[PATCH tip/core/rcu 0/8] Miscellaneous fixes for v5.1

[PATCH tip/core/rcu 0/8] Miscellaneous fixes for v5.1

[Paul E. McKenney]

Hello!

This series contains miscellaneous fixes:

1.	Add docbook for rcu_head_init() and rcu_head_after_call_rcu().

2.	Rename rcu_check_callbacks() to rcu_sched_clock_irq().

3.	Rename rcu_process_callbacks() to rcu_core() for Tree RCU.

4.	Remove preemption disabling from expedited CPU selection.

5.	Repair rcu_nmi_exit() docbook header.

6.	Fix obsolete DYNTICK_IRQ_NONIDLE comment.

7.	Add sparse check to rcu_assign_pointer(), courtesy of Joel
	Fernandes.

8.	Move CONTEXT_TRACKING Kconfig option to kernel/time/Kconfig.

							Thanx, Paul

------------------------------------------------------------------------

 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html   |    6 +-
 Documentation/RCU/Design/Memory-Ordering/TreeRCU-callback-invocation.svg |    2 
 Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg                  |    8 +-
 Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg                  |    6 +-
 include/linux/rcupdate.h                                                 |   21 +++----
 kernel/rcu/Kconfig                                                       |   30 ----------
 kernel/rcu/rcu.h                                                         |    2 
 kernel/rcu/tiny.c                                                        |    2 
 kernel/rcu/tree.c                                                        |   29 ++++-----
 kernel/rcu/tree.h                                                        |    2 
 kernel/rcu/tree_exp.h                                                    |    2 
 kernel/rcu/tree_plugin.h                                                 |   24 +++-----
 kernel/time/Kconfig                                                      |   29 +++++++++
 kernel/time/timer.c                                                      |    2 
 14 files changed, 77 insertions(+), 88 deletions(-)

[PATCH tip/core/rcu 1/8] rcu: Docbook for rcu_head_init() and rcu_head_after_call_rcu()

[Paul E. McKenney]

This commit adds the missing asterisks required to make Sphinx pick up
the current header comments for these two functions.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
 include/linux/rcupdate.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 4db8bcacc51a..d8a8302e21f0 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -859,7 +859,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
 
 /* Has the specified rcu_head structure been handed to call_rcu()? */
 
-/*
+/**
  * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
  * @rhp: The rcu_head structure to initialize.
  *
@@ -874,10 +874,10 @@ static inline void rcu_head_init(struct rcu_head *rhp)
 	rhp->func = (rcu_callback_t)~0L;
 }
 
-/*
+/**
  * rcu_head_after_call_rcu - Has this rcu_head been passed to call_rcu()?
  * @rhp: The rcu_head structure to test.
- * @func: The function passed to call_rcu() along with @rhp.
+ * @f: The function passed to call_rcu() along with @rhp.
  *
  * Returns @true if the @rhp has been passed to call_rcu() with @func,
  * and @false otherwise.  Emits a warning in any other case, including
-- 
2.17.1

[PATCH tip/core/rcu 2/8] rcu: Rename rcu_check_callbacks() to rcu_sched_clock_irq()

[Paul E. McKenney]

The name rcu_check_callbacks() arguably made sense back in the early
2000s when RCU was quite a bit simpler than it is today, but it has
become quite misleading, especially with the advent of dyntick-idle
and NO_HZ_FULL.  The rcu_check_callbacks() function is RCU's hook into
the scheduling-clock interrupt, and is now but one of many ways that
callbacks get promoted to invocable state.

This commit therefore changes the name to rcu_sched_clock_irq(),
which is the same number of characters and clearly indicates this
function's relation to the rest of the Linux kernel.  In addition, for
the sake of consistency, rcu_flavor_check_callbacks() is also renamed
to rcu_flavor_sched_clock_irq().

