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Subject[PATCH tip/core/rcu 22/22] rcu: Prevent offline CPUs from executing RCU core code
From: "Paul E. McKenney" <>

Earlier versions of RCU invoked the RCU core from the CPU_DYING notifier
in order to note a quiescent state for the outgoing CPU. Because the
CPU is marked "offline" during the execution of the CPU_DYING notifiers,
the RCU core had to tolerate being invoked from an offline CPU. However,
commit b1420f1c (Make rcu_barrier() less disruptive) left only tracing
code in the CPU_DYING notifier, so the RCU core need no longer execute
on offline CPUs. This commit therefore enforces this restriction.

Signed-off-by: Paul E. McKenney <>
Signed-off-by: Paul E. McKenney <>
kernel/rcutree.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index d21c2d3..cbf4d05 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1880,6 +1880,8 @@ static void rcu_process_callbacks(struct softirq_action *unused)
struct rcu_state *rsp;

+ if (cpu_is_offline(smp_processor_id()))
+ return;
trace_rcu_utilization("Start RCU core");

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