linux-kernel - Re: [PATCH] tracing: Annotate ftrace_graph_hash pointer with _

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Message-ID: <20200204050229.70e2cb0e@oasis.local.home>
Date:   Tue, 4 Feb 2020 05:02:29 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     Amol Grover <frextrite@...il.com>, Ingo Molnar <mingo@...hat.com>,
        linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu

On Mon, 3 Feb 2020 11:33:01 -0500
Joel Fernandes <joel@...lfernandes.org> wrote:

> >  	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.

Agreed, Amol, can you send an update?

-- Steve