While in the area, the header comments for both functions are reworked.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
 .../Tree-RCU-Memory-Ordering.html             |  4 ++--
 .../TreeRCU-callback-invocation.svg           |  2 +-
 .../RCU/Design/Memory-Ordering/TreeRCU-gp.svg |  4 ++--
 .../RCU/Design/Memory-Ordering/TreeRCU-qs.svg |  2 +-
 include/linux/rcupdate.h                      |  2 +-
 kernel/rcu/tiny.c                             |  2 +-
 kernel/rcu/tree.c                             | 18 +++++++-------
 kernel/rcu/tree.h                             |  2 +-
 kernel/rcu/tree_plugin.h                      | 24 ++++++++-----------
 kernel/time/timer.c                           |  2 +-
 10 files changed, 29 insertions(+), 33 deletions(-)

diff --git a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html
index e4d94fba6c89..a3acfd49255f 100644
--- a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html
+++ b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html
@@ -485,7 +485,7 @@ section that the grace period must wait on.
 noted by <tt>rcu_node_context_switch()</tt> on the left.
 On the other hand, if the CPU takes a scheduler-clock interrupt
 while executing in usermode, a quiescent state will be noted by
-<tt>rcu_check_callbacks()</tt> on the right.
+<tt>rcu_sched_clock_irq()</tt> on the right.
 Either way, the passage through a quiescent state will be noted
 in a per-CPU variable.
 
@@ -651,7 +651,7 @@ to end.
 These callbacks are identified by <tt>rcu_advance_cbs()</tt>,
 which is usually invoked by <tt>__note_gp_changes()</tt>.
 As shown in the diagram below, this invocation can be triggered by
-the scheduling-clock interrupt (<tt>rcu_check_callbacks()</tt> on
+the scheduling-clock interrupt (<tt>rcu_sched_clock_irq()</tt> on
 the left) or by idle entry (<tt>rcu_cleanup_after_idle()</tt> on
 the right, but only for kernels build with
 <tt>CONFIG_RCU_FAST_NO_HZ=y</tt>).
diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-callback-invocation.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-callback-invocation.svg
index 832408313d93..3fcf0c17cef2 100644
--- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-callback-invocation.svg
+++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-callback-invocation.svg
@@ -349,7 +349,7 @@
        font-weight="bold"
        font-size="192"
        id="text202-7-5"
-       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_check_callbacks()</text>
+       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_sched_clock_irq()</text>
     <rect
        x="7069.6187"
        y="5087.4678"
diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
index acd73c7ad0f4..f0bbe6f8d729 100644
--- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
+++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
@@ -3902,7 +3902,7 @@
          font-style="normal"
          y="-4418.6582"
          x="3745.7725"
-         xml:space="preserve">rcu_check_callbacks()</text>
+         xml:space="preserve">rcu_sched_clock_irq()</text>
     </g>
     <g
        transform="translate(-850.30204,55463.106)"
@@ -4968,7 +4968,7 @@
        font-weight="bold"
        font-size="192"
        id="text202-7-5-19"
-       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_check_callbacks()</text>
+       style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_sched_clock_irq()</text>
     <rect
        x="5314.2671"
        y="82817.688"
diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg
index 149bec2a4493..3596ffdd4685 100644
--- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg
+++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg
@@ -775,7 +775,7 @@
          font-style="normal"
          y="-4418.6582"
          x="3745.7725"
-         xml:space="preserve">rcu_check_callbacks()</text>
+         xml:space="preserve">rcu_sched_clock_irq()</text>
     </g>
     <g
        transform="translate(399.7744,828.86448)"
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index d8a8302e21f0..b4e99639d6d4 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -89,7 +89,7 @@ static inline int rcu_preempt_depth(void)
 /* Internal to kernel */
 void rcu_init(void);
 extern int rcu_scheduler_active __read_mostly;
-void rcu_check_callbacks(int user);
+void rcu_sched_clock_irq(int user);
 void rcu_report_dead(unsigned int cpu);
 void rcutree_migrate_callbacks(int cpu);
 
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 5f5963ba313e..d7a9135b9471 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -76,7 +76,7 @@ void rcu_qs(void)
  * be called from hardirq context.  It is normally called from the
  * scheduling-clock interrupt.
  */
-void rcu_check_callbacks(int user)
+void rcu_sched_clock_irq(int user)
 {
 	if (user) {
 		rcu_qs();
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 9180158756d2..a79dd51c9cce 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1115,7 +1115,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
 	}
 
 	/*
-	 * NO_HZ_FULL CPUs can run in-kernel without rcu_check_callbacks!
+	 * NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq!
 	 * The above code handles this, but only for straight cond_resched().
 	 * And some in-kernel loops check need_resched() before calling
 	 * cond_resched(), which defeats the above code for CPUs that are
@@ -2497,14 +2497,14 @@ static void rcu_do_batch(struct rcu_data *rdp)
 }
 
