From: "Paul E. McKenney" <paulmck@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Joel Fernandes <joel@joelfernandes.org>,
Amol Grover <frextrite@gmail.com>, Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org,
linux-kernel-mentees@lists.linuxfoundation.org,
Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Subject: Re: [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu
Date: Wed, 5 Feb 2020 05:29:19 -0800 [thread overview]
Message-ID: <20200205132919.GU2935@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20200205081921.34b19d9a@oasis.local.home>
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
next prev parent reply other threads:[~2020-02-05 13:29 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-01 7:27 Amol Grover
2020-02-03 16:33 ` Joel Fernandes
2020-02-04 10:02 ` Steven Rostedt
2020-02-05 1:01 ` Steven Rostedt
2020-02-05 5:26 ` Amol Grover
2020-02-05 13:11 ` Paul E. McKenney
2020-02-05 13:14 ` Steven Rostedt
2020-02-05 13:19 ` Steven Rostedt
2020-02-05 13:29 ` Paul E. McKenney [this message]
2020-02-05 22:06 ` Joel Fernandes
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