linux-kernel - Re: [PATCH] srcu: Fix incorrect condition in srcu_funnel_exp

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Message-Id: <20180214214245.GS3617@linux.vnet.ibm.com>
Date:   Wed, 14 Feb 2018 13:42:45 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Byungchul Park <byungchul.park@....com>
Cc:     jiangshanlai@...il.com, josh@...htriplett.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, linux-kernel@...r.kernel.org,
        kernel-team@....com
Subject: Re: [PATCH] srcu: Fix incorrect condition in srcu_funnel_exp_start()

On Wed, Feb 14, 2018 at 05:59:54PM +0900, Byungchul Park wrote:
> We should've kept sp->srcu_gp_seq_needed_exp the furthest. But
> it probably fails because of the incorrect condition. Fix it.
> 
> Signed-off-by: Byungchul Park <byungchul.park@....com>

Good catch, and thank you for reviewing the SRCU code, but Ildar Ismagilov
beat you to this one.  Please see 574428dee1f3 ("rcu: Fix misprint in
srcu_funnel_exp_start") in -rcu.

							Thanx, Paul

> ---
>  kernel/rcu/srcutree.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index d5cea81..44bc0fa 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -626,7 +626,7 @@ static void srcu_funnel_exp_start(struct srcu_struct *sp, struct srcu_node *snp,
>  		spin_unlock_irqrestore_rcu_node(snp, flags);
>  	}
>  	spin_lock_irqsave_rcu_node(sp, flags);
> -	if (!ULONG_CMP_LT(sp->srcu_gp_seq_needed_exp, s))
> +	if (ULONG_CMP_LT(sp->srcu_gp_seq_needed_exp, s))
>  		sp->srcu_gp_seq_needed_exp = s;
>  	spin_unlock_irqrestore_rcu_node(sp, flags);
>  }
> -- 
> 1.9.1
>