From 226d68fb6c0a22cf8cc258ff8912956516f944c1 Mon Sep 17 00:00:00 2001 From: Neeraj Upadhyay Date: Wed, 18 Aug 2021 13:34:00 +0530 Subject: [PATCH] rcu: Fix existing exp request check in sync_sched_exp_online_cleanup() [ Upstream commit f0b2b2df5423fb369ac762c77900bc7765496d58 ] The sync_sched_exp_online_cleanup() checks to see if RCU needs an expedited quiescent state from the incoming CPU, sending it an IPI if so. Before sending IPI, it checks whether expedited qs need has been already requested for the incoming CPU, by checking rcu_data.cpu_no_qs.b.exp for the current cpu, on which sync_sched_exp_online_cleanup() is running. This works for the case where incoming CPU is same as self. However, for the case where incoming CPU is different from self, expedited request won't get marked, which can potentially delay reporting of expedited quiescent state for the incoming CPU. Fixes: e015a3411220 ("rcu: Avoid self-IPI in sync_sched_exp_online_cleanup()") Signed-off-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney Signed-off-by: Sasha Levin --- kernel/rcu/tree_exp.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 8760b6e..0ffe185 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -759,7 +759,7 @@ static void sync_sched_exp_online_cleanup(int cpu) my_cpu = get_cpu(); /* Quiescent state either not needed or already requested, leave. */ if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) || - __this_cpu_read(rcu_data.cpu_no_qs.b.exp)) { + rdp->cpu_no_qs.b.exp) { put_cpu(); return; } -- 2.7.4