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
  ...

Documentation/RCU/checklist.rst

@@ -68,7 +68,8 @@ over a rather long period of time, but improvements are always welcome!
 	rcu_read_lock_sched(), or by the appropriate update-side lock.
 	Explicit disabling of preemption (preempt_disable(), for example)
 	can serve as rcu_read_lock_sched(), but is less readable and
-	prevents lockdep from detecting locking issues.
+	prevents lockdep from detecting locking issues.  Acquiring a
+	spinlock also enters an RCU read-side critical section.
 
 	Please note that you *cannot* rely on code known to be built
 	only in non-preemptible kernels.  Such code can and will break,
@@ -382,16 +383,17 @@ over a rather long period of time, but improvements are always welcome!
 	must use whatever locking or other synchronization is required
 	to safely access and/or modify that data structure.
 
-	Do not assume that RCU callbacks will be executed on the same
-	CPU that executed the corresponding call_rcu() or call_srcu().
-	For example, if a given CPU goes offline while having an RCU
-	callback pending, then that RCU callback will execute on some
-	surviving CPU.	(If this was not the case, a self-spawning RCU
-	callback would prevent the victim CPU from ever going offline.)
-	Furthermore, CPUs designated by rcu_nocbs= might well *always*
-	have their RCU callbacks executed on some other CPUs, in fact,
-	for some  real-time workloads, this is the whole point of using
-	the rcu_nocbs= kernel boot parameter.
+	Do not assume that RCU callbacks will be executed on
+	the same CPU that executed the corresponding call_rcu(),
+	call_srcu(), call_rcu_tasks(), call_rcu_tasks_rude(), or
+	call_rcu_tasks_trace().  For example, if a given CPU goes offline
+	while having an RCU callback pending, then that RCU callback
+	will execute on some surviving CPU.  (If this was not the case,
+	a self-spawning RCU callback would prevent the victim CPU from
+	ever going offline.)  Furthermore, CPUs designated by rcu_nocbs=
+	might well *always* have their RCU callbacks executed on some
+	other CPUs, in fact, for some  real-time workloads, this is the
+	whole point of using the rcu_nocbs= kernel boot parameter.
 
 	In addition, do not assume that callbacks queued in a given order
 	will be invoked in that order, even if they all are queued on the
@@ -444,7 +446,7 @@ over a rather long period of time, but improvements are always welcome!
 	real-time workloads than is synchronize_rcu_expedited().
 
 	It is also permissible to sleep in RCU Tasks Trace read-side
-	critical, which are delimited by rcu_read_lock_trace() and
+	critical section, which are delimited by rcu_read_lock_trace() and
 	rcu_read_unlock_trace().  However, this is a specialized flavor
 	of RCU, and you should not use it without first checking with
 	its current users.  In most cases, you should instead use SRCU.
@@ -490,6 +492,12 @@ over a rather long period of time, but improvements are always welcome!
 		since the last time that you passed that same object to
 		call_rcu() (or friends).
 
+	CONFIG_RCU_STRICT_GRACE_PERIOD:
+		combine with KASAN to check for pointers leaked out
+		of RCU read-side critical sections.  This Kconfig
+		option is tough on both performance and scalability,
+		and so is limited to four-CPU systems.
+
 	__rcu sparse checks:
 		tag the pointer to the RCU-protected data structure
 		with __rcu, and sparse will warn you if you access that

Documentation/RCU/rcu_dereference.rst

@@ -408,7 +408,10 @@ member of the rcu_dereference() to use in various situations:
 	RCU flavors, an RCU read-side critical section is entered
 	using rcu_read_lock(), anything that disables bottom halves,
 	anything that disables interrupts, or anything that disables
-	preemption.
+	preemption.  Please note that spinlock critical sections
+	are also implied RCU read-side critical sections, even when
+	they are preemptible, as they are in kernels built with
+	CONFIG_PREEMPT_RT=y.
 
 2.	If the access might be within an RCU read-side critical section
 	on the one hand, or protected by (say) my_lock on the other,

Documentation/RCU/whatisRCU.rst

@@ -172,14 +172,25 @@ rcu_read_lock()
 	critical section.  Reference counts may be used in conjunction
 	with RCU to maintain longer-term references to data structures.
 
