Merge tag 'rcu.next.v6.9' of git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux

Pull RCU updates from Boqun Feng:

 - Eliminate deadlocks involving do_exit() and RCU tasks, by Paul:
   Instead of SRCU read side critical sections, now a percpu list is
   used in do_exit() for scaning yet-to-exit tasks

 - Fix a deadlock due to the dependency between workqueue and RCU
   expedited grace period, reported by Anna-Maria Behnsen and Thomas
   Gleixner and fixed by Frederic: Now RCU expedited always uses its own
   kthread worker instead of a workqueue

 - RCU NOCB updates, code cleanups, unnecessary barrier removals and
   minor bug fixes

 - Maintain real-time response in rcu_tasks_postscan() and a minor fix
   for tasks trace quiescence check

 - Misc updates, comments and readibility improvement, boot time
   parameter for lazy RCU and rcutorture improvement

 - Documentation updates

* tag 'rcu.next.v6.9' of git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux: (34 commits)
  rcu-tasks: Maintain real-time response in rcu_tasks_postscan()
  rcu-tasks: Eliminate deadlocks involving do_exit() and RCU tasks
  rcu-tasks: Maintain lists to eliminate RCU-tasks/do_exit() deadlocks
  rcu-tasks: Initialize data to eliminate RCU-tasks/do_exit() deadlocks
  rcu-tasks: Initialize callback lists at rcu_init() time
  rcu-tasks: Add data to eliminate RCU-tasks/do_exit() deadlocks
  rcu-tasks: Repair RCU Tasks Trace quiescence check
  rcu/sync: remove un-used rcu_sync_enter_start function
  rcutorture: Suppress rtort_pipe_count warnings until after stalls
  srcu: Improve comments about acceleration leak
  rcu: Provide a boot time parameter to control lazy RCU
  rcu: Rename jiffies_till_flush to jiffies_lazy_flush
  doc: Update checklist.rst discussion of callback execution
  doc: Clarify use of slab constructors and SLAB_TYPESAFE_BY_RCU
  context_tracking: Fix kerneldoc headers for __ct_user_{enter,exit}()
  doc: Add EARLY flag to early-parsed kernel boot parameters
  doc: Add CONFIG_RCU_STRICT_GRACE_PERIOD to checklist.rst
  doc: Make checklist.rst note that spinlocks are implied RCU readers
  doc: Make whatisRCU.rst note that spinlocks are RCU readers
  doc: Spinlocks are implied RCU readers
  ...

3 files changed, 4 insertions, 3 deletions

diff --git a/include/linux/rcu_sync.h b/include/linux/rcu_sync.h
index 0027d4c8087c..3860dbb9107a 100644
--- a/include/linux/rcu_sync.h
+++ b/include/linux/rcu_sync.h
@@ -37,7 +37,6 @@ static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
 }
 
 extern void rcu_sync_init(struct rcu_sync *);
-extern void rcu_sync_enter_start(struct rcu_sync *);
 extern void rcu_sync_enter(struct rcu_sync *);
 extern void rcu_sync_exit(struct rcu_sync *);
 extern void rcu_sync_dtor(struct rcu_sync *);
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 0746b1b0b663..16f519914415 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -184,9 +184,9 @@ void rcu_tasks_trace_qs_blkd(struct task_struct *t);
 	do {									\
 		int ___rttq_nesting = READ_ONCE((t)->trc_reader_nesting);	\
 										\
-		if (likely(!READ_ONCE((t)->trc_reader_special.b.need_qs)) &&	\
+		if (unlikely(READ_ONCE((t)->trc_reader_special.b.need_qs) == TRC_NEED_QS) &&	\
 		    likely(!___rttq_nesting)) {					\
-			rcu_trc_cmpxchg_need_qs((t), 0,	TRC_NEED_QS_CHECKED);	\
+			rcu_trc_cmpxchg_need_qs((t), TRC_NEED_QS, TRC_NEED_QS_CHECKED);	\
 		} else if (___rttq_nesting && ___rttq_nesting != INT_MIN &&	\
 			   !READ_ONCE((t)->trc_reader_special.b.blocked)) {	\
 			rcu_tasks_trace_qs_blkd(t);				\
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 15b7cb478d16..17cb0761ff65 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -858,6 +858,8 @@ struct task_struct {
 	u8				rcu_tasks_idx;
 	int				rcu_tasks_idle_cpu;
 	struct list_head		rcu_tasks_holdout_list;
+	int				rcu_tasks_exit_cpu;
+	struct list_head		rcu_tasks_exit_list;
 #endif /* #ifdef CONFIG_TASKS_RCU */
 
 #ifdef CONFIG_TASKS_TRACE_RCU