[PATCH tip/core/rcu 0/7] Yet more RCU commits queued for 2.6.37

[PATCH tip/core/rcu 0/7] Yet more RCU commits queued for 2.6.37

[Paul E. McKenney]

Hello!

This patchset shows additional patches queued for 2.6.37, over
and above those posted at http://lkml.org/lkml/2010/7/14/334 and
at http://lkml.org/lkml/2010/8/9/332.  These are all trivial fixes.
The patches are as follows:

1.	Allow kernel debuggers to avoid spurious RCU CPU stall warnings
	when restarting from a breakpoint via a new rcu_cpu_stall_reset().
2.	Repair code-duplication FIXMEs.  This code was temporarily
	duplicated to avoid inter-patch dependencies in the RCU tree.
3.	Document some additional ways of stalling updates to prevent
	call_rcu()-induced OOM situations.
4.	Update srcu_read_lock() docbook comment to note that it is
	illegal to wait for a given flavor of SRCU grace period while
	in that same flavor of SRCU read-side critical section.
5.	Combine duplicate code, courtesy of a newly refurbished
	CONFIG_PREEMPT_RCU symbol.  Also convert from macro to
	static inline function in a couple of places.
6.	Apply the TINY_PREEMPT_RCU read-side speedups/fixes to
	TREE_PREEMPT_RCU.  This update to TINY_PREEMPT_RCU update was
	posted at http://lkml.org/lkml/2010/8/17/437.
7.	Add a comment stating that list_empty() serves the function of
	the non-existent list_empty_rcu().

For a testing-only version of this patchset from git, please see:

git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git rcu/testing

							Thanx, Paul

 b/Documentation/RCU/checklist.txt |   23 ++++++++---
 b/include/linux/rculist.h         |    9 ++++
 b/include/linux/rcupdate.h        |   15 +++++++
 b/include/linux/rcutiny.h         |    4 ++
 b/include/linux/rcutree.h         |    1 
 b/include/linux/srcu.h            |    7 +++
 b/kernel/rcutiny_plugin.h         |    4 --
 b/kernel/rcutree.c                |   20 ++++++++++
 b/kernel/rcutree.h                |    1 
 b/kernel/rcutree_plugin.h         |   18 +++++++++
 include/linux/rcupdate.h          |   75 ++++++++++++++++++++++++++++++++++++--
 include/linux/rcutiny.h           |   58 -----------------------------
 include/linux/rcutree.h           |   56 ----------------------------
 kernel/rcutree.h                  |    3 -
 kernel/rcutree_plugin.h           |   15 ++-----
 15 files changed, 166 insertions(+), 143 deletions(-)

[PATCH tip/core/rcu 1/7] rcu: permit suppressing current grace period's CPU stall warnings

[Paul E. McKenney]

When using a kernel debugger, a long sojourn in the debugger can get
you lots of RCU CPU stall warnings once you resume.  This might not be
helpful, especially if you are using the system console.  This patch
therefore allows RCU CPU stall warnings to be suppressed, but only for
the duration of the current set of grace periods.

This differs from Jason's original patch in that it adds support for
tiny RCU and preemptible RCU, and uses a slightly different method for
suppressing the RCU CPU stall warning messages.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Jason Wessel <jason.wessel@windriver.com>
---
 include/linux/rcutiny.h |    4 ++++
 include/linux/rcutree.h |    1 +
 kernel/rcutree.c        |   20 ++++++++++++++++++++
 kernel/rcutree.h        |    1 +
 kernel/rcutree_plugin.h |   18 ++++++++++++++++++
 5 files changed, 44 insertions(+), 0 deletions(-)

diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 4cc5eba..3fa1797 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -178,6 +178,10 @@ static inline void rcu_sched_force_quiescent_state(void)
 {
 }
 
+static inline void rcu_cpu_stall_reset(void)
+{
+}
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
 extern int rcu_scheduler_active __read_mostly;
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index c13b85d..0726809 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -36,6 +36,7 @@ extern void rcu_sched_qs(int cpu);
 extern void rcu_bh_qs(int cpu);
 extern void rcu_note_context_switch(int cpu);
 extern int rcu_needs_cpu(int cpu);
+extern void rcu_cpu_stall_reset(void);
 
