On Fri, Nov 13, 2020 at 01:13:32PM +0100, Frederic Weisbecker wrote:
> RCU needs to check if the cpu hotplug lock is held, in the middle of
> other conditions to check the sanity of RCU-nocb. Provide a helper for
> that.
>
> Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
> Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
> Cc: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> ---
> include/linux/cpu.h | 1 +
> kernel/cpu.c | 7 +++++++
> 2 files changed, 8 insertions(+)
>
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index d6428aaf67e7..27eb3875e45a 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -118,6 +118,7 @@ extern void cpus_read_lock(void);
> extern void cpus_read_unlock(void);
> extern int cpus_read_trylock(void);
> extern void lockdep_assert_cpus_held(void);
> +extern int lockdep_is_cpus_held(void);
> extern void cpu_hotplug_disable(void);
> extern void cpu_hotplug_enable(void);
> void clear_tasks_mm_cpumask(int cpu);
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 6ff2578ecf17..3cca5b27de25 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -330,6 +330,13 @@ void lockdep_assert_cpus_held(void)
> percpu_rwsem_assert_held(&cpu_hotplug_lock);
> }
>
> +#ifdef CONFIG_LOCKDEP
> +int lockdep_is_cpus_held(void)
> +{
> + return percpu_rwsem_is_held(&cpu_hotplug_lock);
> +}
> +#endif
> +
> static void lockdep_acquire_cpus_lock(void)
> {
> rwsem_acquire(&cpu_hotplug_lock.dep_map, 0, 0, _THIS_IP_);
This patch may trigger a build error with !CONFIG_HOTPLUG.
Here is a fixed version:
---
>From 80609608b29758e43e8d8d6beaca486b8c42bb43 Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <frederic@xxxxxxxxxx>
Date: Wed, 11 Nov 2020 23:53:13 +0100
Subject: [PATCH] cpu/hotplug: Add lockdep_is_cpus_held()
RCU needs to check if the cpu hotplug lock is held, in the middle of
other conditions to check the sanity of RCU-nocb. Provide a helper for
that.
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
---
include/linux/cpu.h | 2 ++
kernel/cpu.c | 7 +++++++
2 files changed, 9 insertions(+)
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index d6428aaf67e7..3aaa0687e8df 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -111,6 +111,8 @@ static inline void cpu_maps_update_done(void)
#endif /* CONFIG_SMP */
extern struct bus_type cpu_subsys;
+extern int lockdep_is_cpus_held(void);
+
#ifdef CONFIG_HOTPLUG_CPU
extern void cpus_write_lock(void);
extern void cpus_write_unlock(void);
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6ff2578ecf17..3cca5b27de25 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -330,6 +330,13 @@ void lockdep_assert_cpus_held(void)
percpu_rwsem_assert_held(&cpu_hotplug_lock);
}
+#ifdef CONFIG_LOCKDEP
+int lockdep_is_cpus_held(void)
+{
+ return percpu_rwsem_is_held(&cpu_hotplug_lock);
+}
+#endif
+
static void lockdep_acquire_cpus_lock(void)
{
rwsem_acquire(&cpu_hotplug_lock.dep_map, 0, 0, _THIS_IP_);
--
2.25.1
