Messages in this thread | | | Date | Wed, 5 Feb 2020 05:29:19 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu |
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On Wed, Feb 05, 2020 at 08:19:21AM -0500, Steven Rostedt wrote: > On Wed, 5 Feb 2020 08:14:09 -0500 > Steven Rostedt <rostedt@goodmis.org> wrote: > > > On Wed, 5 Feb 2020 05:11:10 -0800 > > "Paul E. McKenney" <paulmck@kernel.org> wrote: > > > > > I strongly recommend a comment stating why disabling preemption prevents > > > ftrace_graph_hash from going away. I see the synchronize_rcu() after > > > the rcu_assign_pointer() in ftrace_graph_release(), but I don't see > > > anything that waits on CPUs that RCU is not watching. > > > > > > Of course, event tracing -makes- RCU watch when needed, but if that > > > was set up, then lockdep would not have complained. > > > > > > So what am I missing? > > > > Keep looking in your INBOX and look at the patch I asked you to ack or > > complain about ;-)
Not yet seeing it, but...
> Actually, looking at the code myself, it appears to be missing the > ftrace_sync. Thus, this is a bug, and requires the ftrace sync, as > synchronize_rcu() is not strong enough here. > > Patch in process!
Thank you for chasing it down!
Thanx, Paul
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