[Linux-kernel-mentees] [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu

Steven Rostedt rostedt at goodmis.org
Wed Feb 5 13:19:21 UTC 2020


On Wed, 5 Feb 2020 08:14:09 -0500
Steven Rostedt <rostedt at goodmis.org> wrote:

> On Wed, 5 Feb 2020 05:11:10 -0800
> "Paul E. McKenney" <paulmck at 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 ;-) 


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!

-- Steve



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