 #ifdef CONFIG_TREE_PREEMPT_RCU
 
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index ff21411..42140a8 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -565,6 +565,22 @@ static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
 	return NOTIFY_DONE;
 }
 
+/**
+ * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
+ *
+ * Set the stall-warning timeout way off into the future, thus preventing
+ * any RCU CPU stall-warning messages from appearing in the current set of
+ * RCU grace periods.
+ *
+ * The caller must disable hard irqs.
+ */
+void rcu_cpu_stall_reset(void)
+{
+	rcu_sched_state.jiffies_stall = jiffies + ULONG_MAX / 2;
+	rcu_bh_state.jiffies_stall = jiffies + ULONG_MAX / 2;
+	rcu_preempt_stall_reset();
+}
+
 static struct notifier_block rcu_panic_block = {
 	.notifier_call = rcu_panic,
 };
@@ -584,6 +600,10 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
 {
 }
 
+void rcu_cpu_stall_reset(void)
+{
+}
+
 static void __init check_cpu_stall_init(void)
 {
 }
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index bb4d086..7abd439 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -372,6 +372,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
 static void rcu_print_detail_task_stall(struct rcu_state *rsp);
 static void rcu_print_task_stall(struct rcu_node *rnp);
+static void rcu_preempt_stall_reset(void);
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
 #ifdef CONFIG_HOTPLUG_CPU
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 63bb771..561410f 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -417,6 +417,16 @@ static void rcu_print_task_stall(struct rcu_node *rnp)
 	}
 }
 
+/*
+ * Suppress preemptible RCU's CPU stall warnings by pushing the
+ * time of the next stall-warning message comfortably far into the
+ * future.
+ */
+static void rcu_preempt_stall_reset(void)
+{
+	rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2;
+}
+
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 
 /*
@@ -867,6 +877,14 @@ static void rcu_print_task_stall(struct rcu_node *rnp)
 {
 }
 
+/*
+ * Because preemptible RCU does not exist, there is no need to suppress
+ * its CPU stall warnings.
+ */
+static void rcu_preempt_stall_reset(void)
+{
+}
+
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 
 /*
-- 
1.7.0.6

[PATCH tip/core/rcu 2/7] rcu: repair code-duplication FIXMEs

[Paul E. McKenney]

Combine the duplicate definitions of ULONG_CMP_GE(), ULONG_CMP_LT(),
and rcu_preempt_depth() into include/linux/rcupdate.h.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h |   15 +++++++++++++++
 include/linux/rcutiny.h  |    7 -------
 include/linux/rcutree.h  |    6 ------
 kernel/rcutiny_plugin.h  |    4 ----
 kernel/rcutree.h         |    3 ---
 5 files changed, 15 insertions(+), 20 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index d7af96e..325bad7 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -47,6 +47,9 @@
 extern int rcutorture_runnable; /* for sysctl */
 #endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
 
+#define ULONG_CMP_GE(a, b)	(ULONG_MAX / 2 >= (a) - (b))
+#define ULONG_CMP_LT(a, b)	(ULONG_MAX / 2 < (a) - (b))
+
 /**
  * struct rcu_head - callback structure for use with RCU
  * @next: next update requests in a list
@@ -66,6 +69,18 @@ extern int sched_expedited_torture_stats(char *page);
 /* Internal to kernel */
 extern void rcu_init(void);
 
+#ifdef CONFIG_PREEMPT_RCU
+
+/*
+ * Defined as a macro as it is a very low level header included from
+ * areas that don't even know about current.  This gives the rcu_read_lock()
+ * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
+ * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
+ */
+#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
+
+#endif /* #ifdef CONFIG_PREEMPT_RCU */
+
 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
 #include <linux/rcutree.h>
 #elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 3fa1797..c6b11dc 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -133,13 +133,6 @@ static inline int rcu_needs_cpu(int cpu)
 	return rcu_preempt_needs_cpu();
 }
 
-/*
- * Defined as macro as it is a very low level header
- * included from areas that don't even know about current
- * FIXME: combine with include/linux/rcutree.h into rcupdate.h.
- */
-#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
-
 #endif /* #else #ifdef CONFIG_TINY_RCU */
 
 static inline void rcu_note_context_switch(int cpu)
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 0726809..54a20c1 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -45,12 +45,6 @@ extern void __rcu_read_unlock(void);
 extern void synchronize_rcu(void);
 extern void exit_rcu(void);
 
