Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu

Pull RCU changes from Paul E. McKenney:

 - Adding transitivity uniformly to rcu_node structure ->lock
   acquisitions.  (This is implemented by the first two commits
   on top of v4.4-rc2 due to the pervasive nature of this change.)

 - Documentation updates, including RCU requirements.

 - Expedited grace-period changes.

 - Miscellaneous fixes.

 - Linked-list fixes, courtesy of KTSAN.

 - Torture-test updates.

 - Late-breaking fix to sysrq-generated crash.

Signed-off-by: Ingo Molnar <mingo@kernel.org>

8 files changed, 124 insertions, 36 deletions

diff --git a/include/linux/list.h b/include/linux/list.h
index 993395a2e55c..5356f4d661a7 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -24,7 +24,7 @@
 
 static inline void INIT_LIST_HEAD(struct list_head *list)
 {
-	list->next = list;
+	WRITE_ONCE(list->next, list);
 	list->prev = list;
 }
 
@@ -42,7 +42,7 @@ static inline void __list_add(struct list_head *new,
 	next->prev = new;
 	new->next = next;
 	new->prev = prev;
-	prev->next = new;
+	WRITE_ONCE(prev->next, new);
 }
 #else
 extern void __list_add(struct list_head *new,
@@ -186,7 +186,7 @@ static inline int list_is_last(const struct list_head *list,
  */
 static inline int list_empty(const struct list_head *head)
 {
-	return head->next == head;
+	return READ_ONCE(head->next) == head;
 }
 
 /**
@@ -608,7 +608,7 @@ static inline int hlist_unhashed(const struct hlist_node *h)
 
 static inline int hlist_empty(const struct hlist_head *h)
 {
-	return !h->first;
+	return !READ_ONCE(h->first);
 }
 
 static inline void __hlist_del(struct hlist_node *n)
@@ -642,7 +642,7 @@ static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
 	n->next = first;
 	if (first)
 		first->pprev = &n->next;
-	h->first = n;
+	WRITE_ONCE(h->first, n);
 	n->pprev = &h->first;
 }
 
@@ -653,14 +653,14 @@ static inline void hlist_add_before(struct hlist_node *n,
 	n->pprev = next->pprev;
 	n->next = next;
 	next->pprev = &n->next;
-	*(n->pprev) = n;
+	WRITE_ONCE(*(n->pprev), n);
 }
 
 static inline void hlist_add_behind(struct hlist_node *n,
 				    struct hlist_node *prev)
 {
 	n->next = prev->next;
-	prev->next = n;
+	WRITE_ONCE(prev->next, n);
 	n->pprev = &prev->next;
 
 	if (n->next)
diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
index 8132214e8efd..ee7229a6c06a 100644
--- a/include/linux/list_bl.h
+++ b/include/linux/list_bl.h
@@ -70,7 +70,7 @@ static inline void hlist_bl_set_first(struct hlist_bl_head *h,
 
 static inline int hlist_bl_empty(const struct hlist_bl_head *h)
 {
-	return !((unsigned long)h->first & ~LIST_BL_LOCKMASK);
+	return !((unsigned long)READ_ONCE(h->first) & ~LIST_BL_LOCKMASK);
 }
 
 static inline void hlist_bl_add_head(struct hlist_bl_node *n,
diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
index 444d2b1313bd..b01fe1009084 100644
--- a/include/linux/list_nulls.h
+++ b/include/linux/list_nulls.h
@@ -57,7 +57,7 @@ static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
 
 static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
 {
-	return is_a_nulls(h->first);
+	return is_a_nulls(READ_ONCE(h->first));
 }
 
 static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 5ed540986019..14ec1652daf4 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -179,32 +179,31 @@ static inline void list_replace_rcu(struct list_head *old,
 }
 
