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

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Message-ID: <20200205172529.4282a0d1@oasis.local.home>
Date:   Wed, 5 Feb 2020 17:25:29 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.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,  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.

-- Steve