 /*
- * Check to see if this CPU is in a non-context-switch quiescent state
- * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
- * Also schedule RCU core processing.
- *
- * This function must be called from hardirq context.  It is normally
- * invoked from the scheduling-clock interrupt.
+ * This function is invoked from each scheduling-clock interrupt,
+ * and checks to see if this CPU is in a non-context-switch quiescent
+ * state, for example, user mode or idle loop.  It also schedules RCU
+ * core processing.  If the current grace period has gone on too long,
+ * it will ask the scheduler to manufacture a context switch for the sole
+ * purpose of providing a providing the needed quiescent state.
  */
-void rcu_check_callbacks(int user)
+void rcu_sched_clock_irq(int user)
 {
 	trace_rcu_utilization(TPS("Start scheduler-tick"));
 	raw_cpu_inc(rcu_data.ticks_this_gp);
@@ -2517,7 +2517,7 @@ void rcu_check_callbacks(int user)
 		}
 		__this_cpu_write(rcu_data.rcu_urgent_qs, false);
 	}
-	rcu_flavor_check_callbacks(user);
+	rcu_flavor_sched_clock_irq(user);
 	if (rcu_pending())
 		invoke_rcu_core();
 
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index d90b02b53c0e..6562411de80d 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -420,7 +420,7 @@ static void rcu_print_detail_task_stall(void);
 static int rcu_print_task_stall(struct rcu_node *rnp);
 static int rcu_print_task_exp_stall(struct rcu_node *rnp);
 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
-static void rcu_flavor_check_callbacks(int user);
+static void rcu_flavor_sched_clock_irq(int user);
 void call_rcu(struct rcu_head *head, rcu_callback_t func);
 static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck);
 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 1b3dd2fc0cd6..575671646c60 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -307,7 +307,7 @@ static void rcu_qs(void)
 				       __this_cpu_read(rcu_data.gp_seq),
 				       TPS("cpuqs"));
 		__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
-		barrier(); /* Coordinate with rcu_flavor_check_callbacks(). */
+		barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
 		current->rcu_read_unlock_special.b.need_qs = false;
 	}
 }
@@ -788,13 +788,13 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
 }
 
 /*
- * Check for a quiescent state from the current CPU.  When a task blocks,
- * the task is recorded in the corresponding CPU's rcu_node structure,
- * which is checked elsewhere.
- *
- * Caller must disable hard irqs.
+ * Check for a quiescent state from the current CPU, including voluntary
+ * context switches for Tasks RCU.  When a task blocks, the task is
+ * recorded in the corresponding CPU's rcu_node structure, which is checked
+ * elsewhere, hence this function need only check for quiescent states
+ * related to the current CPU, not to those related to tasks.
  */
-static void rcu_flavor_check_callbacks(int user)
+static void rcu_flavor_sched_clock_irq(int user)
 {
 	struct task_struct *t = current;
 
@@ -1088,14 +1088,10 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
 }
 
 /*
- * Check to see if this CPU is in a non-context-switch quiescent state
- * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
- * Also schedule RCU core processing.
- *
- * This function must be called from hardirq context.  It is normally
- * invoked from the scheduling-clock interrupt.
+ * Check to see if this CPU is in a non-context-switch quiescent state,
+ * namely user mode and idle loop.
  */
-static void rcu_flavor_check_callbacks(int user)
+static void rcu_flavor_sched_clock_irq(int user)
 {
 	if (user || rcu_is_cpu_rrupt_from_idle()) {
 
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 444156debfa0..6eb7cc4b6d52 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1632,7 +1632,7 @@ void update_process_times(int user_tick)
 	/* Note: this timer irq context must be accounted for as well. */
 	account_process_tick(p, user_tick);
 	run_local_timers();
-	rcu_check_callbacks(user_tick);
+	rcu_sched_clock_irq(user_tick);
 #ifdef CONFIG_IRQ_WORK
 	if (in_irq())
 		irq_work_tick();
-- 
2.17.1

[PATCH tip/core/rcu 3/8] rcu: Rename rcu_process_callbacks() to rcu_core() for Tree RCU

[Paul E. McKenney]

Although the name rcu_process_callbacks() still makes sense for Tiny
RCU, where most of what it does is invoke callbacks, it no longer makes
much sense for Tree RCU, especially given that the actually callback
invocation is relegated to rcu_do_batch(), or, for no-CBs CPUs, to the
rcuo kthreads.  Especially in the latter case, rcu_process_callbacks()
has very little to do with actual callbacks.  A better description of
this function is that it performs RCU's core processing.