 /**
- * list_splice_init_rcu - splice an RCU-protected list into an existing list.
+ * __list_splice_init_rcu - join an RCU-protected list into an existing list.
  * @list:	the RCU-protected list to splice
- * @head:	the place in the list to splice the first list into
+ * @prev:	points to the last element of the existing list
+ * @next:	points to the first element of the existing list
  * @sync:	function to sync: synchronize_rcu(), synchronize_sched(), ...
  *
- * @head can be RCU-read traversed concurrently with this function.
+ * The list pointed to by @prev and @next can be RCU-read traversed
+ * concurrently with this function.
  *
  * Note that this function blocks.
  *
- * Important note: the caller must take whatever action is necessary to
- *	prevent any other updates to @head.  In principle, it is possible
- *	to modify the list as soon as sync() begins execution.
- *	If this sort of thing becomes necessary, an alternative version
- *	based on call_rcu() could be created.  But only if -really-
- *	needed -- there is no shortage of RCU API members.
+ * Important note: the caller must take whatever action is necessary to prevent
+ * any other updates to the existing list.  In principle, it is possible to
+ * modify the list as soon as sync() begins execution. If this sort of thing
+ * becomes necessary, an alternative version based on call_rcu() could be
+ * created.  But only if -really- needed -- there is no shortage of RCU API
+ * members.
  */
-static inline void list_splice_init_rcu(struct list_head *list,
-					struct list_head *head,
-					void (*sync)(void))
+static inline void __list_splice_init_rcu(struct list_head *list,
+					  struct list_head *prev,
+					  struct list_head *next,
+					  void (*sync)(void))
 {
 	struct list_head *first = list->next;
 	struct list_head *last = list->prev;
-	struct list_head *at = head->next;
-
-	if (list_empty(list))
-		return;
 
 	/*
 	 * "first" and "last" tracking list, so initialize it.  RCU readers
@@ -231,10 +230,40 @@ static inline void list_splice_init_rcu(struct list_head *list,
 	 * this function.
 	 */
 
-	last->next = at;
-	rcu_assign_pointer(list_next_rcu(head), first);
-	first->prev = head;
-	at->prev = last;
+	last->next = next;
+	rcu_assign_pointer(list_next_rcu(prev), first);
+	first->prev = prev;
+	next->prev = last;
+}
+
+/**
+ * list_splice_init_rcu - splice an RCU-protected list into an existing list,
+ *                        designed for stacks.
+ * @list:	the RCU-protected list to splice
+ * @head:	the place in the existing list to splice the first list into
+ * @sync:	function to sync: synchronize_rcu(), synchronize_sched(), ...
+ */
+static inline void list_splice_init_rcu(struct list_head *list,
+					struct list_head *head,
+					void (*sync)(void))
+{
+	if (!list_empty(list))
+		__list_splice_init_rcu(list, head, head->next, sync);
+}
+
+/**
+ * list_splice_tail_init_rcu - splice an RCU-protected list into an existing
+ *                             list, designed for queues.
+ * @list:	the RCU-protected list to splice
+ * @head:	the place in the existing list to splice the first list into
+ * @sync:	function to sync: synchronize_rcu(), synchronize_sched(), ...
+ */
+static inline void list_splice_tail_init_rcu(struct list_head *list,
+					     struct list_head *head,
+					     void (*sync)(void))
+{
+	if (!list_empty(list))
+		__list_splice_init_rcu(list, head->prev, head, sync);
 }
 
 /**
@@ -305,6 +334,42 @@ static inline void list_splice_init_rcu(struct list_head *list,
 		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
 
 /**
+ * list_entry_lockless - get the struct for this entry
+ * @ptr:        the &struct list_head pointer.
+ * @type:       the type of the struct this is embedded in.
+ * @member:     the name of the list_head within the struct.
+ *
+ * This primitive may safely run concurrently with the _rcu list-mutation
+ * primitives such as list_add_rcu(), but requires some implicit RCU
+ * read-side guarding.  One example is running within a special
+ * exception-time environment where preemption is disabled and where
+ * lockdep cannot be invoked (in which case updaters must use RCU-sched,
+ * as in synchronize_sched(), call_rcu_sched(), and friends).  Another
+ * example is when items are added to the list, but never deleted.
+ */
+#define list_entry_lockless(ptr, type, member) \
+	container_of((typeof(ptr))lockless_dereference(ptr), type, member)
+
+/**
+ * list_for_each_entry_lockless - iterate over rcu list of given type
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_struct within the struct.
+ *
+ * This primitive may safely run concurrently with the _rcu list-mutation
+ * primitives such as list_add_rcu(), but requires some implicit RCU
+ * read-side guarding.  One example is running within a special
+ * exception-time environment where preemption is disabled and where
+ * lockdep cannot be invoked (in which case updaters must use RCU-sched,
+ * as in synchronize_sched(), call_rcu_sched(), and friends).  Another
+ * example is when items are added to the list, but never deleted.
+ */
+#define list_for_each_entry_lockless(pos, head, member) \
+	for (pos = list_entry_lockless((head)->next, typeof(*pos), member); \
+	     &pos->member != (head); \
+	     pos = list_entry_lockless(pos->member.next, typeof(*pos), member))
+
+/**
  * list_for_each_entry_continue_rcu - continue iteration over list of given type
  * @pos:	the type * to use as a loop cursor.
  * @head:	the head for your list.
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index a0189ba67fde..14e6f47ee16f 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -48,10 +48,17 @@
 
