this CPU
- * is going offline.
- */
-int rcutree_dying_cpu(unsigned int cpu)
-{
- bool blkd;
- struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
- struct rcu_node *rnp = rdp->mynode;
-
- if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
- return 0;
-
- 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;
-}
-
/*
* All CPUs for the specified rcu_node structure have gone offline,
* and all tasks that were preempted within an RCU read-side critical
@@ -4301,23 +4282,6 @@ static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
}
}
-/*
- * The CPU has been completely removed, and some other CPU is reporting
- * this fact from process context. Do the remainder of the cleanup.
- * There can only be one CPU hotplug operation at a time, so no need for
- * explicit locking.
- */
-int rcutree_dead_cpu(unsigned int cpu)
-{
- if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
- return 0;
-
- 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);
- return 0;
-}
-
/*
* Propagate ->qsinitmask bits up the rcu_node tree to account for the
* first CPU in a given leaf rcu_node structure coming online. The caller
@@ -4470,29 +4434,6 @@ int rcutree_online_cpu(unsigned int cpu)
return 0;
}
-/*
- * Near the beginning of the process. The CPU is still very much alive
- * with pretty much all services enabled.
- */
-int rcutree_offline_cpu(unsigned int cpu)
-{
- unsigned long flags;
- struct rcu_data *rdp;
- struct rcu_node *rnp;
-
- rdp = per_cpu_ptr(&rcu_data, cpu);
- rnp = rdp->mynode;
- raw_spin_lock_irqsave_rcu_node(rnp, flags);
- rnp->ffmask &= ~rdp->grpmask;
- raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-
- rcutree_affinity_setting(cpu, cpu);
-
- // nohz_full CPUs need the tick for stop-machine to work quickly
- tick_dep_set(TICK_DEP_BIT_RCU);
- return 0;
-}
-
/*
* Mark the specified CPU as being online so that subsequent grace periods
* (both expedited and normal) will wait on it. Note that this means that
@@ -4646,7 +4587,60 @@ void rcutree_migrate_callbacks(int cpu)
cpu, rcu_segcblist_n_cbs(&rdp->cblist),
rcu_segcblist_first_cb(&rdp->cblist));
}
-#endif
+
+/*
+ * The CPU has been completely removed, and some other CPU is reporting
+ * this fact from process context. Do the remainder of the cleanup.
+ * There can only be one CPU hotplug operation at a time, so no need for
+ * explicit locking.
+ */
+int rcutree_dead_cpu(unsigned int cpu)
+{
+ 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);
+ return 0;
+}
+
+/*
+ * Near the end of the offline process. Trace the fact that this CPU
+ * is going offline.
+ */
+int rcutree_dying_cpu(unsigned int cpu)
+{
+ bool blkd;
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+ struct rcu_node *rnp = rdp->mynode;
+
+ 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;
+}
+
+/*
+ * Near the beginning of the process. The CPU is still very much alive
+ * with pretty much all services enabled.
+ */
+int rcutree_offline_cpu(unsigned int cpu)
+{
+ unsigned long flags;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+
+ rdp = per_cpu_ptr(&rcu_data, cpu);
+ rnp = rdp->mynode;
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ rnp->ffmask &= ~rdp->grpmask;
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
+ rcutree_affinity_setting(cpu, cpu);
+
+ // nohz_full CPUs need the tick for stop-machine to work quickly
+ tick_dep_set(TICK_DEP_BIT_RCU);
+ return 0;
+}
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/*
* On non-huge systems, use expedited RCU grace periods to make suspend
--
2.34.1
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