Re: [PATCH 17/19] cpu/hotplug: Add lockdep_is_cpus_held()

[Frederic Weisbecker]

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:

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