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

[Mukesh Ojha]

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 <neer...@codeaurora.org>



---
  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"

@@ -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 <mo...@codeaurora.org>

Cheers,
-Mukesh

                raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
                return;
        }