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

Paul E. McKenney
2017-08-07T14:11:47Z

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
>