linux-kernel - Re: [PATCH] kernel/trace: Use rcu_assign_pointer() for setting fgraph hash pointers

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Message-ID: <20200205223415.GA55522@google.com>
Date:   Wed, 5 Feb 2020 17:34:15 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        paulmck@...nel.org, frextrite@...il.com, rcu@...r.kernel.org,
        madhuparnabhowmik04@...il.com
Subject: Re: [PATCH] kernel/trace: Use rcu_assign_pointer() for setting
 fgraph hash pointers

On Wed, Feb 05, 2020 at 05:25:29PM -0500, Steven Rostedt wrote:
> On Wed,  5 Feb 2020 17:18:08 -0500
> "Joel Fernandes (Google)" <joel@...lfernandes.org> wrote:
> 
> > set_ftrace_early_graph() sets pointers without any explicit
> > release-barriers. Let us use rcu_assign_pointer() to ensure the same.
> > 
> > Note that ftrace_early_graph() calls ftrace_graph_set_hash() which does
> > do mutex_unlock(&ftrace_lock); which should imply a release barrier.
> > However it is better to not depend on it and just use
> > rcu_assign_pointer() which should also avoid sparse errors in the
> > future.
> 
> This is going to have to wait for the next merge window, as I'm already
> *very* late, and I've pushed the limit to what I will add at this time
> frame.

I understand, no problem. I will resend it next merge window.

thanks,

 - Joel

> 
> -- Steve
>