From: Neeraj Upadhyay neeraju@codeaurora.org
[ 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 neeraju@codeaurora.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 2796084ef85a5..454b516ea566e 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -760,7 +760,7 @@ 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; }