From: Frederic Weisbecker <[email protected]> Offloaded CPUs do not migrate their callbacks, instead relying on their rcuo kthread to invoke them. But if the CPU is offline, it will be running neither its RCU_SOFTIRQ handler nor its rcuc kthread. This means that de-offloading an offline CPU that still has pending callbacks will strand those callbacks. This commit therefore refuses to toggle offline CPUs having pending callbacks.
Cc: Josh Triplett <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: Mathieu Desnoyers <[email protected]> Cc: Lai Jiangshan <[email protected]> Cc: Joel Fernandes <[email protected]> Cc: Neeraj Upadhyay <[email protected]> Cc: Thomas Gleixner <[email protected]> Suggested-by: Paul E. McKenney <[email protected]> Tested-by: Boqun Feng <[email protected]> Signed-off-by: Frederic Weisbecker <[email protected]> Signed-off-by: Paul E. McKenney <[email protected]> --- kernel/rcu/tree_plugin.h | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 1b870d0..b70cc91 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2227,6 +2227,15 @@ static int __rcu_nocb_rdp_deoffload(struct rcu_data *rdp) printk("De-offloading %d\n", rdp->cpu); rcu_nocb_lock_irqsave(rdp, flags); + /* + * If there are still pending work offloaded, the offline + * CPU won't help much handling them. + */ + if (cpu_is_offline(rdp->cpu) && !rcu_segcblist_empty(&rdp->cblist)) { + rcu_nocb_unlock_irqrestore(rdp, flags); + return -EBUSY; + } + rcu_segcblist_offload(cblist, false); if (rdp->nocb_cb_sleep) { -- 2.9.5