-/*
- * Defined as macro as it is a very low level header
- * included from areas that don't even know about current
- */
-#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
-
 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
 
 static inline void __rcu_read_lock(void)
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index e6bc1b4..c5bea11 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -26,10 +26,6 @@
 
 #include <linux/delay.h>
 
-/* FIXME: merge with definitions in kernel/rcutree.h. */
-#define ULONG_CMP_GE(a, b)	(ULONG_MAX / 2 >= (a) - (b))
-#define ULONG_CMP_LT(a, b)	(ULONG_MAX / 2 < (a) - (b))
-
 /* Global control variables for preemptible RCU. */
 struct rcu_preempt_ctrlblk {
 	struct rcu_ctrlblk rcb;	/* curtail: ->next ptr of last CB for GP. */
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 7abd439..7918ba6 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -272,9 +272,6 @@ struct rcu_data {
 
 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
 
-#define ULONG_CMP_GE(a, b)	(ULONG_MAX / 2 >= (a) - (b))
-#define ULONG_CMP_LT(a, b)	(ULONG_MAX / 2 < (a) - (b))
-
 /*
  * RCU global state, including node hierarchy.  This hierarchy is
  * represented in "heap" form in a dense array.  The root (first level)
-- 
1.7.0.6

[PATCH tip/core/rcu 3/7] rcu: document ways of stalling updates in low-memory situations

[Paul E. McKenney]

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 Documentation/RCU/checklist.txt |   23 ++++++++++++++++-------
 1 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index c7c6788..0c134f8 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -218,13 +218,22 @@ over a rather long period of time, but improvements are always welcome!
 	include:
 
 	a.	Keeping a count of the number of data-structure elements
-		used by the RCU-protected data structure, including those
-		waiting for a grace period to elapse.  Enforce a limit
-		on this number, stalling updates as needed to allow
-		previously deferred frees to complete.
-
-		Alternatively, limit only the number awaiting deferred
-		free rather than the total number of elements.
+		used by the RCU-protected data structure, including
+		those waiting for a grace period to elapse.  Enforce a
+		limit on this number, stalling updates as needed to allow
+		previously deferred frees to complete.	Alternatively,
+		limit only the number awaiting deferred free rather than
+		the total number of elements.
+
+		One way to stall the updates is to acquire the update-side
+		mutex.	(Don't try this with a spinlock -- other CPUs
+		spinning on the lock could prevent the grace period
+		from ever ending.)  Another way to stall the updates
+		is for the updates to use a wrapper function around
+		the memory allocator, so that this wrapper function
+		simulates OOM when there is too much memory awaiting an
+		RCU grace period.  There are of course many other
+		variations on this theme.
 
 	b.	Limiting update rate.  For example, if updates occur only
 		once per hour, then no explicit rate limiting is required,
-- 
1.7.0.6

[PATCH tip/core/rcu 4/7] rcu: Upgrade srcu_read_lock() docbook about SRCU grace periods

[Paul E. McKenney]

It is illegal to wait for an SRCU grace period while within the
corresponding flavor of SRCU read-side critical section.  Therefore,
this commit updates the srcu_read_lock() docbook accordingly.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/srcu.h |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 6f456a7..58971e8 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -139,7 +139,12 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp)
  * @sp: srcu_struct in which to register the new reader.
  *
  * Enter an SRCU read-side critical section.  Note that SRCU read-side
- * critical sections may be nested.
+ * critical sections may be nested.  However, it is illegal to
+ * call anything that waits on an SRCU grace period for the same
+ * srcu_struct, whether directly or indirectly.  Please note that
+ * one way to indirectly wait on an SRCU grace period is to acquire
+ * a mutex that is held elsewhere while calling synchronize_srcu() or
+ * synchronize_srcu_expedited().
  */
 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 {
-- 
1.7.0.6

[PATCH tip/core/rcu 5/7] rcu: combine duplicate code, courtesy of CONFIG_PREEMPT_RCU

[Paul E. McKenney]