This commit therefore changes the name of Tree RCU's rcu_process_callbacks()
function to rcu_core(), which also has the virtue of being consistent with
the existing invoke_rcu_core() function.

While in the area, the header comment is reworked.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
 .../Memory-Ordering/Tree-RCU-Memory-Ordering.html      |  2 +-
 .../RCU/Design/Memory-Ordering/TreeRCU-gp.svg          |  4 ++--
 .../RCU/Design/Memory-Ordering/TreeRCU-qs.svg          |  4 ++--
 kernel/rcu/tree.c                                      | 10 +++-------
 4 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html
index a3acfd49255f..8d21af02b1f0 100644
--- a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html
+++ b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html
@@ -491,7 +491,7 @@ in a per-CPU variable.
 
 <p>The next time an <tt>RCU_SOFTIRQ</tt> handler executes on
 this CPU (for example, after the next scheduler-clock
-interrupt), <tt>__rcu_process_callbacks()</tt> will invoke
+interrupt), <tt>rcu_core()</tt> will invoke
 <tt>rcu_check_quiescent_state()</tt>, which will notice the
 recorded quiescent state, and invoke
 <tt>rcu_report_qs_rdp()</tt>.
diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
index f0bbe6f8d729..2bcd742d6e49 100644
--- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
+++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg
@@ -3924,7 +3924,7 @@
          font-style="normal"
          y="-4418.6582"
          x="3745.7725"
-         xml:space="preserve">rcu_process_callbacks()</text>
+         xml:space="preserve">rcu_core()</text>
       <text
          style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier"
          id="text202-7-5-3-27-0"
@@ -3933,7 +3933,7 @@
          font-style="normal"
          y="-4165.7954"
          x="3745.7725"
-         xml:space="preserve">rcu_check_quiescent_state())</text>
+         xml:space="preserve">rcu_check_quiescent_state()</text>
       <text
          style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier"
          id="text202-7-5-3-27-0-9"
diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg
index 3596ffdd4685..779c9ac31a52 100644
--- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg
+++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-qs.svg
@@ -797,7 +797,7 @@
          font-style="normal"
          y="-4418.6582"
          x="3745.7725"
-         xml:space="preserve">rcu_process_callbacks()</text>
+         xml:space="preserve">rcu_core()</text>
       <text
          style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier"
          id="text202-7-5-3-27-0"
@@ -806,7 +806,7 @@
          font-style="normal"
          y="-4165.7954"
          x="3745.7725"
-         xml:space="preserve">rcu_check_quiescent_state())</text>
+         xml:space="preserve">rcu_check_quiescent_state()</text>
       <text
          style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier"
          id="text202-7-5-3-27-0-9"
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index a79dd51c9cce..36b04b41f2c9 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2711,12 +2711,8 @@ void rcu_fwd_progress_check(unsigned long j)
 }
 EXPORT_SYMBOL_GPL(rcu_fwd_progress_check);
 
-/*
- * This does the RCU core processing work for the specified rcu_data
- * structures.  This may be called only from the CPU to whom the rdp
- * belongs.
- */
-static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
+/* Perform RCU core processing work for the current CPU.  */
+static __latent_entropy void rcu_core(struct softirq_action *unused)
 {
 	unsigned long flags;
 	struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
@@ -3777,7 +3773,7 @@ void __init rcu_init(void)
 	rcu_init_one();
 	if (dump_tree)
 		rcu_dump_rcu_node_tree();
-	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+	open_softirq(RCU_SOFTIRQ, rcu_core);
 
 	/*
 	 * We don't need protection against CPU-hotplug here because
-- 
2.17.1

[PATCH tip/core/rcu 4/8] rcu: Remove preemption disabling from expedited CPU selection

[Paul E. McKenney]

It turns out that it is queue_delayed_work_on() rather than
queue_work_on() that has difficulties when used concurrently with
CPU-hotplug removal operations.  It is therefore unnecessary to protect
CPU identification and queue_work_on() with preempt_disable().

