Messages in this thread | | | Date | Fri, 12 May 2017 11:35:59 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [RFC][PATCH 2/5] cpu-hotplug: Allow get_online_cpus() to nest |
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On Fri, May 12, 2017 at 01:15:46PM -0400, Steven Rostedt wrote: > From: "Steven Rostedt (VMware)" <rostedt@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) <rostedt@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 > >
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