rcu: Prohibit grace periods during early boot

Greater use of RCU during early boot (before the scheduler is operating)
is causing RCU to attempt to start grace periods during that time, which
in turn is resulting in both RCU and the callback functions attempting
to use the scheduler before it is ready.

This commit prevents these problems by prohibiting RCU grace periods
until after the scheduler has spawned the first non-idle task.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 0051dbf6958eb27b29c0ed95db2e7b7a80cf1ed1..9970116163ba4725342c2484434322ec23ae5c1b 100644 (file)
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -838,8 +838,11 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
        struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
        struct rcu_node *rnp = rcu_get_root(rsp);
 
-       if (!cpu_needs_another_gp(rsp, rdp) || rsp->fqs_active) {
-               if (cpu_needs_another_gp(rsp, rdp))
+       if (!rcu_scheduler_fully_active ||
+           !cpu_needs_another_gp(rsp, rdp) ||
+           rsp->fqs_active) {
+               if (rcu_scheduler_fully_active &&
+                   cpu_needs_another_gp(rsp, rdp))
                        rsp->fqs_need_gp = 1;
                if (rnp->completed == rsp->completed) {
                        raw_spin_unlock_irqrestore(&rnp->lock, flags);