The CONFIG_PREEMPT_RCU kernel configuration parameter was recently
re-introduced, but as an indication of the type of RCU (preemptible
vs. non-preemptible) instead of as selecting a given implementation.
This commit uses CONFIG_PREEMPT_RCU to combine duplicate code
from include/linux/rcutiny.h and include/linux/rcutree.h into
include/linux/rcupdate.h.  This commit also combines a few other pieces
of duplicate code that have accumulated.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h |   75 ++++++++++++++++++++++++++++++++++++++++++++--
 include/linux/rcutiny.h  |   51 -------------------------------
 include/linux/rcutree.h  |   50 ------------------------------
 kernel/rcutree_plugin.h  |    9 -----
 4 files changed, 72 insertions(+), 113 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 325bad7..89414d6 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -61,16 +61,30 @@ struct rcu_head {
 };
 
 /* Exported common interfaces */
+extern void call_rcu_sched(struct rcu_head *head,
+			   void (*func)(struct rcu_head *rcu));
+extern void synchronize_sched(void);
 extern void rcu_barrier_bh(void);
 extern void rcu_barrier_sched(void);
 extern void synchronize_sched_expedited(void);
 extern int sched_expedited_torture_stats(char *page);
 
-/* Internal to kernel */
-extern void rcu_init(void);
+static inline void __rcu_read_lock_bh(void)
+{
+	local_bh_disable();
+}
+
+static inline void __rcu_read_unlock_bh(void)
+{
+	local_bh_enable();
+}
 
 #ifdef CONFIG_PREEMPT_RCU
 
+extern void __rcu_read_lock(void);
+extern void __rcu_read_unlock(void);
+void synchronize_rcu(void);
+
 /*
  * Defined as a macro as it is a very low level header included from
  * areas that don't even know about current.  This gives the rcu_read_lock()
@@ -79,7 +93,53 @@ extern void rcu_init(void);
  */
 #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
 
-#endif /* #ifdef CONFIG_PREEMPT_RCU */
+#else /* #ifdef CONFIG_PREEMPT_RCU */
+
+static inline void __rcu_read_lock(void)
+{
+	preempt_disable();
+}
+
+static inline void __rcu_read_unlock(void)
+{
+	preempt_enable();
+}
+
+static inline void synchronize_rcu(void)
+{
+	synchronize_sched();
+}
+
+static inline int rcu_preempt_depth(void)
+{
+	return 0;
+}
+
+#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+
+/* Internal to kernel */
+extern void rcu_init(void);
+extern void rcu_sched_qs(int cpu);
+extern void rcu_bh_qs(int cpu);
+extern void rcu_check_callbacks(int cpu, int user);
+struct notifier_block;
+
+#ifdef CONFIG_NO_HZ
+
+extern void rcu_enter_nohz(void);
+extern void rcu_exit_nohz(void);
+
+#else /* #ifdef CONFIG_NO_HZ */
+
+static inline void rcu_enter_nohz(void)
+{
+}
+
+static inline void rcu_exit_nohz(void)
+{
+}
+
+#endif /* #else #ifdef CONFIG_NO_HZ */
 
 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
 #include <linux/rcutree.h>
@@ -626,6 +686,8 @@ struct rcu_synchronize {
 
 extern void wakeme_after_rcu(struct rcu_head  *head);
 
+#ifdef CONFIG_PREEMPT_RCU
+
 /**
  * call_rcu() - Queue an RCU callback for invocation after a grace period.
  * @head: structure to be used for queueing the RCU updates.
@@ -642,6 +704,13 @@ extern void wakeme_after_rcu(struct rcu_head  *head);
 extern void call_rcu(struct rcu_head *head,
 			      void (*func)(struct rcu_head *head));
 
+#else /* #ifdef CONFIG_PREEMPT_RCU */
+
+/* In classic RCU, call_rcu() is just call_rcu_sched(). */
+#define	call_rcu	call_rcu_sched
+
+#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+
 /**
  * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
  * @head: structure to be used for queueing the RCU updates.
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index c6b11dc..13877cb 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -27,34 +27,10 @@
 
