On 2018-07-09 15:01:54 [-0400], Steven Rostedt wrote: > > which is the trace_cgroup_rmdir() trace event in cgroup_rmdir(). The > > trace event invokes cgroup_path() which acquires a spin_lock_t and this > > is invoked within a preempt_disable()ed section. > > Correct. And I wish no trace event took spin locks. is there an easy way to detect this? I mean instead hitting the trace event with debug enabled and doing a review of each of them. > > It says "Preemption disabled at" migrate_enable() but this is not true. > > A printk() just before the lock reports preempt_count() of two and > > sometimes one. I *think* > > - one is from rcu_read_lock_sched_notrace() in __DO_TRACE() > > - the second is from preempt_disable_notrace() in ring_buffer_lock_reserve() > > > > I would prefer not to turn kernfs_rename_lock into raw_spin_lock_t. We > > had a similar problem with a i915 trace event which eventually vanished > > (and before I just disabled it). > > > > So how likely are chances that we can use rcu_read_lock() in __DO_TRACE()? > > Not very. Is there a reason for this? I don't think this is documented. I changed it to the "normal" RCU read section and it appeared to work :) > > And how likely are chances that the preempt_disable() in > > ring_buffer_lock_reserve() could be avoided while the trace event is > > invoked? > > Even less likely. The design of the ring buffer is based on not being > able to be preempted. I was expecting this. > > I guess nothing of this is easy peasy. Any suggestions? > > > > One solution, albeit not so pretty, is to move the grabbing of the > path, outside the trace event. But this should work. okay, wasn't aware of the trace_cgroup_##type##_enabled() magic. Yes, this should work. Do you mind posting this upstream? > -- Steve Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