+	Note that anything that disables bottom halves, preemption,
+	or interrupts also enters an RCU read-side critical section.
+	Acquiring a spinlock also enters an RCU read-side critical
+	sections, even for spinlocks that do not disable preemption,
+	as is the case in kernels built with CONFIG_PREEMPT_RT=y.
+	Sleeplocks do *not* enter RCU read-side critical sections.
+
 rcu_read_unlock()
 ^^^^^^^^^^^^^^^^^
 	void rcu_read_unlock(void);
 
 	This temporal primitives is used by a reader to inform the
 	reclaimer that the reader is exiting an RCU read-side critical
-	section.  Note that RCU read-side critical sections may be nested
-	and/or overlapping.
+	section.  Anything that enables bottom halves, preemption,
+	or interrupts also exits an RCU read-side critical section.
+	Releasing a spinlock also exits an RCU read-side critical section.
+
+	Note that RCU read-side critical sections may be nested and/or
+	overlapping.
 
 synchronize_rcu()
 ^^^^^^^^^^^^^^^^^
@@ -952,8 +963,8 @@ unfortunately any spinlock in a ``SLAB_TYPESAFE_BY_RCU`` object must be
 initialized after each and every call to kmem_cache_alloc(), which renders
 reference-free spinlock acquisition completely unsafe.  Therefore, when
 using ``SLAB_TYPESAFE_BY_RCU``, make proper use of a reference counter.
-(Those willing to use a kmem_cache constructor may also use locking,
-including cache-friendly sequence locking.)
+(Those willing to initialize their locks in a kmem_cache constructor
+may also use locking, including cache-friendly sequence locking.)
 
 With traditional reference counting -- such as that implemented by the
 kref library in Linux -- there is typically code that runs when the last

Documentation/admin-guide/kernel-parameters.rst

@@ -108,6 +108,7 @@ is applicable::
 	CMA	Contiguous Memory Area support is enabled.
 	DRM	Direct Rendering Management support is enabled.
 	DYNAMIC_DEBUG Build in debug messages and enable them at runtime
+	EARLY	Parameter processed too early to be embedded in initrd.
 	EDD	BIOS Enhanced Disk Drive Services (EDD) is enabled
 	EFI	EFI Partitioning (GPT) is enabled
 	EVM	Extended Verification Module

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 *);

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);				\

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

init/init_task.c

@@ -147,6 +147,7 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = {
 	.rcu_tasks_holdout = false,
 	.rcu_tasks_holdout_list = LIST_HEAD_INIT(init_task.rcu_tasks_holdout_list),
 	.rcu_tasks_idle_cpu = -1,
+	.rcu_tasks_exit_list = LIST_HEAD_INIT(init_task.rcu_tasks_exit_list),
 #endif
 #ifdef CONFIG_TASKS_TRACE_RCU
 	.trc_reader_nesting = 0,

kernel/context_tracking.c

@@ -458,6 +458,8 @@ static __always_inline void context_tracking_recursion_exit(void)
  * __ct_user_enter - Inform the context tracking that the CPU is going
  *		     to enter user or guest space mode.
  *
+ * @state: userspace context-tracking state to enter.
+ *
  * This function must be called right before we switch from the kernel
  * to user or guest space, when it's guaranteed the remaining kernel
  * instructions to execute won't use any RCU read side critical section
@@ -595,6 +597,8 @@ NOKPROBE_SYMBOL(user_enter_callable);
  * __ct_user_exit - Inform the context tracking that the CPU is
  *		    exiting user or guest mode and entering the kernel.
  *
+ * @state: userspace context-tracking state being exited from.
+ *
  * This function must be called after we entered the kernel from user or
  * guest space before any use of RCU read side critical section. This
  * potentially include any high level kernel code like syscalls, exceptions,

kernel/fork.c

@@ -1978,6 +1978,7 @@ static inline void rcu_copy_process(struct task_struct *p)
 	p->rcu_tasks_holdout = false;
 	INIT_LIST_HEAD(&p->rcu_tasks_holdout_list);
 	p->rcu_tasks_idle_cpu = -1;
+	INIT_LIST_HEAD(&p->rcu_tasks_exit_list);
 #endif /* #ifdef CONFIG_TASKS_RCU */
 #ifdef CONFIG_TASKS_TRACE_RCU
 	p->trc_reader_nesting = 0;

kernel/rcu/Kconfig

@@ -314,6 +314,19 @@ config RCU_LAZY
 	  To save power, batch RCU callbacks and flush after delay, memory
 	  pressure, or callback list growing too big.
 
