Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU updates from Ingo Molnar:
 "The main RCU changes in this cycle are:

   - Idle entry/exit changes, to throttle callback execution and other
     refinements to speed up kbuild, primarily to address performance
     issues located by Tibor Billes.

   - Grace-period related changes, primarily to aid in debugging,
     inspired by an -rt debugging session.

   - Code reorganization moving RCU's source files into its own
     kernel/rcu/ directory.

   - RCU documentation updates

   - Miscellaneous fixes.

  Note, the following commit:

    5c889690aa08 mm: Place preemption point in do_mlockall() loop

  is identical to the commit already in your tree via email:

    22356f447ceb mm: Place preemption point in do_mlockall() loop

  [ Your version of the changelog nicely demonstrates it how kernel oops
    messages should be trimmed properly :-/ ]"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (30 commits)
  rcu: Move RCU-related source code to kernel/rcu directory
  rcu: Fix occurrence of "the the" in checklist.txt
  kthread: Add pointer to vmstat-avoidance patch
  rcu: Update stall-warning documentation
  rcu: Consistent rcu_is_watching() naming
  rcu: Change EXPORT_SYMBOL() to EXPORT_SYMBOL_GPL()
  rcu: Is it safe to enter an RCU read-side critical section?
  rcu: Throttle invoke_rcu_core() invocations due to non-lazy callbacks
  rcu: Throttle rcu_try_advance_all_cbs() execution
  rcu: Remove redundant code from rcu_cleanup_after_idle()
  rcu: Fix CONFIG_RCU_NOCB_CPU_ALL panic on machines with sparse CPU mask
  rcu: Avoid sparse warnings in rcu_nocb_wake trace event
  rcu: Track rcu_nocb_kthread()'s sleeping and awakening
  rcu: Distinguish between NOCB and non-NOCB rcu_callback trace events
  rcu: Add tracing for rcuo no-CBs CPU wakeup handshake
  rcu: Add tracing of normal (non-NOCB) grace-period requests
  rcu: Add tracing to rcu_gp_kthread()
  rcu: Flag lockless access to ->gp_flags with ACCESS_ONCE()
  rcu: Prevent spurious-wakeup DoS attack on rcu_gp_kthread()
  rcu: Improve grace-period start logic
  ...

5 files changed, 118 insertions, 28 deletions

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 4106721c4e5e..45a0a9e81478 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -19,6 +19,21 @@
  */
 
 /*
+ * INIT_LIST_HEAD_RCU - Initialize a list_head visible to RCU readers
+ * @list: list to be initialized
+ *
+ * You should instead use INIT_LIST_HEAD() for normal initialization and
+ * cleanup tasks, when readers have no access to the list being initialized.
+ * However, if the list being initialized is visible to readers, you
+ * need to keep the compiler from being too mischievous.
+ */
+static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
+{
+        ACCESS_ONCE(list->next) = list;
+        ACCESS_ONCE(list->prev) = list;
+}
+
+/*
  * return the ->next pointer of a list_head in an rcu safe
  * way, we must not access it directly
  */
@@ -191,9 +206,13 @@ static inline void list_splice_init_rcu(struct list_head *list,
         if (list_empty(list))
                 return;
 
-        /* "first" and "last" tracking list, so initialize it. */
+        /*
+         * "first" and "last" tracking list, so initialize it.  RCU readers
+         * have access to this list, so we must use INIT_LIST_HEAD_RCU()
+         * instead of INIT_LIST_HEAD().
+         */
 
-        INIT_LIST_HEAD(list);
+        INIT_LIST_HEAD_RCU(list);
 
         /*
          * At this point, the list body still points to the source list.
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index f1f1bc39346b..39cbb889e20d 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -261,6 +261,10 @@ static inline void rcu_user_hooks_switch(struct task_struct *prev,
                 rcu_irq_exit(); \
         } while (0)
 
+#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
+extern bool __rcu_is_watching(void);
+#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
+
 /*
  * Infrastructure to implement the synchronize_() primitives in
  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
@@ -297,10 +301,6 @@ static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
 }
 #endif  /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 
-#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP)
-extern int rcu_is_cpu_idle(void);
-#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP) */
-
 #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
 bool rcu_lockdep_current_cpu_online(void);
 #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
@@ -351,7 +351,7 @@ static inline int rcu_read_lock_held(void)
 {
         if (!debug_lockdep_rcu_enabled())
                 return 1;
-        if (rcu_is_cpu_idle())
+        if (!rcu_is_watching())
                 return 0;
         if (!rcu_lockdep_current_cpu_online())
                 return 0;
@@ -402,7 +402,7 @@ static inline int rcu_read_lock_sched_held(void)
 
         if (!debug_lockdep_rcu_enabled())
                 return 1;
-        if (rcu_is_cpu_idle())
+        if (!rcu_is_watching())
                 return 0;
         if (!rcu_lockdep_current_cpu_online())
                 return 0;
@@ -771,7 +771,7 @@ static inline void rcu_read_lock(void)
         __rcu_read_lock();
         __acquire(RCU);
         rcu_lock_acquire(&rcu_lock_map);
-        rcu_lockdep_assert(!rcu_is_cpu_idle(),
+        rcu_lockdep_assert(rcu_is_watching(),
                            "rcu_read_lock() used illegally while idle");
 }
 
