Re: [PATCH] rcu: tree_stall: Correctly unlock root node in rcu_check_gp_start_stall

[Paul E. McKenney]

On Sat, Mar 30, 2019 at 09:14:36AM +0530, Neeraj Upadhyay wrote:
> On 3/30/19 2:57 AM, Paul E. McKenney wrote:
> >On Fri, Mar 29, 2019 at 07:52:15PM +0530, Neeraj Upadhyay wrote:
> >>
> >>
> >>On 3/29/19 6:58 PM, Mukesh Ojha wrote:
> >>>
> >>>On 3/29/2019 4:57 PM, Neeraj Upadhyay wrote:
> >>>>Only unlock the root node, if current node (rnp) is not
> >>>>root node.
> >>>>
> >>>>Signed-off-by: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx>
> >>>
> >>>
> >>>
> >>>>---
> >>>>   kernel/rcu/tree_stall.h | 4 +++-
> >>>>   1 file changed, 3 insertions(+), 1 deletion(-)
> >>>>
> >>>>diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> >>>>index f65a73a..0651833 100644
> >>>>--- a/kernel/rcu/tree_stall.h
> >>>>+++ b/kernel/rcu/tree_stall.h
> >>>
> >>>
> >>>why this is showing as under tree_stall.h while it is under
> >>>"kernel/rcu/tree.c"
> >>
> >>It's moved in https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=dev&id=10462d6f58fb6dbde7563e9343505d98d5bfba3d
> >>
> >>Please see linux-rcu dev tree for other changes, which moves code to
> >>this file.
> >>
> >>
> >>Thanks
> >>Neeraj
> >>
> >>>
> >>>>@@ -630,7 +630,9 @@ static void rcu_check_gp_start_stall(struct
> >>>>rcu_node *rnp, struct rcu_data *rdp,
> >>>>           time_before(j, rcu_state.gp_req_activity + gpssdelay) ||
> >>>>           time_before(j, rcu_state.gp_activity + gpssdelay) ||
> >>>>           atomic_xchg(&warned, 1)) {
> >>>>-        raw_spin_unlock_rcu_node(rnp_root); /* irqs remain disabled. */
> >>>>+        if (rnp_root != rnp)
> >>>>+            /* irqs remain disabled. */
> >>>>+            raw_spin_unlock_rcu_node(rnp_root);
> >>>
> >>>Looks good as it will balance the lock .if it is the root_node,
> >>>which was not there earlier, and unlock was happening without any
> >>>lock on root.
> >>>
> >>>Reviewed-by: Mukesh Ojha <mojha@xxxxxxxxxxxxxx>
> >
> >Applied, again thank you both!
> >
> >In both cases, I updated the commit log, so please check to make sure
> >that I didn't mess anything up.
> >
> >							Thanx, Paul
> >
> 
> Thanks Paul. One minor comment on https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=dev&id=ec6530e763046b6bb1f4c2c2aed49ebc68aae2a0
> 
> 
> "it clearly does not make sense to release
> both rnp->lock and rnp->lock"
> 
> should be rnp->lock and rnp_root->lock

Good eyes, fixed, thank you!

							Thanx, Paul

> Thanks
> Neeraj
> 
> >>>Cheers,
> >>>-Mukesh
> >>>
> >>>>           raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> >>>>           return;
> >>>>       }
> >>
> >>-- 
> >>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
>