+	  Requires rcu_nocbs=all to be set.
+
+	  Use rcutree.enable_rcu_lazy=0 to turn it off at boot time.
+
+config RCU_LAZY_DEFAULT_OFF
+	bool "Turn RCU lazy invocation off by default"
+	depends on RCU_LAZY
+	default n
+	help
+	  Allows building the kernel with CONFIG_RCU_LAZY=y yet keep it default
+	  off. Boot time param rcutree.enable_rcu_lazy=1 can be used to switch
+	  it back on.
+
 config RCU_DOUBLE_CHECK_CB_TIME
 	bool "RCU callback-batch backup time check"
 	depends on RCU_EXPERT

kernel/rcu/rcu.h

@@ -528,6 +528,12 @@ struct task_struct *get_rcu_tasks_gp_kthread(void);
 struct task_struct *get_rcu_tasks_rude_gp_kthread(void);
 #endif // # ifdef CONFIG_TASKS_RUDE_RCU
 
+#ifdef CONFIG_TASKS_RCU_GENERIC
+void tasks_cblist_init_generic(void);
+#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
+static inline void tasks_cblist_init_generic(void) { }
+#endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
+
 #define RCU_SCHEDULER_INACTIVE	0
 #define RCU_SCHEDULER_INIT	1
 #define RCU_SCHEDULER_RUNNING	2
@@ -543,11 +549,11 @@ enum rcutorture_type {
 };
 
 #if defined(CONFIG_RCU_LAZY)
-unsigned long rcu_lazy_get_jiffies_till_flush(void);
-void rcu_lazy_set_jiffies_till_flush(unsigned long j);
+unsigned long rcu_get_jiffies_lazy_flush(void);
+void rcu_set_jiffies_lazy_flush(unsigned long j);
 #else
-static inline unsigned long rcu_lazy_get_jiffies_till_flush(void) { return 0; }
-static inline void rcu_lazy_set_jiffies_till_flush(unsigned long j) { }
+static inline unsigned long rcu_get_jiffies_lazy_flush(void) { return 0; }
+static inline void rcu_set_jiffies_lazy_flush(unsigned long j) { }
 #endif
 
 #if defined(CONFIG_TREE_RCU)
@@ -623,12 +629,7 @@ int rcu_get_gp_kthreads_prio(void);
 void rcu_fwd_progress_check(unsigned long j);
 void rcu_force_quiescent_state(void);
 extern struct workqueue_struct *rcu_gp_wq;
-#ifdef CONFIG_RCU_EXP_KTHREAD
 extern struct kthread_worker *rcu_exp_gp_kworker;
-extern struct kthread_worker *rcu_exp_par_gp_kworker;
-#else /* !CONFIG_RCU_EXP_KTHREAD */
-extern struct workqueue_struct *rcu_par_gp_wq;
-#endif /* CONFIG_RCU_EXP_KTHREAD */
 void rcu_gp_slow_register(atomic_t *rgssp);
 void rcu_gp_slow_unregister(atomic_t *rgssp);
 #endif /* #else #ifdef CONFIG_TINY_RCU */

kernel/rcu/rcuscale.c

@@ -764,9 +764,9 @@ kfree_scale_init(void)
 
 	if (kfree_by_call_rcu) {
 		/* do a test to check the timeout. */
-		orig_jif = rcu_lazy_get_jiffies_till_flush();
+		orig_jif = rcu_get_jiffies_lazy_flush();
 
-		rcu_lazy_set_jiffies_till_flush(2 * HZ);
+		rcu_set_jiffies_lazy_flush(2 * HZ);
 		rcu_barrier();
 
 		jif_start = jiffies;
@@ -775,7 +775,7 @@ kfree_scale_init(void)
 
 		smp_cond_load_relaxed(&rcu_lazy_test1_cb_called, VAL == 1);
 
-		rcu_lazy_set_jiffies_till_flush(orig_jif);
+		rcu_set_jiffies_lazy_flush(orig_jif);
 
 		if (WARN_ON_ONCE(jiffies_at_lazy_cb - jif_start < 2 * HZ)) {
 			pr_alert("ERROR: call_rcu() CBs are not being lazy as expected!\n");

kernel/rcu/rcutorture.c

@@ -1368,9 +1368,13 @@ rcu_torture_writer(void *arg)
 	struct rcu_torture *rp;
 	struct rcu_torture *old_rp;
 	static DEFINE_TORTURE_RANDOM(rand);
+	unsigned long stallsdone = jiffies;
 	bool stutter_waited;
 	unsigned long ulo[NUM_ACTIVE_RCU_POLL_OLDSTATE];
 
