rcu: Remove local_irq_disable() in rcu_preempt_note_context_switch()
The rcu_preempt_note_context_switch() function is on a scheduling fast
path, so it would be good to avoid disabling irqs. The reason that irqs
are disabled is to synchronize process-level and irq-handler access to
the task_struct ->rcu_read_unlock_special bitmask. This commit therefore
makes ->rcu_read_unlock_special instead be a union of bools with a short
allowing single-access checks in RCU's __rcu_read_unlock(). This results
in the process-level and irq-handler accesses being simple loads and
stores, so that irqs need no longer be disabled. This commit therefore
removes the irq disabling from rcu_preempt_note_context_switch().
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ec8b347..42888d7 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1212,6 +1212,13 @@
struct hrtimer dl_timer;
};
+union rcu_special {
+ struct {
+ bool blocked;
+ bool need_qs;
+ } b;
+ short s;
+};
struct rcu_node;
enum perf_event_task_context {
@@ -1264,7 +1271,7 @@
#ifdef CONFIG_PREEMPT_RCU
int rcu_read_lock_nesting;
- char rcu_read_unlock_special;
+ union rcu_special rcu_read_unlock_special;
struct list_head rcu_node_entry;
#endif /* #ifdef CONFIG_PREEMPT_RCU */
#ifdef CONFIG_TREE_PREEMPT_RCU
@@ -2005,16 +2012,11 @@
extern void task_clear_jobctl_pending(struct task_struct *task,
unsigned int mask);
-#ifdef CONFIG_PREEMPT_RCU
-#define RCU_READ_UNLOCK_BLOCKED (1 << 0) /* blocked while in RCU read-side. */
-#define RCU_READ_UNLOCK_NEED_QS (1 << 1) /* RCU core needs CPU response. */
-#endif /* #ifdef CONFIG_PREEMPT_RCU */
-
static inline void rcu_copy_process(struct task_struct *p)
{
#ifdef CONFIG_PREEMPT_RCU
p->rcu_read_lock_nesting = 0;
- p->rcu_read_unlock_special = 0;
+ p->rcu_read_unlock_special.s = 0;
p->rcu_blocked_node = NULL;
INIT_LIST_HEAD(&p->rcu_node_entry);
#endif /* #ifdef CONFIG_PREEMPT_RCU */