linux-kernel - Re: [PATCH] rcu: Fix up pending cbs check in rcu_prepare_for

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Message-Id: <20170807140939.GV3730@linux.vnet.ibm.com>
Date:   Mon, 7 Aug 2017 07:09:39 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Neeraj Upadhyay <neeraju@...eaurora.org>
Cc:     josh@...htriplett.org, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu: Fix up pending cbs check in rcu_prepare_for_idle

On Mon, Aug 07, 2017 at 07:31:27PM +0530, Neeraj Upadhyay wrote:
> 
> 
> On 08/07/2017 06:10 PM, Paul E. McKenney wrote:
> >On Mon, Aug 07, 2017 at 11:20:10AM +0530, Neeraj Upadhyay wrote:
> >>Pending cbs check in rcu_prepare_for_idle is inversed
> >>in the sense that, it should accelerate if there are
> >>pending cbs; but, the check does the opposite. So,
> >>fix it.
> >>
> >>Fixes: 15fecf89e46a ("srcu: Abstract multi-tail callback list handling")
> >>Signed-off-by: Neeraj Upadhyay <neeraju@...eaurora.org>
> >Good catch!  Queued for review and testing.
> >
> >Just out of curiosity, how did you find this one?
> 
> Hi Paul, found the issue while reading the code.

Very good, and please feel free to continue reading and finding more
bugs!  ;-)

							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 908b309..b8f51df 100644
> >>--- a/kernel/rcu/tree_plugin.h
> >>+++ b/kernel/rcu/tree_plugin.h
> >>@@ -1493,7 +1493,7 @@ static void rcu_prepare_for_idle(void)
> >>  	rdtp->last_accelerate = jiffies;
> >>  	for_each_rcu_flavor(rsp) {
> >>  		rdp = this_cpu_ptr(rsp->rda);
> >>-		if (rcu_segcblist_pend_cbs(&rdp->cblist))
> >>+		if (!rcu_segcblist_pend_cbs(&rdp->cblist))
> >>  			continue;
> >>  		rnp = rdp->mynode;
> >>  		raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
> >>-- 
> >>QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
> >>member of the Code Aurora Forum, hosted by The Linux Foundation
> >>
> 
> -- 
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
> member of the Code Aurora Forum, hosted by The Linux Foundation
>