@@ -792,7 +792,7 @@ static inline void rcu_read_lock(void)
  */
 static inline void rcu_read_unlock(void)
 {
-        rcu_lockdep_assert(!rcu_is_cpu_idle(),
+        rcu_lockdep_assert(rcu_is_watching(),
                            "rcu_read_unlock() used illegally while idle");
         rcu_lock_release(&rcu_lock_map);
         __release(RCU);
@@ -821,7 +821,7 @@ static inline void rcu_read_lock_bh(void)
         local_bh_disable();
         __acquire(RCU_BH);
         rcu_lock_acquire(&rcu_bh_lock_map);
-        rcu_lockdep_assert(!rcu_is_cpu_idle(),
+        rcu_lockdep_assert(rcu_is_watching(),
                            "rcu_read_lock_bh() used illegally while idle");
 }
 
@@ -832,7 +832,7 @@ static inline void rcu_read_lock_bh(void)
  */
 static inline void rcu_read_unlock_bh(void)
 {
-        rcu_lockdep_assert(!rcu_is_cpu_idle(),
+        rcu_lockdep_assert(rcu_is_watching(),
                            "rcu_read_unlock_bh() used illegally while idle");
         rcu_lock_release(&rcu_bh_lock_map);
         __release(RCU_BH);
@@ -857,7 +857,7 @@ static inline void rcu_read_lock_sched(void)
         preempt_disable();
         __acquire(RCU_SCHED);
         rcu_lock_acquire(&rcu_sched_lock_map);
-        rcu_lockdep_assert(!rcu_is_cpu_idle(),
+        rcu_lockdep_assert(rcu_is_watching(),
                            "rcu_read_lock_sched() used illegally while idle");
 }
 
@@ -875,7 +875,7 @@ static inline notrace void rcu_read_lock_sched_notrace(void)
  */
 static inline void rcu_read_unlock_sched(void)
 {
-        rcu_lockdep_assert(!rcu_is_cpu_idle(),
+        rcu_lockdep_assert(rcu_is_watching(),
                            "rcu_read_unlock_sched() used illegally while idle");
         rcu_lock_release(&rcu_sched_lock_map);
         __release(RCU_SCHED);
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index e31005ee339e..09ebcbe9fd78 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -132,4 +132,21 @@ static inline void rcu_scheduler_starting(void)
 }
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
+#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
+
+static inline bool rcu_is_watching(void)
+{
+        return __rcu_is_watching();
+}
+
+#else /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
+
+static inline bool rcu_is_watching(void)
+{
+        return true;
+}
+
+
+#endif /* #else defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
+
 #endif /* __LINUX_RCUTINY_H */
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 226169d1bd2b..4b9c81548742 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -90,4 +90,6 @@ extern void exit_rcu(void);
 extern void rcu_scheduler_starting(void);
 extern int rcu_scheduler_active __read_mostly;
 
+extern bool rcu_is_watching(void);
+
 #endif /* __LINUX_RCUTREE_H */
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index ee2376cfaab3..aca382266411 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -39,15 +39,26 @@ TRACE_EVENT(rcu_utilization,
 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
 
