rcu: Keep synchronize_rcu() from enabling irqs in early boot

Making polled RCU grace periods account for expedited grace periods
required acquiring the leaf rcu_node structure's lock during early boot,
but after rcu_init() was called.  This lock is irq-disabled, but the
code incorrectly assumes that irqs are always disabled when invoking
synchronize_rcu().  The exception is early boot before the scheduler has
started, which means that upon return from synchronize_rcu(), irqs will
be incorrectly enabled.

This commit fixes this bug by using irqsave/irqrestore locking primitives.

Fixes: bf95b2bc3e42 ("rcu: Switch polled grace-period APIs to ->gp_seq_polled")

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 6bb8e72..93416af 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1403,30 +1403,32 @@ static void rcu_poll_gp_seq_end(unsigned long *snap)
 // where caller does not hold the root rcu_node structure's lock.
 static void rcu_poll_gp_seq_start_unlocked(unsigned long *snap)
 {
+       unsigned long flags;
        struct rcu_node *rnp = rcu_get_root();
 
        if (rcu_init_invoked()) {
                lockdep_assert_irqs_enabled();
-               raw_spin_lock_irq_rcu_node(rnp);
+               raw_spin_lock_irqsave_rcu_node(rnp, flags);
        }
        rcu_poll_gp_seq_start(snap);
        if (rcu_init_invoked())
-               raw_spin_unlock_irq_rcu_node(rnp);
+               raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 }
 
 // Make the polled API aware of the end of a grace period, but where
 // caller does not hold the root rcu_node structure's lock.
 static void rcu_poll_gp_seq_end_unlocked(unsigned long *snap)
 {
+       unsigned long flags;
        struct rcu_node *rnp = rcu_get_root();
 
        if (rcu_init_invoked()) {
                lockdep_assert_irqs_enabled();
-               raw_spin_lock_irq_rcu_node(rnp);
+               raw_spin_lock_irqsave_rcu_node(rnp, flags);
        }
        rcu_poll_gp_seq_end(snap);
        if (rcu_init_invoked())
-               raw_spin_unlock_irq_rcu_node(rnp);
+               raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 }
 
 /*