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

Pull RCU update from Ingo Molnar:
 "The major features of this tree are:

     1. A first version of no-callbacks CPUs.  This version prohibits
        offlining CPU 0, but only when enabled via CONFIG_RCU_NOCB_CPU=y.
        Relaxing this constraint is in progress, but not yet ready
        for prime time.  These commits were posted to LKML at
        https://lkml.org/lkml/2012/10/30/724.

     2. Changes to SRCU that allows statically initialized srcu_struct
        structures.  These commits were posted to LKML at
        https://lkml.org/lkml/2012/10/30/296.

     3. Restructuring of RCU's debugfs output.  These commits were posted
        to LKML at https://lkml.org/lkml/2012/10/30/341.

     4. Additional CPU-hotplug/RCU improvements, posted to LKML at
        https://lkml.org/lkml/2012/10/30/327.
        Note that the commit eliminating __stop_machine() was judged to
        be too-high of risk, so is deferred to 3.9.

     5. Changes to RCU's idle interface, most notably a new module
        parameter that redirects normal grace-period operations to
        their expedited equivalents.  These were posted to LKML at
        https://lkml.org/lkml/2012/10/30/739.

     6. Additional diagnostics for RCU's CPU stall warning facility,
        posted to LKML at https://lkml.org/lkml/2012/10/30/315.
        The most notable change reduces the
        default RCU CPU stall-warning time from 60 seconds to 21 seconds,
        so that it once again happens sooner than the softlockup timeout.

     7. Documentation updates, which were posted to LKML at
        https://lkml.org/lkml/2012/10/30/280.
        A couple of late-breaking changes were posted at
        https://lkml.org/lkml/2012/11/16/634 and
        https://lkml.org/lkml/2012/11/16/547.

     8. Miscellaneous fixes, which were posted to LKML at
        https://lkml.org/lkml/2012/10/30/309.

     9. Finally, a fix for an lockdep-RCU splat was posted to LKML
        at https://lkml.org/lkml/2012/11/7/486."

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (49 commits)
  context_tracking: New context tracking susbsystem
  sched: Mark RCU reader in sched_show_task()
  rcu: Separate accounting of callbacks from callback-free CPUs
  rcu: Add callback-free CPUs
  rcu: Add documentation for the new rcuexp debugfs trace file
  rcu: Update documentation for TREE_RCU debugfs tracing
  rcu: Reduce default RCU CPU stall warning timeout
  rcu: Fix TINY_RCU rcu_is_cpu_rrupt_from_idle check
  rcu: Clarify memory-ordering properties of grace-period primitives
  rcu: Add new rcutorture module parameters to start/end test messages
  rcu: Remove list_for_each_continue_rcu()
  rcu: Fix batch-limit size problem
  rcu: Add tracing for synchronize_sched_expedited()
  rcu: Remove old debugfs interfaces and also RCU flavor name
  rcu: split 'rcuhier' to each flavor
  rcu: split 'rcugp' to each flavor
  rcu: split 'rcuboost' to each flavor
  rcu: split 'rcubarrier' to each flavor
  rcu: Fix tracing formatting
  rcu: Remove the interface "rcudata.csv"
  ...

39 files changed, 1493 insertions, 628 deletions

diff --git a/Documentation/RCU/RTFP.txt b/Documentation/RCU/RTFP.txt
index 7c1dfb19fc4..7f40c72a9c5 100644
--- a/Documentation/RCU/RTFP.txt
+++ b/Documentation/RCU/RTFP.txt
@@ -186,7 +186,7 @@ Bibtex Entries
 
 @article{Kung80
 ,author="H. T. Kung and Q. Lehman"
-,title="Concurrent Maintenance of Binary Search Trees"
+,title="Concurrent Manipulation of Binary Search Trees"
 ,Year="1980"
 ,Month="September"
 ,journal="ACM Transactions on Database Systems"
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index cdb20d41a44..31ef8fe07f8 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -271,15 +271,14 @@ over a rather long period of time, but improvements are always welcome!
 	The same cautions apply to call_rcu_bh() and call_rcu_sched().
 
 9.	All RCU list-traversal primitives, which include
-	rcu_dereference(), list_for_each_entry_rcu(),
-	list_for_each_continue_rcu(), and list_for_each_safe_rcu(),
-	must be either within an RCU read-side critical section or
-	must be protected by appropriate update-side locks.  RCU
-	read-side critical sections are delimited by rcu_read_lock()
-	and rcu_read_unlock(), or by similar primitives such as
-	rcu_read_lock_bh() and rcu_read_unlock_bh(), in which case
-	the matching rcu_dereference() primitive must be used in order
-	to keep lockdep happy, in this case, rcu_dereference_bh().
+	rcu_dereference(), list_for_each_entry_rcu(), and
+	list_for_each_safe_rcu(), must be either within an RCU read-side
+	critical section or must be protected by appropriate update-side
+	locks.	RCU read-side critical sections are delimited by
+	rcu_read_lock() and rcu_read_unlock(), or by similar primitives
+	such as rcu_read_lock_bh() and rcu_read_unlock_bh(), in which
+	case the matching rcu_dereference() primitive must be used in
+	order to keep lockdep happy, in this case, rcu_dereference_bh().
 
