Merge branch 'rcu/next' of git://git.kernel.org/pub/scm/linux/kernel/…

…git/paulmck/linux-rcu into core/rcu

Pull RCU updates from Paul E. McKenney:

  * Remove restrictions on no-CBs CPUs, make RCU_FAST_NO_HZ
    take advantage of numbered callbacks, do additional callback
    accelerations based on numbered callbacks.  Posted to LKML
    at https://lkml.org/lkml/2013/3/18/960.

  * RCU documentation updates.  Posted to LKML at
    https://lkml.org/lkml/2013/3/18/570.

  * Miscellaneous fixes.  Posted to LKML at
    https://lkml.org/lkml/2013/3/18/594.

Signed-off-by: Ingo Molnar <[email protected]>

Documentation/RCU/checklist.txt

@@ -217,9 +217,14 @@ over a rather long period of time, but improvements are always welcome!
 	whether the increased speed is worth it.
 
 8.	Although synchronize_rcu() is slower than is call_rcu(), it
-	usually results in simpler code.  So, unless update performance
-	is critically important or the updaters cannot block,
-	synchronize_rcu() should be used in preference to call_rcu().
+	usually results in simpler code.  So, unless update performance is
+	critically important, the updaters cannot block, or the latency of
+	synchronize_rcu() is visible from userspace, synchronize_rcu()
+	should be used in preference to call_rcu().  Furthermore,
+	kfree_rcu() usually results in even simpler code than does
+	synchronize_rcu() without synchronize_rcu()'s multi-millisecond
+	latency.  So please take advantage of kfree_rcu()'s "fire and
+	forget" memory-freeing capabilities where it applies.
 
 	An especially important property of the synchronize_rcu()
 	primitive is that it automatically self-limits: if grace periods
@@ -268,7 +273,8 @@ over a rather long period of time, but improvements are always welcome!
 	e.	Periodically invoke synchronize_rcu(), permitting a limited
 		number of updates per grace period.
 
-	The same cautions apply to call_rcu_bh() and call_rcu_sched().
+	The same cautions apply to call_rcu_bh(), call_rcu_sched(),
+	call_srcu(), and kfree_rcu().
 
 9.	All RCU list-traversal primitives, which include
 	rcu_dereference(), list_for_each_entry_rcu(), and
@@ -296,9 +302,9 @@ over a rather long period of time, but improvements are always welcome!
 	all currently executing rcu_read_lock()-protected RCU read-side
 	critical sections complete.  It does -not- necessarily guarantee
 	that all currently running interrupts, NMIs, preempt_disable()
-	code, or idle loops will complete.  Therefore, if you do not have
-	rcu_read_lock()-protected read-side critical sections, do -not-
-	use synchronize_rcu().
+	code, or idle loops will complete.  Therefore, if your
+	read-side critical sections are protected by something other
+	than rcu_read_lock(), do -not- use synchronize_rcu().
 
 	Similarly, disabling preemption is not an acceptable substitute
 	for rcu_read_lock().  Code that attempts to use preemption
@@ -401,9 +407,9 @@ over a rather long period of time, but improvements are always welcome!
 	read-side critical sections.  It is the responsibility of the
 	RCU update-side primitives to deal with this.
 
-17.	Use CONFIG_PROVE_RCU, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and
-	the __rcu sparse checks to validate your RCU code.  These
-	can help find problems as follows:
+17.	Use CONFIG_PROVE_RCU, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and the
+	__rcu sparse checks (enabled by CONFIG_SPARSE_RCU_POINTER) to
+	validate your RCU code.  These can help find problems as follows:
 
 	CONFIG_PROVE_RCU: check that accesses to RCU-protected data
 		structures are carried out under the proper RCU

Documentation/RCU/lockdep.txt

@@ -64,6 +64,11 @@ checking of rcu_dereference() primitives:
 		but retain the compiler constraints that prevent duplicating
 		or coalescsing.  This is useful when when testing the
 		value of the pointer itself, for example, against NULL.
+	rcu_access_index(idx):
+		Return the value of the index and omit all barriers, but
+		retain the compiler constraints that prevent duplicating
+		or coalescsing.  This is useful when when testing the
+		value of the index itself, for example, against -1.
 
