linux-kernel - Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings

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Date:	Fri, 31 Aug 2012 11:24:29 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall
 warnings

On Thu, Aug 30, 2012 at 11:56:24AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mckenney@...aro.org>
> 
> If a given CPU avoids the idle loop but also avoids starting a new
> RCU grace period for a full minute, RCU can issue spurious RCU CPU
> stall warnings.  This commit fixes this issue by adding a check for
> ongoing grace period to avoid these spurious stall warnings.
> 
> Reported-by: Becky Bruce <bgillbruce@...il.com>
> Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

Reviewed-by: Josh Triplett <josh@...htriplett.org>

> ---
>  kernel/rcutree.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index fbe43b0..e58097b 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -820,7 +820,8 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
>  	j = ACCESS_ONCE(jiffies);
>  	js = ACCESS_ONCE(rsp->jiffies_stall);
>  	rnp = rdp->mynode;
> -	if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) {
> +	if (rcu_gp_in_progress(rsp) &&
> +	    (ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) {
>  
>  		/* We haven't checked in, so go dump stack. */
>  		print_cpu_stall(rsp);
> -- 
> 1.7.8
> 
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