On Fri, May 12, 2017 at 01:15:46PM -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rost...@goodmis.org>
>
> Allow get_online_cpus() to be recursive. If a lock is taken while under
> "get_online_cpus()", it can call get_online_cpus() as well, just as long as
> it is never held without being under get_online_cpus(), but then calling it.
>
> GOC() -> Lock(X) -> GOC()
>
> is OK, as long as
>
> Lock(X) -> GOC()
>
> does not exist.
>
> Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
Does ->goc_depth also need to be initialized in include/linux/init_task.h?
It seems like C-language initialization-to-zero would cover this,
but there is a lot of initialization to zero values in init_task.h
(including but not limited to some RCU stuff).
Other than that, this does look like it might ease use of get_online_cpus()
in combination with CPU-hotplug notifiers, although it would not have
made any difference in any of the RCU use cases.
Thanx, Paul
> ---
> include/linux/sched.h | 1 +
> kernel/cpu.c | 9 +++++++++
> kernel/fork.c | 1 +
> 3 files changed, 11 insertions(+)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 993e7e25a3a5..8f272ab57685 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -813,6 +813,7 @@ struct task_struct {
> unsigned int lockdep_recursion;
> struct held_lock held_locks[MAX_LOCK_DEPTH];
> gfp_t lockdep_reclaim_gfp;
> + int goc_depth;
> #endif
>
> #ifdef CONFIG_UBSAN
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 983163ef36ee..0dbdf1e69715 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -209,12 +209,21 @@ DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);
>
> void get_online_cpus(void)
> {
> +#ifdef CONFIG_LOCKDEP
> + if (current->goc_depth++)
> + return;
> +#endif
> percpu_down_read(&cpu_hotplug_lock);
> }
> EXPORT_SYMBOL_GPL(get_online_cpus);
>
> void put_online_cpus(void)
> {
> +#ifdef CONFIG_LOCKDEP
> + WARN_ON_ONCE(current->goc_depth < 1);
> + if (--current->goc_depth)
> + return;
> +#endif
> percpu_up_read(&cpu_hotplug_lock);
> }
> EXPORT_SYMBOL_GPL(put_online_cpus);
> diff --git a/kernel/fork.c b/kernel/fork.c
> index dd5a371c392a..8aedcd011ccc 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1658,6 +1658,7 @@ static __latent_entropy struct task_struct
> *copy_process(
> p->lockdep_depth = 0; /* no locks held yet */
> p->curr_chain_key = 0;
> p->lockdep_recursion = 0;
> + p->goc_depth = 0;
> #endif
>
> #ifdef CONFIG_DEBUG_MUTEXES
> --
> 2.10.2
>
>