 #include <linux/cache.h>
 
-void rcu_sched_qs(int cpu);
-void rcu_bh_qs(int cpu);
-
-#ifdef CONFIG_TINY_RCU
-#define __rcu_read_lock()	preempt_disable()
-#define __rcu_read_unlock()	preempt_enable()
-#else /* #ifdef CONFIG_TINY_RCU */
-void __rcu_read_lock(void);
-void __rcu_read_unlock(void);
-#endif /* #else #ifdef CONFIG_TINY_RCU */
-#define __rcu_read_lock_bh()	local_bh_disable()
-#define __rcu_read_unlock_bh()	local_bh_enable()
-extern void call_rcu_sched(struct rcu_head *head,
-			   void (*func)(struct rcu_head *rcu));
-
 #define rcu_init_sched()	do { } while (0)
 
-extern void synchronize_sched(void);
-
 #ifdef CONFIG_TINY_RCU
 
-#define call_rcu		call_rcu_sched
-
-static inline void synchronize_rcu(void)
-{
-	synchronize_sched();
-}
-
 static inline void synchronize_rcu_expedited(void)
 {
 	synchronize_sched();	/* Only one CPU, so pretty fast anyway!!! */
@@ -67,7 +43,6 @@ static inline void rcu_barrier(void)
 
 #else /* #ifdef CONFIG_TINY_RCU */
 
-void synchronize_rcu(void);
 void rcu_barrier(void);
 void synchronize_rcu_expedited(void);
 
@@ -83,25 +58,6 @@ static inline void synchronize_rcu_bh_expedited(void)
 	synchronize_sched();
 }
 
-struct notifier_block;
-
-#ifdef CONFIG_NO_HZ
-
-extern void rcu_enter_nohz(void);
-extern void rcu_exit_nohz(void);
-
-#else /* #ifdef CONFIG_NO_HZ */
-
-static inline void rcu_enter_nohz(void)
-{
-}
-
-static inline void rcu_exit_nohz(void)
-{
-}
-
-#endif /* #else #ifdef CONFIG_NO_HZ */
-
 #ifdef CONFIG_TINY_RCU
 
 static inline void rcu_preempt_note_context_switch(void)
@@ -117,11 +73,6 @@ static inline int rcu_needs_cpu(int cpu)
 	return 0;
 }
 
-static inline int rcu_preempt_depth(void)
-{
-	return 0;
-}
-
 #else /* #ifdef CONFIG_TINY_RCU */
 
 void rcu_preempt_note_context_switch(void);
@@ -141,8 +92,6 @@ static inline void rcu_note_context_switch(int cpu)
 	rcu_preempt_note_context_switch();
 }
 
-extern void rcu_check_callbacks(int cpu, int user);
-
 /*
  * Return the number of grace periods.
  */
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 54a20c1..95518e6 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -30,59 +30,23 @@
 #ifndef __LINUX_RCUTREE_H
 #define __LINUX_RCUTREE_H
 
-struct notifier_block;
-
-extern void rcu_sched_qs(int cpu);
-extern void rcu_bh_qs(int cpu);
 extern void rcu_note_context_switch(int cpu);
 extern int rcu_needs_cpu(int cpu);
 extern void rcu_cpu_stall_reset(void);
 
 #ifdef CONFIG_TREE_PREEMPT_RCU
 
-extern void __rcu_read_lock(void);
-extern void __rcu_read_unlock(void);
-extern void synchronize_rcu(void);
 extern void exit_rcu(void);
 
 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
 
-static inline void __rcu_read_lock(void)
-{
-	preempt_disable();
-}
-
-static inline void __rcu_read_unlock(void)
-{
-	preempt_enable();
-}
-
-#define synchronize_rcu synchronize_sched
-
 static inline void exit_rcu(void)
 {
 }
 
-static inline int rcu_preempt_depth(void)
-{
-	return 0;
-}
-
 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
 
-static inline void __rcu_read_lock_bh(void)
-{
-	local_bh_disable();
-}
-static inline void __rcu_read_unlock_bh(void)
-{
-	local_bh_enable();
-}
-
-extern void call_rcu_sched(struct rcu_head *head,
-			   void (*func)(struct rcu_head *rcu));
 extern void synchronize_rcu_bh(void);
-extern void synchronize_sched(void);
 extern void synchronize_rcu_expedited(void);
 
 static inline void synchronize_rcu_bh_expedited(void)
@@ -92,8 +56,6 @@ static inline void synchronize_rcu_bh_expedited(void)
 
 extern void rcu_barrier(void);
 