 The rcu_dereference_check() check expression can be any boolean
 expression, but would normally include a lockdep expression.  However,

Documentation/RCU/rcubarrier.txt

@@ -79,7 +79,20 @@ complete. Pseudo-code using rcu_barrier() is as follows:
    2. Execute rcu_barrier().
    3. Allow the module to be unloaded.
 
-The rcutorture module makes use of rcu_barrier in its exit function
+There are also rcu_barrier_bh(), rcu_barrier_sched(), and srcu_barrier()
+functions for the other flavors of RCU, and you of course must match
+the flavor of rcu_barrier() with that of call_rcu().  If your module
+uses multiple flavors of call_rcu(), then it must also use multiple
+flavors of rcu_barrier() when unloading that module.  For example, if
+it uses call_rcu_bh(), call_srcu() on srcu_struct_1, and call_srcu() on
+srcu_struct_2(), then the following three lines of code will be required
+when unloading:
+
+ 1 rcu_barrier_bh();
+ 2 srcu_barrier(&srcu_struct_1);
+ 3 srcu_barrier(&srcu_struct_2);
+
+The rcutorture module makes use of rcu_barrier() in its exit function
 as follows:
 
  1 static void

Documentation/RCU/stallwarn.txt

@@ -92,14 +92,14 @@ If the CONFIG_RCU_CPU_STALL_INFO kernel configuration parameter is set,
 more information is printed with the stall-warning message, for example:
 
 	INFO: rcu_preempt detected stall on CPU
-	0: (63959 ticks this GP) idle=241/3fffffffffffffff/0
+	0: (63959 ticks this GP) idle=241/3fffffffffffffff/0 softirq=82/543
 	   (t=65000 jiffies)
 
 In kernels with CONFIG_RCU_FAST_NO_HZ, even more information is
 printed:
 
 	INFO: rcu_preempt detected stall on CPU
-	0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 drain=0 . timer not pending
+	0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 softirq=82/543 last_accelerate: a345/d342 nonlazy_posted: 25 .D
 	   (t=65000 jiffies)
 
 The "(64628 ticks this GP)" indicates that this CPU has taken more
@@ -116,13 +116,28 @@ number between the two "/"s is the value of the nesting, which will
 be a small positive number if in the idle loop and a very large positive
 number (as shown above) otherwise.
 
-For CONFIG_RCU_FAST_NO_HZ kernels, the "drain=0" indicates that the CPU is
-not in the process of trying to force itself into dyntick-idle state, the
-"." indicates that the CPU has not given up forcing RCU into dyntick-idle
-mode (it would be "H" otherwise), and the "timer not pending" indicates
-that the CPU has not recently forced RCU into dyntick-idle mode (it
-would otherwise indicate the number of microseconds remaining in this
-forced state).
+The "softirq=" portion of the message tracks the number of RCU softirq
+handlers that the stalled CPU has executed.  The number before the "/"
+is the number that had executed since boot at the time that this CPU
+last noted the beginning of a grace period, which might be the current
+(stalled) grace period, or it might be some earlier grace period (for
+example, if the CPU might have been in dyntick-idle mode for an extended
+time period.  The number after the "/" is the number that have executed
+since boot until the current time.  If this latter number stays constant
+across repeated stall-warning messages, it is possible that RCU's softirq
+handlers are no longer able to execute on this CPU.  This can happen if
+the stalled CPU is spinning with interrupts are disabled, or, in -rt
+kernels, if a high-priority process is starving RCU's softirq handler.
+
+For CONFIG_RCU_FAST_NO_HZ kernels, the "last_accelerate:" prints the
+low-order 16 bits (in hex) of the jiffies counter when this CPU last
+invoked rcu_try_advance_all_cbs() from rcu_needs_cpu() or last invoked
+rcu_accelerate_cbs() from rcu_prepare_for_idle().  The "nonlazy_posted:"
+prints the number of non-lazy callbacks posted since the last call to
+rcu_needs_cpu().  Finally, an "L" indicates that there are currently
+no non-lazy callbacks ("." is printed otherwise, as shown above) and
+"D" indicates that dyntick-idle processing is enabled ("." is printed
+otherwise, for example, if disabled via the "nohz=" kernel boot parameter).
 