This commit therefore removes the preempt_disable() and preempt_enable()
from sync_rcu_exp_select_cpus(), which has the further benefit of reducing
the number of changes that must be maintained in the -rt patchset.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Sebastian Siewior <bigeasy@linutronix.de>
Suggested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
 kernel/rcu/tree_exp.h | 2 --
 1 file changed, 2 deletions(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 928fe5893a57..f42c999f4d2d 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -449,7 +449,6 @@ static void sync_rcu_exp_select_cpus(smp_call_func_t func)
 			continue;
 		}
 		INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
-		preempt_disable();
 		cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
 		/* If all offline, queue the work on an unbound CPU. */
 		if (unlikely(cpu > rnp->grphi - rnp->grplo))
@@ -457,7 +456,6 @@ static void sync_rcu_exp_select_cpus(smp_call_func_t func)
 		else
 			cpu += rnp->grplo;
 		queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
-		preempt_enable();
 		rnp->exp_need_flush = true;
 	}
 
-- 
2.17.1

[PATCH tip/core/rcu 5/8] rcu: Repair rcu_nmi_exit() docbook header

[Paul E. McKenney]

This commit removes the "@irq" argument from the rcu_nmi_exit() docbook
header, given that this function now has no arguments.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
 kernel/rcu/tree.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 36b04b41f2c9..ede942c2b965 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -701,7 +701,6 @@ static __always_inline void rcu_nmi_exit_common(bool irq)
 
 /**
  * rcu_nmi_exit - inform RCU of exit from NMI context
- * @irq: Is this call from rcu_irq_exit?
  *
  * If you add or remove a call to rcu_nmi_exit(), be sure to test
  * with CONFIG_RCU_EQS_DEBUG=y.
-- 
2.17.1

[PATCH tip/core/rcu 6/8] rcu: Fix obsolete DYNTICK_IRQ_NONIDLE comment

[Paul E. McKenney]

This commit updates the DYNTICK_IRQ_NONIDLE header comment to remove
the obsolete commentary about unmatched rcu_irq_{enter,exit}().

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
 kernel/rcu/rcu.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index a393e24a9195..4065a1619e0c 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -30,7 +30,7 @@
 #define RCU_TRACE(stmt)
 #endif /* #else #ifdef CONFIG_RCU_TRACE */
 
-/* Offset to allow for unmatched rcu_irq_{enter,exit}(). */
+/* Offset to allow distinguishing irq vs. task-based idle entry/exit. */
 #define DYNTICK_IRQ_NONIDLE	((LONG_MAX / 2) + 1)
 
 
-- 
2.17.1

[PATCH tip/core/rcu 7/8] rcu: Add sparse check to rcu_assign_pointer()

[Paul E. McKenney]

From: "Joel Fernandes (Google)" <joel@joelfernandes.org>

The rcu_assign_pointer() function currently doesn't do any sparse checking
on the assigned-to pointer.  So its possible that a pointer that is
not __rcu annotated is assigned with rcu_assign_pointer without sparse
complaints.  Because rcu_dereference() already does such checking,
this commit makes rcu_assign_pointer() to do the same. The extra
error could be helpful in cases where an RCU pointer is assigned with
rcu_assign_pointer() but not annotated with __rcu.

This doesn't generate any code in the normal case because __CHECKER__ is
defined only in the context of sparse.

This commit also renames rcu_dereference_sparse() to rcu_check_parse()
since the checking now happens not only during derereferencing but also
during assignment.

Test: Introduced an rcu_assign_pointer in code and checked the output of
sparse with and without this change. The change correctly causes sparse
to throw an error.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
 include/linux/rcupdate.h | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index b4e99639d6d4..0bb5d906bff3 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -309,16 +309,16 @@ static inline void rcu_preempt_sleep_check(void) { }
  */
 
 #ifdef __CHECKER__
-#define rcu_dereference_sparse(p, space) \
+#define rcu_check_sparse(p, space) \
 	((void)(((typeof(*p) space *)p) == p))
 #else /* #ifdef __CHECKER__ */
-#define rcu_dereference_sparse(p, space)
+#define rcu_check_sparse(p, space)
 #endif /* #else #ifdef __CHECKER__ */
 