 /*
- * Tracepoint for grace-period events: starting and ending a grace
- * period ("start" and "end", respectively), a CPU noting the start
- * of a new grace period or the end of an old grace period ("cpustart"
- * and "cpuend", respectively), a CPU passing through a quiescent
- * state ("cpuqs"), a CPU coming online or going offline ("cpuonl"
- * and "cpuofl", respectively), a CPU being kicked for being too
- * long in dyntick-idle mode ("kick"), a CPU accelerating its new
- * callbacks to RCU_NEXT_READY_TAIL ("AccReadyCB"), and a CPU
- * accelerating its new callbacks to RCU_WAIT_TAIL ("AccWaitCB").
+ * Tracepoint for grace-period events.  Takes a string identifying the
+ * RCU flavor, the grace-period number, and a string identifying the
+ * grace-period-related event as follows:
+ *
+ *      "AccReadyCB": CPU acclerates new callbacks to RCU_NEXT_READY_TAIL.
+ *      "AccWaitCB": CPU accelerates new callbacks to RCU_WAIT_TAIL.
+ *      "newreq": Request a new grace period.
+ *      "start": Start a grace period.
+ *      "cpustart": CPU first notices a grace-period start.
+ *      "cpuqs": CPU passes through a quiescent state.
+ *      "cpuonl": CPU comes online.
+ *      "cpuofl": CPU goes offline.
+ *      "reqwait": GP kthread sleeps waiting for grace-period request.
+ *      "reqwaitsig": GP kthread awakened by signal from reqwait state.
+ *      "fqswait": GP kthread waiting until time to force quiescent states.
+ *      "fqsstart": GP kthread starts forcing quiescent states.
+ *      "fqsend": GP kthread done forcing quiescent states.
+ *      "fqswaitsig": GP kthread awakened by signal from fqswait state.
+ *      "end": End a grace period.
+ *      "cpuend": CPU first notices a grace-period end.
  */
 TRACE_EVENT(rcu_grace_period,
 
@@ -161,6 +172,46 @@ TRACE_EVENT(rcu_grace_period_init,
 );
 
 /*
+ * Tracepoint for RCU no-CBs CPU callback handoffs.  This event is intended
+ * to assist debugging of these handoffs.
+ *
+ * The first argument is the name of the RCU flavor, and the second is
+ * the number of the offloaded CPU are extracted.  The third and final
+ * argument is a string as follows:
+ *
+ *      "WakeEmpty": Wake rcuo kthread, first CB to empty list.
+ *      "WakeOvf": Wake rcuo kthread, CB list is huge.
+ *      "WakeNot": Don't wake rcuo kthread.
+ *      "WakeNotPoll": Don't wake rcuo kthread because it is polling.
+ *      "Poll": Start of new polling cycle for rcu_nocb_poll.
+ *      "Sleep": Sleep waiting for CBs for !rcu_nocb_poll.
+ *      "WokeEmpty": rcuo kthread woke to find empty list.
+ *      "WokeNonEmpty": rcuo kthread woke to find non-empty list.
+ *      "WaitQueue": Enqueue partially done, timed wait for it to complete.
+ *      "WokeQueue": Partial enqueue now complete.
+ */
+TRACE_EVENT(rcu_nocb_wake,
+
+        TP_PROTO(const char *rcuname, int cpu, const char *reason),
+
+        TP_ARGS(rcuname, cpu, reason),
+
+        TP_STRUCT__entry(
+                __field(const char *, rcuname)
+                __field(int, cpu)
+                __field(const char *, reason)
+        ),
+
+        TP_fast_assign(
+                __entry->rcuname = rcuname;
+                __entry->cpu = cpu;
+                __entry->reason = reason;
+        ),
+
+        TP_printk("%s %d %s", __entry->rcuname, __entry->cpu, __entry->reason)
+);
+
+/*
  * Tracepoint for tasks blocking within preemptible-RCU read-side
  * critical sections.  Track the type of RCU (which one day might
  * include SRCU), the grace-period number that the task is blocking
@@ -540,17 +591,17 @@ TRACE_EVENT(rcu_invoke_kfree_callback,
 TRACE_EVENT(rcu_batch_end,
 
         TP_PROTO(const char *rcuname, int callbacks_invoked,
-                 bool cb, bool nr, bool iit, bool risk),
+                 char cb, char nr, char iit, char risk),
 
         TP_ARGS(rcuname, callbacks_invoked, cb, nr, iit, risk),
 
         TP_STRUCT__entry(
                 __field(const char *, rcuname)
                 __field(int, callbacks_invoked)
-                __field(bool, cb)
-                __field(bool, nr)
-                __field(bool, iit)
-                __field(bool, risk)
+                __field(char, cb)
+                __field(char, nr)
+                __field(char, iit)
+                __field(char, risk)
         ),
 
         TP_fast_assign(
@@ -656,6 +707,7 @@ TRACE_EVENT(rcu_barrier,
 #define trace_rcu_future_grace_period(rcuname, gpnum, completed, c, \
                                       level, grplo, grphi, event) \
                                       do { } while (0)
+#define trace_rcu_nocb_wake(rcuname, cpu, reason) do { } while (0)
 #define trace_rcu_preempt_task(rcuname, pid, gpnum) do { } while (0)
 #define trace_rcu_unlock_preempted_task(rcuname, gpnum, pid) do { } while (0)
 #define trace_rcu_quiescent_state_report(rcuname, gpnum, mask, qsmask, level, \