+	// If a new stall test is added, this must be adjusted.
+	if (stall_cpu_holdoff + stall_gp_kthread + stall_cpu)
+		stallsdone += (stall_cpu_holdoff + stall_gp_kthread + stall_cpu + 60) * HZ;
 	VERBOSE_TOROUT_STRING("rcu_torture_writer task started");
 	if (!can_expedite)
 		pr_alert("%s" TORTURE_FLAG
@@ -1576,11 +1580,11 @@ rcu_torture_writer(void *arg)
 		    !atomic_read(&rcu_fwd_cb_nodelay) &&
 		    !cur_ops->slow_gps &&
 		    !torture_must_stop() &&
-		    boot_ended)
+		    boot_ended &&
+		    time_after(jiffies, stallsdone))
 			for (i = 0; i < ARRAY_SIZE(rcu_tortures); i++)
 				if (list_empty(&rcu_tortures[i].rtort_free) &&
-				    rcu_access_pointer(rcu_torture_current) !=
-				    &rcu_tortures[i]) {
+				    rcu_access_pointer(rcu_torture_current) != &rcu_tortures[i]) {
 					tracing_off();
 					show_rcu_gp_kthreads();
 					WARN(1, "%s: rtort_pipe_count: %d\n", __func__, rcu_tortures[i].rtort_pipe_count);
@@ -2441,7 +2445,8 @@ static struct notifier_block rcu_torture_stall_block = {
 
 /*
  * CPU-stall kthread.  It waits as specified by stall_cpu_holdoff, then
- * induces a CPU stall for the time specified by stall_cpu.
+ * induces a CPU stall for the time specified by stall_cpu.  If a new
+ * stall test is added, stallsdone in rcu_torture_writer() must be adjusted.
  */
 static int rcu_torture_stall(void *args)
 {

kernel/rcu/srcutree.c

@@ -1234,11 +1234,20 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
 	if (rhp)
 		rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
 	/*
-	 * The snapshot for acceleration must be taken _before_ the read of the
-	 * current gp sequence used for advancing, otherwise advancing may fail
-	 * and acceleration may then fail too.
+	 * It's crucial to capture the snapshot 's' for acceleration before
+	 * reading the current gp_seq that is used for advancing. This is
+	 * essential because if the acceleration snapshot is taken after a
+	 * failed advancement attempt, there's a risk that a grace period may
+	 * conclude and a new one may start in the interim. If the snapshot is
+	 * captured after this sequence of events, the acceleration snapshot 's'
+	 * could be excessively advanced, leading to acceleration failure.
+	 * In such a scenario, an 'acceleration leak' can occur, where new
+	 * callbacks become indefinitely stuck in the RCU_NEXT_TAIL segment.
+	 * Also note that encountering advancing failures is a normal
+	 * occurrence when the grace period for RCU_WAIT_TAIL is in progress.
 	 *
-	 * This could happen if:
+	 * To see this, consider the following events which occur if
+	 * rcu_seq_snap() were to be called after advance:
 	 *
 	 *  1) The RCU_WAIT_TAIL segment has callbacks (gp_num = X + 4) and the
 	 *     RCU_NEXT_READY_TAIL also has callbacks (gp_num = X + 8).
@@ -1264,6 +1273,13 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
 	if (rhp) {
 		rcu_segcblist_advance(&sdp->srcu_cblist,
 				      rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq));
+		/*
+		 * Acceleration can never fail because the base current gp_seq
+		 * used for acceleration is <= the value of gp_seq used for
+		 * advancing. This means that RCU_NEXT_TAIL segment will
+		 * always be able to be emptied by the acceleration into the
+		 * RCU_NEXT_READY_TAIL or RCU_WAIT_TAIL segments.
+		 */
 		WARN_ON_ONCE(!rcu_segcblist_accelerate(&sdp->srcu_cblist, s));
 	}
 	if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {

kernel/rcu/sync.c

@@ -24,22 +24,6 @@ void rcu_sync_init(struct rcu_sync *rsp)
 	init_waitqueue_head(&rsp->gp_wait);
 }
 
-/**
- * rcu_sync_enter_start - Force readers onto slow path for multiple updates
- * @rsp: Pointer to rcu_sync structure to use for synchronization
- *
- * Must be called after rcu_sync_init() and before first use.
- *
- * Ensures rcu_sync_is_idle() returns false and rcu_sync_{enter,exit}()
- * pairs turn into NO-OPs.
- */
-void rcu_sync_enter_start(struct rcu_sync *rsp)
-{
-	rsp->gp_count++;
-	rsp->gp_state = GP_PASSED;
-}
-
-
 static void rcu_sync_func(struct rcu_head *rhp);
 
 static void rcu_sync_call(struct rcu_sync *rsp)

kernel/rcu/tiny.c

@@ -261,4 +261,5 @@ void __init rcu_init(void)
 {
 	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 	rcu_early_boot_tests();
+	tasks_cblist_init_generic();
 }

kernel/rcu/tree.h

@@ -21,14 +21,10 @@
 
 #include "rcu_segcblist.h"
 
