[RFC][PATCH] rcu: Clean up TASKS_RCU() abuse

[Peter Zijlstra <peterz@infradead.org>]

Hi

I recently ran into TASKS_RCU() and wondered why we can't use normal
coding patterns to do the same.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 include/linux/rcupdate.h | 33 +++++++++++++++++++++++++++++++--
 kernel/exit.c            |  9 +++------
 2 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index a0189ba67fde..15a82372b372 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -389,7 +389,7 @@ static inline void rcu_init_nohz(void)
  * macro rather than an inline function to avoid #include hell.
  */
 #ifdef CONFIG_TASKS_RCU
-#define TASKS_RCU(x) x
+
 extern struct srcu_struct tasks_rcu_exit_srcu;
 #define rcu_note_voluntary_context_switch(t) \
 	do { \
@@ -397,9 +397,38 @@ extern struct srcu_struct tasks_rcu_exit_srcu;
 		if (READ_ONCE((t)->rcu_tasks_holdout)) \
 			WRITE_ONCE((t)->rcu_tasks_holdout, false); \
 	} while (0)
+
+static inline int tasks_rcu_read_lock(void)
+{
+	int idx;
+
+	preempt_disable();
+	idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
+	preempt_enable();
+
+	return idx;
+}
+
+static inline void tasks_rcu_read_unlock(int idx)
+{
+	preempt_disable();
+	__srcu_read_unlock(&tasks_rcu_exit_srcu, idx);
+	preempt_enable();
+}
+
 #else /* #ifdef CONFIG_TASKS_RCU */
-#define TASKS_RCU(x) do { } while (0)
+
 #define rcu_note_voluntary_context_switch(t)	rcu_all_qs()
+
+static inline int tasks_rcu_read_lock(void)
+{
+	return 0;
+}
+
+static inline void tasks_rcu_read_unlock(int idx)
+{
+}
+
 #endif /* #else #ifdef CONFIG_TASKS_RCU */
 
 /**
diff --git a/kernel/exit.c b/kernel/exit.c
index 07110c6020a0..cd5644baeb22 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -653,8 +653,7 @@ static inline void check_stack_usage(void) {}
 void do_exit(long code)
 {
 	struct task_struct *tsk = current;
-	int group_dead;
-	TASKS_RCU(int tasks_rcu_i);
+	int group_dead, tasks_rcu_i;
 
 	profile_task_exit(tsk);
 
@@ -763,9 +762,7 @@ void do_exit(long code)
 	 */
 	flush_ptrace_hw_breakpoint(tsk);
 
-	TASKS_RCU(preempt_disable());
-	TASKS_RCU(tasks_rcu_i = __srcu_read_lock(&tasks_rcu_exit_srcu));
-	TASKS_RCU(preempt_enable());
+	tasks_rcu_i = tasks_rcu_read_lock();
 	exit_notify(tsk, group_dead);
 	proc_exit_connector(tsk);
 #ifdef CONFIG_NUMA
@@ -805,7 +802,7 @@ void do_exit(long code)
 	if (tsk->nr_dirtied)
 		__this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied);
 	exit_rcu();
-	TASKS_RCU(__srcu_read_unlock(&tasks_rcu_exit_srcu, tasks_rcu_i));
+	tasks_rcu_read_unlock(tasks_rcu_i);
 
 	/*
 	 * The setting of TASK_RUNNING by try_to_wake_up() may be delayed