Re: [PATCH] rcu: Fix up pending cbs check in rcu_prepare_for_idle

From	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] rcu: Fix up pending cbs check in rcu_prepare_for_idle
Date	2017-08-07 16:20 +0200
Message-ID	<ubR2X-W5-47@gated-at.bofh.it> (permalink)
References	<ubJf4-4dI-13@gated-at.bofh.it> <ubPDR-8gK-31@gated-at.bofh.it> <ubQTg-Rb-3@gated-at.bofh.it>
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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@codeaurora.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
>

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[PATCH] rcu: Fix up pending cbs check in rcu_prepare_for_idle Neeraj Upadhyay <neeraju@codeaurora.org> - 2017-08-07 08:00 +0200
  Re: [PATCH] rcu: Fix up pending cbs check in rcu_prepare_for_idle "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-07 14:50 +0200
    Re: [PATCH] rcu: Fix up pending cbs check in rcu_prepare_for_idle Neeraj Upadhyay <neeraju@codeaurora.org> - 2017-08-07 16:10 +0200
      Re: [PATCH] rcu: Fix up pending cbs check in rcu_prepare_for_idle "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-07 16:20 +0200

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