 
 Multiple Warnings From One Stall

Documentation/RCU/whatisRCU.txt

@@ -265,9 +265,9 @@ rcu_dereference()
 		rcu_read_lock();
 		p = rcu_dereference(head.next);
 		rcu_read_unlock();
-		x = p->address;
+		x = p->address;	/* BUG!!! */
 		rcu_read_lock();
-		y = p->data;
+		y = p->data;	/* BUG!!! */
 		rcu_read_unlock();
 
 	Holding a reference from one RCU read-side critical section

Documentation/kernel-parameters.txt

@@ -2461,9 +2461,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			In kernels built with CONFIG_RCU_NOCB_CPU=y, set
 			the specified list of CPUs to be no-callback CPUs.
 			Invocation of these CPUs' RCU callbacks will
-			be offloaded to "rcuoN" kthreads created for
-			that purpose.  This reduces OS jitter on the
+			be offloaded to "rcuox/N" kthreads created for
+			that purpose, where "x" is "b" for RCU-bh, "p"
+			for RCU-preempt, and "s" for RCU-sched, and "N"
+			is the CPU number.  This reduces OS jitter on the
 			offloaded CPUs, which can be useful for HPC and
+
 			real-time workloads.  It can also improve energy
 			efficiency for asymmetric multiprocessors.
 
@@ -2487,6 +2490,17 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			leaf rcu_node structure.  Useful for very large
 			systems.
 
+	rcutree.jiffies_till_first_fqs= [KNL,BOOT]
+			Set delay from grace-period initialization to
+			first attempt to force quiescent states.
+			Units are jiffies, minimum value is zero,
+			and maximum value is HZ.
+
+	rcutree.jiffies_till_next_fqs= [KNL,BOOT]
+			Set delay between subsequent attempts to force
+			quiescent states.  Units are jiffies, minimum
+			value is one, and maximum value is HZ.
+
 	rcutree.qhimark=	[KNL,BOOT]
 			Set threshold of queued
 			RCU callbacks over which batch limiting is disabled.
@@ -2501,16 +2515,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 	rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
 			Set timeout for RCU CPU stall warning messages.
 
-	rcutree.jiffies_till_first_fqs= [KNL,BOOT]
-			Set delay from grace-period initialization to
-			first attempt to force quiescent states.
-			Units are jiffies, minimum value is zero,
-			and maximum value is HZ.
+	rcutree.rcu_idle_gp_delay=	[KNL,BOOT]
+			Set wakeup interval for idle CPUs that have
+			RCU callbacks (RCU_FAST_NO_HZ=y).
 
-	rcutree.jiffies_till_next_fqs= [KNL,BOOT]
-			Set delay between subsequent attempts to force
-			quiescent states.  Units are jiffies, minimum
-			value is one, and maximum value is HZ.
+	rcutree.rcu_idle_lazy_gp_delay=	[KNL,BOOT]
+			Set wakeup interval for idle CPUs that have
+			only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
+			Lazy RCU callbacks are those which RCU can
+			prove do nothing more than free memory.
 
 	rcutorture.fqs_duration= [KNL,BOOT]
 			Set duration of force_quiescent_state bursts.

include/linux/list_bl.h

@@ -125,6 +125,11 @@ static inline void hlist_bl_unlock(struct hlist_bl_head *b)
 	__bit_spin_unlock(0, (unsigned long *)b);
 }
 
+static inline bool hlist_bl_is_locked(struct hlist_bl_head *b)
+{
+	return bit_spin_is_locked(0, (unsigned long *)b);
+}
+
 /**
  * hlist_bl_for_each_entry	- iterate over list of given type
  * @tpos:	the type * to use as a loop cursor.

