Merge branches 'doc.2014.07.08a', 'fixes.2014.07.09a', 'maintainers.2…

…014.07.08b', 'nocbs.2014.07.07a' and 'torture.2014.07.07a' into HEAD

doc.2014.07.08a: Documentation updates.
fixes.2014.07.09a: Miscellaneous fixes.
maintainers.2014.07.08b: Maintainership updates.
nocbs.2014.07.07a: Callback-offloading fixes.
torture.2014.07.07a: Torture-test updates.

Documentation/kernel-parameters.txt

@@ -2802,6 +2802,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			quiescent states.  Units are jiffies, minimum
 			value is one, and maximum value is HZ.
 
+	rcutree.rcu_nocb_leader_stride= [KNL]
+			Set the number of NOCB kthread groups, which
+			defaults to the square root of the number of
+			CPUs.  Larger numbers reduces the wakeup overhead
+			on the per-CPU grace-period kthreads, but increases
+			that same overhead on each group's leader.
+
 	rcutree.qhimark= [KNL]
 			Set threshold of queued RCU callbacks beyond which
 			batch limiting is disabled.

MAINTAINERS

@@ -70,6 +70,8 @@ Descriptions of section entries:
 
 	P: Person (obsolete)
 	M: Mail patches to: FullName <address@domain>
+	R: Designated reviewer: FullName <address@domain>
+	   These reviewers should be CCed on patches.
 	L: Mailing list that is relevant to this area
 	W: Web-page with status/info
 	Q: Patchwork web based patch tracking system site
@@ -7399,10 +7401,14 @@ L:	[email protected]
 S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
 F:	Documentation/RCU/torture.txt
-F:	kernel/rcu/torture.c
+F:	kernel/rcu/rcutorture.c
 
 RCUTORTURE TEST FRAMEWORK
 M:	"Paul E. McKenney" <[email protected]>
+M:	Josh Triplett <[email protected]>
+R:	Steven Rostedt <[email protected]>
+R:	Mathieu Desnoyers <[email protected]>
+R:	Lai Jiangshan <[email protected]>
 L:	[email protected]
 S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
@@ -7425,8 +7431,11 @@ S:	Supported
 F:	net/rds/
 
 READ-COPY UPDATE (RCU)
-M:	Dipankar Sarma <[email protected]>
 M:	"Paul E. McKenney" <[email protected]>
+M:	Josh Triplett <[email protected]>
+R:	Steven Rostedt <[email protected]>
+R:	Mathieu Desnoyers <[email protected]>
+R:	Lai Jiangshan <[email protected]>
 L:	[email protected]
 W:	http://www.rdrop.com/users/paulmck/RCU/
 S:	Supported
@@ -7436,7 +7445,7 @@ X:	Documentation/RCU/torture.txt
 F:	include/linux/rcu*
 X:	include/linux/srcu.h
 F:	kernel/rcu/
-X:	kernel/rcu/torture.c
+X:	kernel/torture.c
 
 REAL TIME CLOCK (RTC) SUBSYSTEM
 M:	Alessandro Zummo <[email protected]>
@@ -8206,6 +8215,9 @@ F:	mm/sl?b.c
 SLEEPABLE READ-COPY UPDATE (SRCU)
 M:	Lai Jiangshan <[email protected]>
 M:	"Paul E. McKenney" <[email protected]>
+M:	Josh Triplett <[email protected]>
+R:	Steven Rostedt <[email protected]>
+R:	Mathieu Desnoyers <[email protected]>
 L:	[email protected]
 W:	http://www.rdrop.com/users/paulmck/RCU/
 S:	Supported

include/linux/init_task.h

@@ -102,12 +102,6 @@ extern struct group_info init_groups;
 #define INIT_IDS
 #endif
 