 	The reason that it is permissible to use RCU list-traversal
 	primitives when the update-side lock is held is that doing so
diff --git a/Documentation/RCU/listRCU.txt b/Documentation/RCU/listRCU.txt
index 4349c1487e9..adb5a378284 100644
--- a/Documentation/RCU/listRCU.txt
+++ b/Documentation/RCU/listRCU.txt
@@ -205,7 +205,7 @@ RCU ("read-copy update") its name.  The RCU code is as follows:
 				audit_copy_rule(&ne->rule, &e->rule);
 				ne->rule.action = newaction;
 				ne->rule.file_count = newfield_count;
-				list_replace_rcu(e, ne);
+				list_replace_rcu(&e->list, &ne->list);
 				call_rcu(&e->rcu, audit_free_rule);
 				return 0;
 			}
diff --git a/Documentation/RCU/rcuref.txt b/Documentation/RCU/rcuref.txt
index 4202ad09313..141d531aa14 100644
--- a/Documentation/RCU/rcuref.txt
+++ b/Documentation/RCU/rcuref.txt
@@ -20,7 +20,7 @@ release_referenced()			delete()
 {					{
     ...					    write_lock(&list_lock);
     atomic_dec(&el->rc, relfunc)	    ...
-    ...					    delete_element
+    ...					    remove_element
 }					    write_unlock(&list_lock);
  					    ...
 					    if (atomic_dec_and_test(&el->rc))
@@ -52,7 +52,7 @@ release_referenced()			delete()
 {					{
     ...					    spin_lock(&list_lock);
     if (atomic_dec_and_test(&el->rc))       ...
-        call_rcu(&el->head, el_free);       delete_element
+        call_rcu(&el->head, el_free);       remove_element
     ...                                     spin_unlock(&list_lock);
 } 					    ...
 					    if (atomic_dec_and_test(&el->rc))
@@ -64,3 +64,60 @@ Sometimes, a reference to the element needs to be obtained in the
 update (write) stream.  In such cases, atomic_inc_not_zero() might be
 overkill, since we hold the update-side spinlock.  One might instead
 use atomic_inc() in such cases.
+
+It is not always convenient to deal with "FAIL" in the
+search_and_reference() code path.  In such cases, the
+atomic_dec_and_test() may be moved from delete() to el_free()
+as follows:
+
+1.					2.
+add()					search_and_reference()
+{					{
+    alloc_object			    rcu_read_lock();
+    ...					    search_for_element
+    atomic_set(&el->rc, 1);		    atomic_inc(&el->rc);
+    spin_lock(&list_lock);		    ...
+
+    add_element				    rcu_read_unlock();
+    ...					}
+    spin_unlock(&list_lock);		4.
+}					delete()
+3.					{
+release_referenced()			    spin_lock(&list_lock);
+{					    ...
+    ...					    remove_element
+    if (atomic_dec_and_test(&el->rc))       spin_unlock(&list_lock);
+        kfree(el);			    ...
+    ...                                     call_rcu(&el->head, el_free);
+} 					    ...
+5.					}
+void el_free(struct rcu_head *rhp)
+{
+    release_referenced();
+}
+
+The key point is that the initial reference added by add() is not removed
+until after a grace period has elapsed following removal.  This means that
+search_and_reference() cannot find this element, which means that the value
+of el->rc cannot increase.  Thus, once it reaches zero, there are no
+readers that can or ever will be able to reference the element.  The
+element can therefore safely be freed.  This in turn guarantees that if
+any reader finds the element, that reader may safely acquire a reference
+without checking the value of the reference counter.
+
+In cases where delete() can sleep, synchronize_rcu() can be called from
+delete(), so that el_free() can be subsumed into delete as follows:
+
+4.
+delete()
+{
+    spin_lock(&list_lock);
+    ...
+    remove_element
+    spin_unlock(&list_lock);
+    ...
+    synchronize_rcu();
+    if (atomic_dec_and_test(&el->rc))
+    	kfree(el);
+    ...
+}
diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt
index 672d1908325..c776968f446 100644
--- a/Documentation/RCU/trace.txt
+++ b/Documentation/RCU/trace.txt
@@ -10,51 +10,63 @@ for rcutree and next for rcutiny.
 