include/linux/rculist_bl.h

@@ -20,7 +20,7 @@ static inline void hlist_bl_set_first_rcu(struct hlist_bl_head *h,
 static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
 {
 	return (struct hlist_bl_node *)
-		((unsigned long)rcu_dereference(h->first) & ~LIST_BL_LOCKMASK);
+		((unsigned long)rcu_dereference_check(h->first, hlist_bl_is_locked(h)) & ~LIST_BL_LOCKMASK);
 }
 
 /**

include/linux/rcupdate.h

@@ -80,6 +80,7 @@ extern void do_trace_rcu_torture_read(char *rcutorturename,
 #define UINT_CMP_LT(a, b)	(UINT_MAX / 2 < (a) - (b))
 #define ULONG_CMP_GE(a, b)	(ULONG_MAX / 2 >= (a) - (b))
 #define ULONG_CMP_LT(a, b)	(ULONG_MAX / 2 < (a) - (b))
+#define ulong2long(a)		(*(long *)(&(a)))
 
 /* Exported common interfaces */
 

include/trace/events/rcu.h

@@ -71,6 +71,58 @@ TRACE_EVENT(rcu_grace_period,
 		  __entry->rcuname, __entry->gpnum, __entry->gpevent)
 );
 
+/*
+ * Tracepoint for future grace-period events, including those for no-callbacks
+ * CPUs.  The caller should pull the data from the rcu_node structure,
+ * other than rcuname, which comes from the rcu_state structure, and event,
+ * which is one of the following:
+ *
+ * "Startleaf": Request a nocb grace period based on leaf-node data.
+ * "Startedleaf": Leaf-node start proved sufficient.
+ * "Startedleafroot": Leaf-node start proved sufficient after checking root.
+ * "Startedroot": Requested a nocb grace period based on root-node data.
+ * "StartWait": Start waiting for the requested grace period.
+ * "ResumeWait": Resume waiting after signal.
+ * "EndWait": Complete wait.
+ * "Cleanup": Clean up rcu_node structure after previous GP.
+ * "CleanupMore": Clean up, and another no-CB GP is needed.
+ */
+TRACE_EVENT(rcu_future_grace_period,
+
+	TP_PROTO(char *rcuname, unsigned long gpnum, unsigned long completed,
+		 unsigned long c, u8 level, int grplo, int grphi,
+		 char *gpevent),
+
+	TP_ARGS(rcuname, gpnum, completed, c, level, grplo, grphi, gpevent),
+
+	TP_STRUCT__entry(
+		__field(char *, rcuname)
+		__field(unsigned long, gpnum)
+		__field(unsigned long, completed)
+		__field(unsigned long, c)
+		__field(u8, level)
+		__field(int, grplo)
+		__field(int, grphi)
+		__field(char *, gpevent)
+	),
+
+	TP_fast_assign(
+		__entry->rcuname = rcuname;
+		__entry->gpnum = gpnum;
+		__entry->completed = completed;
+		__entry->c = c;
+		__entry->level = level;
+		__entry->grplo = grplo;
+		__entry->grphi = grphi;
+		__entry->gpevent = gpevent;
+	),
+
+	TP_printk("%s %lu %lu %lu %u %d %d %s",
+		  __entry->rcuname, __entry->gpnum, __entry->completed,
+		  __entry->c, __entry->level, __entry->grplo, __entry->grphi,
+		  __entry->gpevent)
+);
+
 /*
  * Tracepoint for grace-period-initialization events.  These are
  * distinguished by the type of RCU, the new grace-period number, the
@@ -601,6 +653,9 @@ TRACE_EVENT(rcu_barrier,
 #define trace_rcu_grace_period(rcuname, gpnum, gpevent) do { } while (0)
 #define trace_rcu_grace_period_init(rcuname, gpnum, level, grplo, grphi, \
 				    qsmask) do { } while (0)
+#define trace_rcu_future_grace_period(rcuname, gpnum, completed, c, \
+				      level, grplo, grphi, event) \
+				      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, \