 #include <asm/barrier.h>
 
+#ifndef CONFIG_TINY_RCU
 extern int rcu_expedited; /* for sysctl */
+extern int rcu_normal;    /* also for sysctl */
+#endif /* #ifndef CONFIG_TINY_RCU */
 
 #ifdef CONFIG_TINY_RCU
 /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
+static inline bool rcu_gp_is_normal(void)  /* Internal RCU use. */
+{
+	return true;
+}
 static inline bool rcu_gp_is_expedited(void)  /* Internal RCU use. */
 {
 	return false;
@@ -65,6 +72,7 @@ static inline void rcu_unexpedite_gp(void)
 {
 }
 #else /* #ifdef CONFIG_TINY_RCU */
+bool rcu_gp_is_normal(void);     /* Internal RCU use. */
 bool rcu_gp_is_expedited(void);  /* Internal RCU use. */
 void rcu_expedite_gp(void);
 void rcu_unexpedite_gp(void);
@@ -321,7 +329,6 @@ static inline int rcu_preempt_depth(void)
 
 /* Internal to kernel */
 void rcu_init(void);
-void rcu_end_inkernel_boot(void);
 void rcu_sched_qs(void);
 void rcu_bh_qs(void);
 void rcu_check_callbacks(int user);
@@ -329,6 +336,12 @@ struct notifier_block;
 int rcu_cpu_notify(struct notifier_block *self,
 		   unsigned long action, void *hcpu);
 
+#ifndef CONFIG_TINY_RCU
+void rcu_end_inkernel_boot(void);
+#else /* #ifndef CONFIG_TINY_RCU */
+static inline void rcu_end_inkernel_boot(void) { }
+#endif /* #ifndef CONFIG_TINY_RCU */
+
 #ifdef CONFIG_RCU_STALL_COMMON
 void rcu_sysrq_start(void);
 void rcu_sysrq_end(void);
@@ -379,9 +392,9 @@ static inline void rcu_init_nohz(void)
  */
 #define RCU_NONIDLE(a) \
 	do { \
-		rcu_irq_enter(); \
+		rcu_irq_enter_irqson(); \
 		do { a; } while (0); \
-		rcu_irq_exit(); \
+		rcu_irq_exit_irqson(); \
 	} while (0)
 
 /*
@@ -741,7 +754,7 @@ static inline void rcu_preempt_sleep_check(void)
  * The tracing infrastructure traces RCU (we want that), but unfortunately
  * some of the RCU checks causes tracing to lock up the system.
  *
- * The tracing version of rcu_dereference_raw() must not call
+ * The no-tracing version of rcu_dereference_raw() must not call
  * rcu_read_lock_held().
  */
 #define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 4c1aaf9cce7b..64809aea661c 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -181,6 +181,14 @@ static inline void rcu_irq_enter(void)
 {
 }
 
+static inline void rcu_irq_exit_irqson(void)
+{
+}
+
+static inline void rcu_irq_enter_irqson(void)
+{
+}
+
 static inline void rcu_irq_exit(void)
 {
 }
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 60d15a080d7c..ad1eda9fa4da 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -37,7 +37,7 @@ void rcu_cpu_stall_reset(void);
 /*
  * Note a virtualization-based context switch.  This is simply a
  * wrapper around rcu_note_context_switch(), which allows TINY_RCU
- * to save a few bytes.
+ * to save a few bytes. The caller must have disabled interrupts.
  */
 static inline void rcu_virt_note_context_switch(int cpu)
 {
@@ -97,6 +97,8 @@ void rcu_idle_enter(void);
 void rcu_idle_exit(void);
 void rcu_irq_enter(void);
 void rcu_irq_exit(void);
+void rcu_irq_enter_irqson(void);
+void rcu_irq_exit_irqson(void);
 
 void exit_rcu(void);
 
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 696a339c592c..7834a8a8bf1e 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -171,8 +171,8 @@ extern void syscall_unregfunc(void);
 				TP_PROTO(data_proto),			\
 				TP_ARGS(data_args),			\
 				TP_CONDITION(cond),			\
-				rcu_irq_enter(),			\
-				rcu_irq_exit());			\
+				rcu_irq_enter_irqson(),			\
+				rcu_irq_exit_irqson());			\
 	}
 #else
 #define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args)