-extern void rcu_check_callbacks(int cpu, int user);
-
 extern long rcu_batches_completed(void);
 extern long rcu_batches_completed_bh(void);
 extern long rcu_batches_completed_sched(void);
@@ -101,18 +63,6 @@ extern void rcu_force_quiescent_state(void);
 extern void rcu_bh_force_quiescent_state(void);
 extern void rcu_sched_force_quiescent_state(void);
 
-#ifdef CONFIG_NO_HZ
-void rcu_enter_nohz(void);
-void rcu_exit_nohz(void);
-#else /* CONFIG_NO_HZ */
-static inline void rcu_enter_nohz(void)
-{
-}
-static inline void rcu_exit_nohz(void)
-{
-}
-#endif /* CONFIG_NO_HZ */
-
 /* A context switch is a grace period for RCU-sched and RCU-bh. */
 static inline int rcu_blocking_is_gp(void)
 {
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 561410f..87f60f0 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -939,15 +939,6 @@ static void rcu_preempt_process_callbacks(void)
 }
 
 /*
- * In classic RCU, call_rcu() is just call_rcu_sched().
- */
-void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
-{
-	call_rcu_sched(head, func);
-}
-EXPORT_SYMBOL_GPL(call_rcu);
-
-/*
  * Wait for an rcu-preempt grace period, but make it happen quickly.
  * But because preemptable RCU does not exist, map to rcu-sched.
  */
-- 
1.7.0.6

[PATCH tip/core/rcu 6/7] rcu: apply TINY_PREEMPT_RCU read-side speedup to TREE_PREEMPT_RCU

[Paul E. McKenney]

Replace one of the ACCESS_ONCE() calls in each of __rcu_read_lock()
and __rcu_read_unlock() with barrier() as suggested by Steve Rostedt in
order to avoid the potential compiler-optimization-induced bug noted by
Mathieu Desnoyers.

Located-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutree_plugin.h |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 87f60f0..e9e0bc7 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -201,7 +201,7 @@ static void rcu_preempt_note_context_switch(int cpu)
  */
 void __rcu_read_lock(void)
 {
-	ACCESS_ONCE(current->rcu_read_lock_nesting)++;
+	current->rcu_read_lock_nesting++;
 	barrier();  /* needed if we ever invoke rcu_read_lock in rcutree.c */
 }
 EXPORT_SYMBOL_GPL(__rcu_read_lock);
@@ -344,7 +344,9 @@ void __rcu_read_unlock(void)
 	struct task_struct *t = current;
 
 	barrier();  /* needed if we ever invoke rcu_read_unlock in rcutree.c */
-	if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
+	--t->rcu_read_lock_nesting;
+	barrier();  /* decrement before load of ->rcu_read_unlock_special */
+	if (t->rcu_read_lock_nesting == 0 &&
 	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
 		rcu_read_unlock_special(t);
 #ifdef CONFIG_PROVE_LOCKING
-- 
1.7.0.6

[PATCH tip/core/rcu 7/7] rcu: add comment stating that list_empty() applies to RCU-protected lists

[Paul E. McKenney]

Because list_empty() does not dereference any RCU-protected pointers, and
further does not pass such pointers to the caller (so that the caller
does not dereference them either), it is safe to use list_empty() on
RCU-protected lists.  There is no need for a list_empty_rcu().  This
commit adds a comment stating this explicitly.

Requested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rculist.h |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index c10b105..f31ef61 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -10,6 +10,15 @@
 #include <linux/rcupdate.h>
 
 /*
+ * Why is there no list_empty_rcu()?  Because list_empty() serves this
+ * purpose.  The list_empty() function fetches the RCU-protected pointer
+ * and compares it to the address of the list head, but neither dereferences
+ * this pointer itself nor provides this pointer to the caller.  Therefore,
+ * it is not necessary to use rcu_dereference(), so that list_empty() can
+ * be used anywhere you would want to use a list_empty_rcu().
+ */
+
+/*
  * return the ->next pointer of a list_head in an rcu safe
  * way, we must not access it directly
  */
-- 
1.7.0.6