 #define __rcu_access_pointer(p, space) \
 ({ \
 	typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
-	rcu_dereference_sparse(p, space); \
+	rcu_check_sparse(p, space); \
 	((typeof(*p) __force __kernel *)(_________p1)); \
 })
 #define __rcu_dereference_check(p, c, space) \
@@ -326,13 +326,13 @@ static inline void rcu_preempt_sleep_check(void) { }
 	/* Dependency order vs. p above. */ \
 	typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
 	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
-	rcu_dereference_sparse(p, space); \
+	rcu_check_sparse(p, space); \
 	((typeof(*p) __force __kernel *)(________p1)); \
 })
 #define __rcu_dereference_protected(p, c, space) \
 ({ \
 	RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
-	rcu_dereference_sparse(p, space); \
+	rcu_check_sparse(p, space); \
 	((typeof(*p) __force __kernel *)(p)); \
 })
 #define rcu_dereference_raw(p) \
@@ -382,6 +382,7 @@ static inline void rcu_preempt_sleep_check(void) { }
 #define rcu_assign_pointer(p, v)					      \
 ({									      \
 	uintptr_t _r_a_p__v = (uintptr_t)(v);				      \
+	rcu_check_sparse(p, __rcu);				      \
 									      \
 	if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL)	      \
 		WRITE_ONCE((p), (typeof(p))(_r_a_p__v));		      \
@@ -785,7 +786,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
  */
 #define RCU_INIT_POINTER(p, v) \
 	do { \
-		rcu_dereference_sparse(p, __rcu); \
+		rcu_check_sparse(p, __rcu); \
 		WRITE_ONCE(p, RCU_INITIALIZER(v)); \
 	} while (0)
 
-- 
2.17.1

[PATCH tip/core/rcu 8/8] time: Move CONTEXT_TRACKING to kernel/time/Kconfig

[Paul E. McKenney]

Both CONTEXT_TRACKING and CONTEXT_TRACKING_FORCE are currently defined
in kernel/rcu/kconfig, which might have made sense at some point, but
no longer does given that RCU refers to neither of these Kconfig options.
This commit therefore moves them to kernel/time/Kconfig, where the rest
of the NO_HZ_FULL Kconfig options live.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
---
 kernel/rcu/Kconfig  | 30 ------------------------------
 kernel/time/Kconfig | 29 +++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 30 deletions(-)

diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index 939a2056c87a..37301430970e 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -87,36 +87,6 @@ config RCU_STALL_COMMON
 config RCU_NEED_SEGCBLIST
 	def_bool ( TREE_RCU || PREEMPT_RCU || TREE_SRCU )
 
-config CONTEXT_TRACKING
-       bool
-
-config CONTEXT_TRACKING_FORCE
-	bool "Force context tracking"
-	depends on CONTEXT_TRACKING
-	default y if !NO_HZ_FULL
-	help
-	  The major pre-requirement for full dynticks to work is to
-	  support the context tracking subsystem. But there are also
-	  other dependencies to provide in order to make the full
-	  dynticks working.
-
-	  This option stands for testing when an arch implements the
-	  context tracking backend but doesn't yet fullfill all the
-	  requirements to make the full dynticks feature working.
-	  Without the full dynticks, there is no way to test the support
-	  for context tracking and the subsystems that rely on it: RCU
-	  userspace extended quiescent state and tickless cputime
-	  accounting. This option copes with the absence of the full
-	  dynticks subsystem by forcing the context tracking on all
-	  CPUs in the system.
-
-	  Say Y only if you're working on the development of an
-	  architecture backend for the context tracking.
-
-	  Say N otherwise, this option brings an overhead that you
-	  don't want in production.
-
-
 config RCU_FANOUT
 	int "Tree-based hierarchical RCU fanout value"
 	range 2 64 if 64BIT
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 58b981f4bb5d..e2c038d6c13c 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -117,6 +117,35 @@ config NO_HZ_FULL
 
 endchoice
 
+config CONTEXT_TRACKING
+       bool
+
+config CONTEXT_TRACKING_FORCE
+	bool "Force context tracking"
+	depends on CONTEXT_TRACKING
+	default y if !NO_HZ_FULL
+	help
+	  The major pre-requirement for full dynticks to work is to
+	  support the context tracking subsystem. But there are also
+	  other dependencies to provide in order to make the full
+	  dynticks working.
+
+	  This option stands for testing when an arch implements the
+	  context tracking backend but doesn't yet fullfill all the
+	  requirements to make the full dynticks feature working.
+	  Without the full dynticks, there is no way to test the support
+	  for context tracking and the subsystems that rely on it: RCU
+	  userspace extended quiescent state and tickless cputime
+	  accounting. This option copes with the absence of the full
+	  dynticks subsystem by forcing the context tracking on all
+	  CPUs in the system.
+
+	  Say Y only if you're working on the development of an
+	  architecture backend for the context tracking.
+
+	  Say N otherwise, this option brings an overhead that you
+	  don't want in production.
+
 config NO_HZ
 	bool "Old Idle dynticks config"
 	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
-- 
2.17.1