-#ifdef CONFIG_RCU_BOOST
-#define INIT_TASK_RCU_BOOST()						\
-	.rcu_boost_mutex = NULL,
-#else
-#define INIT_TASK_RCU_BOOST()
-#endif
 #ifdef CONFIG_TREE_PREEMPT_RCU
 #define INIT_TASK_RCU_TREE_PREEMPT()					\
 	.rcu_blocked_node = NULL,
@@ -119,8 +113,7 @@ extern struct group_info init_groups;
 	.rcu_read_lock_nesting = 0,					\
 	.rcu_read_unlock_special = 0,					\
 	.rcu_node_entry = LIST_HEAD_INIT(tsk.rcu_node_entry),		\
-	INIT_TASK_RCU_TREE_PREEMPT()					\
-	INIT_TASK_RCU_BOOST()
+	INIT_TASK_RCU_TREE_PREEMPT()
 #else
 #define INIT_TASK_RCU_PREEMPT(tsk)
 #endif

include/linux/rcupdate.h

@@ -826,15 +826,14 @@ static inline void rcu_preempt_sleep_check(void)
  * read-side critical section that would block in a !PREEMPT kernel.
  * But if you want the full story, read on!
  *
- * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it
- * is illegal to block while in an RCU read-side critical section.  In
- * preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU)
- * in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may
- * be preempted, but explicit blocking is illegal.  Finally, in preemptible
- * RCU implementations in real-time (with -rt patchset) kernel builds,
- * RCU read-side critical sections may be preempted and they may also
- * block, but only when acquiring spinlocks that are subject to priority
- * inheritance.
+ * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
+ * it is illegal to block while in an RCU read-side critical section.
+ * In preemptible RCU implementations (TREE_PREEMPT_RCU) in CONFIG_PREEMPT
+ * kernel builds, RCU read-side critical sections may be preempted,
+ * but explicit blocking is illegal.  Finally, in preemptible RCU
+ * implementations in real-time (with -rt patchset) kernel builds, RCU
+ * read-side critical sections may be preempted and they may also block, but
+ * only when acquiring spinlocks that are subject to priority inheritance.
  */
 static inline void rcu_read_lock(void)
 {
@@ -858,6 +857,34 @@ static inline void rcu_read_lock(void)
 /**
  * rcu_read_unlock() - marks the end of an RCU read-side critical section.
  *
+ * In most situations, rcu_read_unlock() is immune from deadlock.
+ * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
+ * is responsible for deboosting, which it does via rt_mutex_unlock().
+ * Unfortunately, this function acquires the scheduler's runqueue and
+ * priority-inheritance spinlocks.  This means that deadlock could result
+ * if the caller of rcu_read_unlock() already holds one of these locks or
+ * any lock that is ever acquired while holding them.
+ *
+ * That said, RCU readers are never priority boosted unless they were
+ * preempted.  Therefore, one way to avoid deadlock is to make sure
+ * that preemption never happens within any RCU read-side critical
+ * section whose outermost rcu_read_unlock() is called with one of
+ * rt_mutex_unlock()'s locks held.  Such preemption can be avoided in
+ * a number of ways, for example, by invoking preempt_disable() before
+ * critical section's outermost rcu_read_lock().
+ *
+ * Given that the set of locks acquired by rt_mutex_unlock() might change
+ * at any time, a somewhat more future-proofed approach is to make sure
+ * that that preemption never happens within any RCU read-side critical
+ * section whose outermost rcu_read_unlock() is called with irqs disabled.
+ * This approach relies on the fact that rt_mutex_unlock() currently only
+ * acquires irq-disabled locks.
+ *
+ * The second of these two approaches is best in most situations,
+ * however, the first approach can also be useful, at least to those
+ * developers willing to keep abreast of the set of locks acquired by
+ * rt_mutex_unlock().
+ *
  * See rcu_read_lock() for more information.
  */
 static inline void rcu_read_unlock(void)

include/linux/sched.h

@@ -1270,9 +1270,6 @@ struct task_struct {
 #ifdef CONFIG_TREE_PREEMPT_RCU
 	struct rcu_node *rcu_blocked_node;
 #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
-#ifdef CONFIG_RCU_BOOST
-	struct rt_mutex *rcu_boost_mutex;
-#endif /* #ifdef CONFIG_RCU_BOOST */
 
 #if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
 	struct sched_info sched_info;
@@ -2009,9 +2006,6 @@ static inline void rcu_copy_process(struct task_struct *p)
 #ifdef CONFIG_TREE_PREEMPT_RCU
 	p->rcu_blocked_node = NULL;
 #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
-#ifdef CONFIG_RCU_BOOST
-	p->rcu_boost_mutex = NULL;
-#endif /* #ifdef CONFIG_RCU_BOOST */
 	INIT_LIST_HEAD(&p->rcu_node_entry);
 }
 

include/linux/tick.h

@@ -12,6 +12,7 @@
 #include <linux/hrtimer.h>
 #include <linux/context_tracking_state.h>
 #include <linux/cpumask.h>
+#include <linux/sched.h>
 