 CONFIG_TREE_RCU and CONFIG_TREE_PREEMPT_RCU debugfs Files and Formats
 
-These implementations of RCU provides several debugfs files under the
+These implementations of RCU provide several debugfs directories under the
 top-level directory "rcu":
 
-rcu/rcudata:
+rcu/rcu_bh
+rcu/rcu_preempt
+rcu/rcu_sched
+
+Each directory contains files for the corresponding flavor of RCU.
+Note that rcu/rcu_preempt is only present for CONFIG_TREE_PREEMPT_RCU.
+For CONFIG_TREE_RCU, the RCU flavor maps onto the RCU-sched flavor,
+so that activity for both appears in rcu/rcu_sched.
+
+In addition, the following file appears in the top-level directory:
+rcu/rcutorture.  This file displays rcutorture test progress.  The output
+of "cat rcu/rcutorture" looks as follows:
+
+rcutorture test sequence: 0 (test in progress)
+rcutorture update version number: 615
+
+The first line shows the number of rcutorture tests that have completed
+since boot.  If a test is currently running, the "(test in progress)"
+string will appear as shown above.  The second line shows the number of
+update cycles that the current test has started, or zero if there is
+no test in progress.
+
+
+Within each flavor directory (rcu/rcu_bh, rcu/rcu_sched, and possibly
+also rcu/rcu_preempt) the following files will be present:
+
+rcudata:
 	Displays fields in struct rcu_data.
-rcu/rcudata.csv:
-	Comma-separated values spreadsheet version of rcudata.
-rcu/rcugp:
+rcuexp:
+	Displays statistics for expedited grace periods.
+rcugp:
 	Displays grace-period counters.
-rcu/rcuhier:
+rcuhier:
 	Displays the struct rcu_node hierarchy.
-rcu/rcu_pending:
+rcu_pending:
 	Displays counts of the reasons rcu_pending() decided that RCU had
 	work to do.
-rcu/rcutorture:
-	Displays rcutorture test progress.
-rcu/rcuboost:
+rcuboost:
 	Displays RCU boosting statistics.  Only present if
 	CONFIG_RCU_BOOST=y.
 
-The output of "cat rcu/rcudata" looks as follows:
-
-rcu_sched:
-  0 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=545/1/0 df=50 of=0 ql=163 qs=NRW. kt=0/W/0 ktl=ebc3 b=10 ci=153737 co=0 ca=0
-  1 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=967/1/0 df=58 of=0 ql=634 qs=NRW. kt=0/W/1 ktl=58c b=10 ci=191037 co=0 ca=0
-  2 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=1081/1/0 df=175 of=0 ql=74 qs=N.W. kt=0/W/2 ktl=da94 b=10 ci=75991 co=0 ca=0
-  3 c=20942 g=20943 pq=1 pgp=20942 qp=1 dt=1846/0/0 df=404 of=0 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=72261 co=0 ca=0
-  4 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=369/1/0 df=83 of=0 ql=48 qs=N.W. kt=0/W/4 ktl=e0e7 b=10 ci=128365 co=0 ca=0
-  5 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=381/1/0 df=64 of=0 ql=169 qs=NRW. kt=0/W/5 ktl=fb2f b=10 ci=164360 co=0 ca=0
-  6 c=20972 g=20973 pq=1 pgp=20973 qp=0 dt=1037/1/0 df=183 of=0 ql=62 qs=N.W. kt=0/W/6 ktl=d2ad b=10 ci=65663 co=0 ca=0
-  7 c=20897 g=20897 pq=1 pgp=20896 qp=0 dt=1572/0/0 df=382 of=0 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=75006 co=0 ca=0
-rcu_bh:
-  0 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=545/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/0 ktl=ebc3 b=10 ci=0 co=0 ca=0
-  1 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=967/1/0 df=3 of=0 ql=0 qs=.... kt=0/W/1 ktl=58c b=10 ci=151 co=0 ca=0
-  2 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1081/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/2 ktl=da94 b=10 ci=0 co=0 ca=0
-  3 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1846/0/0 df=8 of=0 ql=0 qs=.... kt=0/W/3 ktl=d1cd b=10 ci=0 co=0 ca=0
-  4 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=369/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/4 ktl=e0e7 b=10 ci=0 co=0 ca=0
-  5 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=381/1/0 df=4 of=0 ql=0 qs=.... kt=0/W/5 ktl=fb2f b=10 ci=0 co=0 ca=0
-  6 c=1480 g=1480 pq=1 pgp=1480 qp=0 dt=1037/1/0 df=6 of=0 ql=0 qs=.... kt=0/W/6 ktl=d2ad b=10 ci=0 co=0 ca=0
-  7 c=1474 g=1474 pq=1 pgp=1473 qp=0 dt=1572/0/0 df=8 of=0 ql=0 qs=.... kt=0/W/7 ktl=cf15 b=10 ci=0 co=0 ca=0
-
-The first section lists the rcu_data structures for rcu_sched, the second
-for rcu_bh.  Note that CONFIG_TREE_PREEMPT_RCU kernels will have an
-additional section for rcu_preempt.  Each section has one line per CPU,
-or eight for this 8-CPU system.  The fields are as follows:
+The output of "cat rcu/rcu_preempt/rcudata" looks as follows:
+
+  0!c=30455 g=30456 pq=1 qp=1 dt=126535/140000000000000/0 df=2002 of=4 ql=0/0 qs=N... b=10 ci=74572 nci=0 co=1131 ca=716
+  1!c=30719 g=30720 pq=1 qp=0 dt=132007/140000000000000/0 df=1874 of=10 ql=0/0 qs=N... b=10 ci=123209 nci=0 co=685 ca=982
+  2!c=30150 g=30151 pq=1 qp=1 dt=138537/140000000000000/0 df=1707 of=8 ql=0/0 qs=N... b=10 ci=80132 nci=0 co=1328 ca=1458
+  3 c=31249 g=31250 pq=1 qp=0 dt=107255/140000000000000/0 df=1749 of=6 ql=0/450 qs=NRW. b=10 ci=151700 nci=0 co=509 ca=622
+  4!c=29502 g=29503 pq=1 qp=1 dt=83647/140000000000000/0 df=965 of=5 ql=0/0 qs=N... b=10 ci=65643 nci=0 co=1373 ca=1521
+  5 c=31201 g=31202 pq=1 qp=1 dt=70422/0/0 df=535 of=7 ql=0/0 qs=.... b=10 ci=58500 nci=0 co=764 ca=698
+  6!c=30253 g=30254 pq=1 qp=1 dt=95363/140000000000000/0 df=780 of=5 ql=0/0 qs=N... b=10 ci=100607 nci=0 co=1414 ca=1353
+  7 c=31178 g=31178 pq=1 qp=0 dt=91536/0/0 df=547 of=4 ql=0/0 qs=.... b=10 ci=109819 nci=0 co=1115 ca=969
+
+This file has one line per CPU, or eight for this 8-CPU system.
+The fields are as follows:
 