-/* Communicate arguments to a workqueue handler. */
+/* Communicate arguments to a kthread worker handler. */
 struct rcu_exp_work {
 	unsigned long rew_s;
-#ifdef CONFIG_RCU_EXP_KTHREAD
 	struct kthread_work rew_work;
-#else
-	struct work_struct rew_work;
-#endif /* CONFIG_RCU_EXP_KTHREAD */
 };
 
 /* RCU's kthread states for tracing. */
@@ -72,6 +68,9 @@ struct rcu_node {
 				/* Online CPUs for next expedited GP. */
 				/*  Any CPU that has ever been online will */
 				/*  have its bit set. */
+	struct kthread_worker *exp_kworker;
+				/* Workers performing per node expedited GP */
+				/* initialization. */
 	unsigned long cbovldmask;
 				/* CPUs experiencing callback overload. */
 	unsigned long ffmask;	/* Fully functional CPUs. */
@@ -113,7 +112,7 @@ struct rcu_node {
 				/*  side effect, not as a lock. */
 	unsigned long boost_time;
 				/* When to start boosting (jiffies). */
-	struct mutex boost_kthread_mutex;
+	struct mutex kthread_mutex;
 				/* Exclusion for thread spawning and affinity */
 				/*  manipulation. */
 	struct task_struct *boost_kthread_task;
@@ -467,11 +466,10 @@ static void rcu_init_one_nocb(struct rcu_node *rnp);
 static bool wake_nocb_gp(struct rcu_data *rdp, bool force);
 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 				  unsigned long j, bool lazy);
-static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
-				bool *was_alldone, unsigned long flags,
-				bool lazy);
-static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
-				 unsigned long flags);
+static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
+			  rcu_callback_t func, unsigned long flags, bool lazy);
+static void __maybe_unused __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
+						unsigned long flags);
 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level);
 static bool do_nocb_deferred_wakeup(struct rcu_data *rdp);
 static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);

kernel/rcu/tree_exp.h

@@ -198,10 +198,9 @@ static void __rcu_report_exp_rnp(struct rcu_node *rnp,
 		}
 		if (rnp->parent == NULL) {
 			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-			if (wake) {
-				smp_mb(); /* EGP done before wake_up(). */
+			if (wake)
 				swake_up_one_online(&rcu_state.expedited_wq);
-			}
+
 			break;
 		}
 		mask = rnp->grpmask;
@@ -419,7 +418,6 @@ static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp)
 
 static void rcu_exp_sel_wait_wake(unsigned long s);
 
-#ifdef CONFIG_RCU_EXP_KTHREAD
 static void sync_rcu_exp_select_node_cpus(struct kthread_work *wp)
 {
 	struct rcu_exp_work *rewp =
@@ -428,9 +426,14 @@ static void sync_rcu_exp_select_node_cpus(struct kthread_work *wp)
 	__sync_rcu_exp_select_node_cpus(rewp);
 }
 
-static inline bool rcu_gp_par_worker_started(void)
+static inline bool rcu_exp_worker_started(void)
+{
+	return !!READ_ONCE(rcu_exp_gp_kworker);
+}
+
+static inline bool rcu_exp_par_worker_started(struct rcu_node *rnp)
 {
-	return !!READ_ONCE(rcu_exp_par_gp_kworker);
+	return !!READ_ONCE(rnp->exp_kworker);
 }
 
 static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
@@ -441,7 +444,7 @@ static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
 	 * another work item on the same kthread worker can result in
 	 * deadlock.
 	 */
-	kthread_queue_work(rcu_exp_par_gp_kworker, &rnp->rew.rew_work);
+	kthread_queue_work(READ_ONCE(rnp->exp_kworker), &rnp->rew.rew_work);
 }
 
 static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
@@ -466,64 +469,6 @@ static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew
 	kthread_queue_work(rcu_exp_gp_kworker, &rew->rew_work);
 }
 
