From: Steven Rostedt <rostedt@goodmis.org>
To: "Paul E. McKenney" <paulmck@kernel.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 08:19:21 -0500 [thread overview]
Message-ID: <20200205081921.34b19d9a@oasis.local.home> (raw)
In-Reply-To: <20200205081409.4550aa67@oasis.local.home>
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 ;-)
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
WARNING: multiple messages have this Message-ID (diff)
From: Steven Rostedt <rostedt@goodmis.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: linux-kernel@vger.kernel.org,
Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
Ingo Molnar <mingo@redhat.com>,
Joel Fernandes <joel@joelfernandes.org>,
linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [Linux-kernel-mentees] [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu
Date: Wed, 5 Feb 2020 08:19:21 -0500 [thread overview]
Message-ID: <20200205081921.34b19d9a@oasis.local.home> (raw)
In-Reply-To: <20200205081409.4550aa67@oasis.local.home>
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 ;-)
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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Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees
next prev parent reply other threads:[~2020-02-05 13:19 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-01 7:27 [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu Amol Grover
2020-02-01 7:27 ` [Linux-kernel-mentees] " Amol Grover
2020-02-03 16:33 ` Joel Fernandes
2020-02-03 16:33 ` [Linux-kernel-mentees] " Joel Fernandes
2020-02-04 10:02 ` Steven Rostedt
2020-02-04 10:02 ` [Linux-kernel-mentees] " Steven Rostedt
2020-02-05 1:01 ` Steven Rostedt
2020-02-05 1:01 ` [Linux-kernel-mentees] " Steven Rostedt
2020-02-05 5:26 ` Amol Grover
2020-02-05 5:26 ` [Linux-kernel-mentees] " Amol Grover
2020-02-05 13:11 ` Paul E. McKenney
2020-02-05 13:11 ` [Linux-kernel-mentees] " Paul E. McKenney
2020-02-05 13:14 ` Steven Rostedt
2020-02-05 13:14 ` [Linux-kernel-mentees] " Steven Rostedt
2020-02-05 13:19 ` Steven Rostedt [this message]
2020-02-05 13:19 ` Steven Rostedt
2020-02-05 13:29 ` Paul E. McKenney
2020-02-05 13:29 ` [Linux-kernel-mentees] " Paul E. McKenney
2020-02-05 22:06 ` Joel Fernandes
2020-02-05 22:06 ` [Linux-kernel-mentees] " Joel Fernandes
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