From: Steven Rostedt <rostedt@goodmis.org>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: 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>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: Re: [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu
Date: Tue, 4 Feb 2020 20:01:16 -0500 [thread overview]
Message-ID: <20200204200116.479f0c60@oasis.local.home> (raw)
In-Reply-To: <20200203163301.GB85781@google.com>
On Mon, 3 Feb 2020 11:33:01 -0500
Joel Fernandes <joel@joelfernandes.org> wrote:
> > --- a/kernel/trace/trace.h
> > +++ b/kernel/trace/trace.h
> > @@ -950,22 +950,25 @@ extern void __trace_graph_return(struct trace_array *tr,
> > unsigned long flags, int pc);
> >
> > #ifdef CONFIG_DYNAMIC_FTRACE
> > -extern struct ftrace_hash *ftrace_graph_hash;
> > +extern struct ftrace_hash __rcu *ftrace_graph_hash;
> > extern struct ftrace_hash *ftrace_graph_notrace_hash;
> >
> > static inline int ftrace_graph_addr(struct ftrace_graph_ent *trace)
> > {
> > unsigned long addr = trace->func;
> > int ret = 0;
> > + struct ftrace_hash *hash;
> >
> > preempt_disable_notrace();
> >
> > - if (ftrace_hash_empty(ftrace_graph_hash)) {
> > + hash = rcu_dereference_protected(ftrace_graph_hash, !preemptible());
>
> I think you can use rcu_dereference_sched() here? That way no need to pass
> !preemptible.
>
> A preempt-disabled section is an RCU "sched flavor" section. Flavors are
> consolidated in the backend, but in the front end the dereference API still
> do have flavors.
Unfortunately, doing it with rcu_dereference_sched() causes a lockdep
splat :-P. This is because ftrace can execute when rcu is not
"watching" and that will trigger a lockdep error. That means, this
origin patch *is* correct. I'm re-applying this one.
-- Steve
WARNING: multiple messages have this Message-ID (diff)
From: Steven Rostedt <rostedt@goodmis.org>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: "Paul E . McKenney" <paulmck@kernel.org>,
linux-kernel@vger.kernel.org,
Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [Linux-kernel-mentees] [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu
Date: Tue, 4 Feb 2020 20:01:16 -0500 [thread overview]
Message-ID: <20200204200116.479f0c60@oasis.local.home> (raw)
In-Reply-To: <20200203163301.GB85781@google.com>
On Mon, 3 Feb 2020 11:33:01 -0500
Joel Fernandes <joel@joelfernandes.org> wrote:
> > --- a/kernel/trace/trace.h
> > +++ b/kernel/trace/trace.h
> > @@ -950,22 +950,25 @@ extern void __trace_graph_return(struct trace_array *tr,
> > unsigned long flags, int pc);
> >
> > #ifdef CONFIG_DYNAMIC_FTRACE
> > -extern struct ftrace_hash *ftrace_graph_hash;
> > +extern struct ftrace_hash __rcu *ftrace_graph_hash;
> > extern struct ftrace_hash *ftrace_graph_notrace_hash;
> >
> > static inline int ftrace_graph_addr(struct ftrace_graph_ent *trace)
> > {
> > unsigned long addr = trace->func;
> > int ret = 0;
> > + struct ftrace_hash *hash;
> >
> > preempt_disable_notrace();
> >
> > - if (ftrace_hash_empty(ftrace_graph_hash)) {
> > + hash = rcu_dereference_protected(ftrace_graph_hash, !preemptible());
>
> I think you can use rcu_dereference_sched() here? That way no need to pass
> !preemptible.
>
> A preempt-disabled section is an RCU "sched flavor" section. Flavors are
> consolidated in the backend, but in the front end the dereference API still
> do have flavors.
Unfortunately, doing it with rcu_dereference_sched() causes a lockdep
splat :-P. This is because ftrace can execute when rcu is not
"watching" and that will trigger a lockdep error. That means, this
origin patch *is* correct. I'm re-applying this one.
-- Steve
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Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees
next prev parent reply other threads:[~2020-02-05 1:01 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 [this message]
2020-02-05 1:01 ` 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
2020-02-05 13:19 ` [Linux-kernel-mentees] " 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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