-static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
-{
-}
-#else /* !CONFIG_RCU_EXP_KTHREAD */
-static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
-{
-	struct rcu_exp_work *rewp =
-		container_of(wp, struct rcu_exp_work, rew_work);
-
-	__sync_rcu_exp_select_node_cpus(rewp);
-}
-
-static inline bool rcu_gp_par_worker_started(void)
-{
-	return !!READ_ONCE(rcu_par_gp_wq);
-}
-
-static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
-{
-	int cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
-
-	INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
-	/* If all offline, queue the work on an unbound CPU. */
-	if (unlikely(cpu > rnp->grphi - rnp->grplo))
-		cpu = WORK_CPU_UNBOUND;
-	else
-		cpu += rnp->grplo;
-	queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
-}
-
-static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
-{
-	flush_work(&rnp->rew.rew_work);
-}
-
-/*
- * Work-queue handler to drive an expedited grace period forward.
- */
-static void wait_rcu_exp_gp(struct work_struct *wp)
-{
-	struct rcu_exp_work *rewp;
-
-	rewp = container_of(wp, struct rcu_exp_work, rew_work);
-	rcu_exp_sel_wait_wake(rewp->rew_s);
-}
-
-static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
-{
-	INIT_WORK_ONSTACK(&rew->rew_work, wait_rcu_exp_gp);
-	queue_work(rcu_gp_wq, &rew->rew_work);
-}
-
-static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
-{
-	destroy_work_on_stack(&rew->rew_work);
-}
-#endif /* CONFIG_RCU_EXP_KTHREAD */
-
 /*
  * Select the nodes that the upcoming expedited grace period needs
  * to wait for.
@@ -541,7 +486,7 @@ static void sync_rcu_exp_select_cpus(void)
 		rnp->exp_need_flush = false;
 		if (!READ_ONCE(rnp->expmask))
 			continue; /* Avoid early boot non-existent wq. */
-		if (!rcu_gp_par_worker_started() ||
+		if (!rcu_exp_par_worker_started(rnp) ||
 		    rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
 		    rcu_is_last_leaf_node(rnp)) {
 			/* No worker started yet or last leaf, do direct call. */
@@ -956,7 +901,6 @@ static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
  */
 void synchronize_rcu_expedited(void)
 {
-	bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT);
 	unsigned long flags;
 	struct rcu_exp_work rew;
 	struct rcu_node *rnp;
@@ -996,7 +940,7 @@ void synchronize_rcu_expedited(void)
 		return;  /* Someone else did our work for us. */
 
 	/* Ensure that load happens before action based on it. */
-	if (unlikely(boottime)) {
+	if (unlikely((rcu_scheduler_active == RCU_SCHEDULER_INIT) || !rcu_exp_worker_started())) {
 		/* Direct call during scheduler init and early_initcalls(). */
 		rcu_exp_sel_wait_wake(s);
 	} else {
@@ -1013,9 +957,6 @@ void synchronize_rcu_expedited(void)
 
 	/* Let the next expedited grace period start. */
 	mutex_unlock(&rcu_state.exp_mutex);
-
-	if (likely(!boottime))
-		synchronize_rcu_expedited_destroy_work(&rew);
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
 

kernel/rcu/tree_nocb.h

@@ -256,6 +256,7 @@ static bool wake_nocb_gp(struct rcu_data *rdp, bool force)
 	return __wake_nocb_gp(rdp_gp, rdp, force, flags);
 }
 
+#ifdef CONFIG_RCU_LAZY
 /*
  * LAZY_FLUSH_JIFFIES decides the maximum amount of time that
  * can elapse before lazy callbacks are flushed. Lazy callbacks
@@ -264,21 +265,20 @@ static bool wake_nocb_gp(struct rcu_data *rdp, bool force)
  * left unsubmitted to RCU after those many jiffies.
  */
 #define LAZY_FLUSH_JIFFIES (10 * HZ)
-static unsigned long jiffies_till_flush = LAZY_FLUSH_JIFFIES;
+static unsigned long jiffies_lazy_flush = LAZY_FLUSH_JIFFIES;
 
-#ifdef CONFIG_RCU_LAZY
 // To be called only from test code.
-void rcu_lazy_set_jiffies_till_flush(unsigned long jif)
+void rcu_set_jiffies_lazy_flush(unsigned long jif)
 {
-	jiffies_till_flush = jif;
+	jiffies_lazy_flush = jif;
 }
-EXPORT_SYMBOL(rcu_lazy_set_jiffies_till_flush);
+EXPORT_SYMBOL(rcu_set_jiffies_lazy_flush);
 
-unsigned long rcu_lazy_get_jiffies_till_flush(void)
+unsigned long rcu_get_jiffies_lazy_flush(void)
 {
-	return jiffies_till_flush;
+	return jiffies_lazy_flush;
 }
-EXPORT_SYMBOL(rcu_lazy_get_jiffies_till_flush);
+EXPORT_SYMBOL(rcu_get_jiffies_lazy_flush);
 #endif
 
