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

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Message-Id: <20180219010446.GS3617@linux.vnet.ibm.com>
Date:   Sun, 18 Feb 2018 17:04:46 -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 Mon, Feb 19, 2018 at 08:36:30AM +0900, Byungchul Park wrote:
> On 2/15/2018 6:42 AM, Paul E. McKenney wrote:
> >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.
> 
> Hi Paul,
> 
> I'm sorry I'm late. It's been Lunar New Year holiday since last
> thursday.

Not a problem!

> Do you mean:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
> 
> Is this rcu's main dev-tree?

It is indeed!

> Thanks for replying anyway, and happy new year~

And a very happy Lunar New Year to you and yours!!!

							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
> >>
> >
> >
> 
> -- 
> Thanks,
> Byungchul
>