linux-kernel - Re: [PATCH] rcu/nocb: Fix uninitialized variable in nocb_gp

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Message-ID: <20190923161403.GB7828@paulmck-ThinkPad-P72>
Date:   Mon, 23 Sep 2019 09:14:03 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] rcu/nocb: Fix uninitialized variable in nocb_gp_wait()

On Mon, Sep 23, 2019 at 05:26:34PM +0300, Dan Carpenter wrote:
> We never set this to false.  This probably doesn't affect most people's
> runtime because GCC will automatically initialize it to false at certain
> common optimization levels.  But that behavior is related to a bug in
> GCC and obviously should not be relied on.
> 
> Fixes: 5d6742b37727 ("rcu/nocb: Use rcu_segcblist for no-CBs CPUs")
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

Good catch!  Queued for v5.5, thank you!

							Thanx, Paul

> ---
>  kernel/rcu/tree_plugin.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 2defc7fe74c3..fa08d55f7040 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1946,7 +1946,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
>  	int __maybe_unused cpu = my_rdp->cpu;
>  	unsigned long cur_gp_seq;
>  	unsigned long flags;
> -	bool gotcbs;
> +	bool gotcbs = false;
>  	unsigned long j = jiffies;
>  	bool needwait_gp = false; // This prevents actual uninitialized use.
>  	bool needwake;
> -- 
> 2.20.1
>