 /*
@@ -299,7 +299,7 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
 	 */
 	if (waketype == RCU_NOCB_WAKE_LAZY &&
 	    rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) {
-		mod_timer(&rdp_gp->nocb_timer, jiffies + jiffies_till_flush);
+		mod_timer(&rdp_gp->nocb_timer, jiffies + rcu_get_jiffies_lazy_flush());
 		WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
 	} else if (waketype == RCU_NOCB_WAKE_BYPASS) {
 		mod_timer(&rdp_gp->nocb_timer, jiffies + 2);
@@ -482,7 +482,7 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 	// flush ->nocb_bypass to ->cblist.
 	if ((ncbs && !bypass_is_lazy && j != READ_ONCE(rdp->nocb_bypass_first)) ||
 	    (ncbs &&  bypass_is_lazy &&
-	     (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush))) ||
+	     (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + rcu_get_jiffies_lazy_flush()))) ||
 	    ncbs >= qhimark) {
 		rcu_nocb_lock(rdp);
 		*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
@@ -532,9 +532,7 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 	// 2. Both of these conditions are met:
 	//    a. The bypass list previously had only lazy CBs, and:
 	//    b. The new CB is non-lazy.
-	if (ncbs && (!bypass_is_lazy || lazy)) {
-		local_irq_restore(flags);
-	} else {
+	if (!ncbs || (bypass_is_lazy && !lazy)) {
 		// No-CBs GP kthread might be indefinitely asleep, if so, wake.
 		rcu_nocb_lock(rdp); // Rare during call_rcu() flood.
 		if (!rcu_segcblist_pend_cbs(&rdp->cblist)) {
@@ -544,7 +542,7 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 		} else {
 			trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
 					    TPS("FirstBQnoWake"));
-			rcu_nocb_unlock_irqrestore(rdp, flags);
+			rcu_nocb_unlock(rdp);
 		}
 	}
 	return true; // Callback already enqueued.
@@ -566,11 +564,12 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
 	long lazy_len;
 	long len;
 	struct task_struct *t;
+	struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
 
 	// If we are being polled or there is no kthread, just leave.
 	t = READ_ONCE(rdp->nocb_gp_kthread);
 	if (rcu_nocb_poll || !t) {
-		rcu_nocb_unlock_irqrestore(rdp, flags);
+		rcu_nocb_unlock(rdp);
 		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
 				    TPS("WakeNotPoll"));
 		return;
@@ -583,17 +582,17 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
 		rdp->qlen_last_fqs_check = len;
 		// Only lazy CBs in bypass list
 		if (lazy_len && bypass_len == lazy_len) {
-			rcu_nocb_unlock_irqrestore(rdp, flags);
+			rcu_nocb_unlock(rdp);
 			wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_LAZY,
 					   TPS("WakeLazy"));
 		} else if (!irqs_disabled_flags(flags)) {
 			/* ... if queue was empty ... */
-			rcu_nocb_unlock_irqrestore(rdp, flags);
+			rcu_nocb_unlock(rdp);
 			wake_nocb_gp(rdp, false);
 			trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
 					    TPS("WakeEmpty"));
 		} else {
-			rcu_nocb_unlock_irqrestore(rdp, flags);
+			rcu_nocb_unlock(rdp);
 			wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
 					   TPS("WakeEmptyIsDeferred"));
 		}
@@ -610,20 +609,32 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
 		smp_mb(); /* Enqueue before timer_pending(). */
 		if ((rdp->nocb_cb_sleep ||
 		     !rcu_segcblist_ready_cbs(&rdp->cblist)) &&
-		    !timer_pending(&rdp->nocb_timer)) {
-			rcu_nocb_unlock_irqrestore(rdp, flags);
+		    !timer_pending(&rdp_gp->nocb_timer)) {
+			rcu_nocb_unlock(rdp);
 			wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
 					   TPS("WakeOvfIsDeferred"));
 		} else {
-			rcu_nocb_unlock_irqrestore(rdp, flags);
+			rcu_nocb_unlock(rdp);
 			trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
 		}
 	} else {
-		rcu_nocb_unlock_irqrestore(rdp, flags);
+		rcu_nocb_unlock(rdp);
 		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
 	}
 }
 
+static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
+			  rcu_callback_t func, unsigned long flags, bool lazy)
+{
+	bool was_alldone;
+
+	if (!rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy)) {
+		/* Not enqueued on bypass but locked, do regular enqueue */
+		rcutree_enqueue(rdp, head, func);
+		__call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
+	}
+}
+
 static int nocb_gp_toggle_rdp(struct rcu_data *rdp,
 			       bool *wake_state)
 {
@@ -723,7 +734,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 		lazy_ncbs = READ_ONCE(rdp->lazy_len);
 
 		if (bypass_ncbs && (lazy_ncbs == bypass_ncbs) &&
-		    (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush) ||
+		    (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + rcu_get_jiffies_lazy_flush()) ||
 		     bypass_ncbs > 2 * qhimark)) {
 			flush_bypass = true;
 		} else if (bypass_ncbs && (lazy_ncbs != bypass_ncbs) &&
@@ -779,7 +790,6 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 		if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
 			needwake = rdp->nocb_cb_sleep;
 			WRITE_ONCE(rdp->nocb_cb_sleep, false);
-			smp_mb(); /* CB invocation -after- GP end. */
 		} else {
 			needwake = false;
 		}
@@ -933,8 +943,7 @@ static void nocb_cb_wait(struct rcu_data *rdp)
 		swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
 						    nocb_cb_wait_cond(rdp));
 