 #ifdef CONFIG_GENERIC_CLOCKEVENTS
 
@@ -162,6 +163,7 @@ static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
 #ifdef CONFIG_NO_HZ_FULL
 extern bool tick_nohz_full_running;
 extern cpumask_var_t tick_nohz_full_mask;
+extern cpumask_var_t housekeeping_mask;
 
 static inline bool tick_nohz_full_enabled(void)
 {
@@ -194,6 +196,24 @@ static inline void tick_nohz_full_kick_all(void) { }
 static inline void __tick_nohz_task_switch(struct task_struct *tsk) { }
 #endif
 
+static inline bool is_housekeeping_cpu(int cpu)
+{
+#ifdef CONFIG_NO_HZ_FULL
+	if (tick_nohz_full_enabled())
+		return cpumask_test_cpu(cpu, housekeeping_mask);
+#endif
+	return true;
+}
+
+static inline void housekeeping_affine(struct task_struct *t)
+{
+#ifdef CONFIG_NO_HZ_FULL
+	if (tick_nohz_full_enabled())
+		set_cpus_allowed_ptr(t, housekeeping_mask);
+
+#endif
+}
+
 static inline void tick_nohz_full_check(void)
 {
 	if (tick_nohz_full_enabled())

init/Kconfig

@@ -505,7 +505,7 @@ config PREEMPT_RCU
 	def_bool TREE_PREEMPT_RCU
 	help
 	  This option enables preemptible-RCU code that is common between
-	  the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
+	  TREE_PREEMPT_RCU and, in the old days, TINY_PREEMPT_RCU.
 
 config RCU_STALL_COMMON
 	def_bool ( TREE_RCU || TREE_PREEMPT_RCU || RCU_TRACE )
@@ -737,7 +737,7 @@ choice
 
 config RCU_NOCB_CPU_NONE
 	bool "No build_forced no-CBs CPUs"
-	depends on RCU_NOCB_CPU && !NO_HZ_FULL
+	depends on RCU_NOCB_CPU && !NO_HZ_FULL_ALL
 	help
 	  This option does not force any of the CPUs to be no-CBs CPUs.
 	  Only CPUs designated by the rcu_nocbs= boot parameter will be
@@ -751,7 +751,7 @@ config RCU_NOCB_CPU_NONE
 
 config RCU_NOCB_CPU_ZERO
 	bool "CPU 0 is a build_forced no-CBs CPU"
-	depends on RCU_NOCB_CPU && !NO_HZ_FULL
+	depends on RCU_NOCB_CPU && !NO_HZ_FULL_ALL
 	help
 	  This option forces CPU 0 to be a no-CBs CPU, so that its RCU
 	  callbacks are invoked by a per-CPU kthread whose name begins

kernel/rcu/rcu.h

@@ -99,6 +99,10 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head)
 
 void kfree(const void *);
 
+/*
+ * Reclaim the specified callback, either by invoking it (non-lazy case)
+ * or freeing it directly (lazy case).  Return true if lazy, false otherwise.
+ */
 static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
 {
 	unsigned long offset = (unsigned long)head->func;
@@ -108,12 +112,12 @@ static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
 		RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset));
 		kfree((void *)head - offset);
 		rcu_lock_release(&rcu_callback_map);
-		return 1;
+		return true;
 	} else {
 		RCU_TRACE(trace_rcu_invoke_callback(rn, head));
 		head->func(head);
 		rcu_lock_release(&rcu_callback_map);
-		return 0;
+		return false;
 	}
 }
 

kernel/rcu/srcu.c

@@ -298,9 +298,9 @@ int __srcu_read_lock(struct srcu_struct *sp)
 
 	idx = ACCESS_ONCE(sp->completed) & 0x1;
 	preempt_disable();
-	ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1;
+	__this_cpu_inc(sp->per_cpu_ref->c[idx]);
 	smp_mb(); /* B */  /* Avoid leaking the critical section. */
-	ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1;
+	__this_cpu_inc(sp->per_cpu_ref->seq[idx]);
 	preempt_enable();
 	return idx;
 }