-		// VVV Ensure CB invocation follows _sleep test.
-		if (smp_load_acquire(&rdp->nocb_cb_sleep)) { // ^^^
+		if (READ_ONCE(rdp->nocb_cb_sleep)) {
 			WARN_ON(signal_pending(current));
 			trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
 		}
@@ -1383,7 +1392,7 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 			rcu_nocb_unlock_irqrestore(rdp, flags);
 			continue;
 		}
-		WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false));
+		rcu_nocb_try_flush_bypass(rdp, jiffies);
 		rcu_nocb_unlock_irqrestore(rdp, flags);
 		wake_nocb_gp(rdp, false);
 		sc->nr_to_scan -= _count;
@@ -1768,10 +1777,10 @@ static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 	return true;
 }
 
-static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
-				bool *was_alldone, unsigned long flags, bool lazy)
+static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
+			  rcu_callback_t func, unsigned long flags, bool lazy)
 {
-	return false;
+	WARN_ON_ONCE(1);  /* Should be dead code! */
 }
 
 static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,

kernel/rcu/tree_plugin.h

@@ -1195,14 +1195,13 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
 	struct sched_param sp;
 	struct task_struct *t;
 
-	mutex_lock(&rnp->boost_kthread_mutex);
-	if (rnp->boost_kthread_task || !rcu_scheduler_fully_active)
-		goto out;
+	if (rnp->boost_kthread_task)
+		return;
 
 	t = kthread_create(rcu_boost_kthread, (void *)rnp,
 			   "rcub/%d", rnp_index);
 	if (WARN_ON_ONCE(IS_ERR(t)))
-		goto out;
+		return;
 
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
 	rnp->boost_kthread_task = t;
@@ -1210,48 +1209,11 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
 	sp.sched_priority = kthread_prio;
 	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
 	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
-
- out:
-	mutex_unlock(&rnp->boost_kthread_mutex);
 }
 
-/*
- * Set the per-rcu_node kthread's affinity to cover all CPUs that are
- * served by the rcu_node in question.  The CPU hotplug lock is still
- * held, so the value of rnp->qsmaskinit will be stable.
- *
- * We don't include outgoingcpu in the affinity set, use -1 if there is
- * no outgoing CPU.  If there are no CPUs left in the affinity set,
- * this function allows the kthread to execute on any CPU.
- *
- * Any future concurrent calls are serialized via ->boost_kthread_mutex.
- */
-static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+static struct task_struct *rcu_boost_task(struct rcu_node *rnp)
 {
-	struct task_struct *t = rnp->boost_kthread_task;
-	unsigned long mask;
-	cpumask_var_t cm;
-	int cpu;
-
-	if (!t)
-		return;
-	if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
-		return;
-	mutex_lock(&rnp->boost_kthread_mutex);
-	mask = rcu_rnp_online_cpus(rnp);
-	for_each_leaf_node_possible_cpu(rnp, cpu)
-		if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
-		    cpu != outgoingcpu)
-			cpumask_set_cpu(cpu, cm);
-	cpumask_and(cm, cm, housekeeping_cpumask(HK_TYPE_RCU));
-	if (cpumask_empty(cm)) {
-		cpumask_copy(cm, housekeeping_cpumask(HK_TYPE_RCU));
-		if (outgoingcpu >= 0)
-			cpumask_clear_cpu(outgoingcpu, cm);
-	}
-	set_cpus_allowed_ptr(t, cm);
-	mutex_unlock(&rnp->boost_kthread_mutex);
-	free_cpumask_var(cm);
+	return READ_ONCE(rnp->boost_kthread_task);
 }
 
 #else /* #ifdef CONFIG_RCU_BOOST */
@@ -1270,10 +1232,10 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
 {
 }
 
-static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+static struct task_struct *rcu_boost_task(struct rcu_node *rnp)
 {
+	return NULL;
 }
-
 #endif /* #else #ifdef CONFIG_RCU_BOOST */
 
 /*