 o	The number at the beginning of each line is the CPU number.
 	CPUs numbers followed by an exclamation mark are offline,
@@ -64,11 +76,13 @@ o	The number at the beginning of each line is the CPU number.
 	substantially larger than the number of actual CPUs.
 
 o	"c" is the count of grace periods that this CPU believes have
-	completed.  Offlined CPUs and CPUs in dynticks idle mode may
-	lag quite a ways behind, for example, CPU 6 under "rcu_sched"
-	above, which has been offline through not quite 40,000 RCU grace
-	periods.  It is not unusual to see CPUs lagging by thousands of
-	grace periods.
+	completed.  Offlined CPUs and CPUs in dynticks idle mode may lag
+	quite a ways behind, for example, CPU 4 under "rcu_sched" above,
+	which has been offline through 16 RCU grace periods.  It is not
+	unusual to see offline CPUs lagging by thousands of grace periods.
+	Note that although the grace-period number is an unsigned long,
+	it is printed out as a signed long to allow more human-friendly
+	representation near boot time.
 
 o	"g" is the count of grace periods that this CPU believes have
 	started.  Again, offlined CPUs and CPUs in dynticks idle mode
@@ -84,30 +98,25 @@ o	"pq" indicates that this CPU has passed through a quiescent state
 	CPU has not yet reported that fact, (2) some other CPU has not
 	yet reported for this grace period, or (3) both.
 
-o	"pgp" indicates which grace period the last-observed quiescent
-	state for this CPU corresponds to.  This is important for handling
-	the race between CPU 0 reporting an extended dynticks-idle
-	quiescent state for CPU 1 and CPU 1 suddenly waking up and
-	reporting its own quiescent state.  If CPU 1 was the last CPU
-	for the current grace period, then the CPU that loses this race
-	will attempt to incorrectly mark CPU 1 as having checked in for
-	the next grace period!
-
 o	"qp" indicates that RCU still expects a quiescent state from
 	this CPU.  Offlined CPUs and CPUs in dyntick idle mode might
 	well have qp=1, which is OK: RCU is still ignoring them.
 
 o	"dt" is the current value of the dyntick counter that is incremented
-	when entering or leaving dynticks idle state, either by the
-	scheduler or by irq.  This number is even if the CPU is in
-	dyntick idle mode and odd otherwise.  The number after the first
-	"/" is the interrupt nesting depth when in dyntick-idle state,
-	or one greater than the interrupt-nesting depth otherwise.
-	The number after the second "/" is the NMI nesting depth.
+	when entering or leaving idle, either due to a context switch or
+	due to an interrupt.  This number is even if the CPU is in idle
+	from RCU's viewpoint and odd otherwise.  The number after the
+	first "/" is the interrupt nesting depth when in idle state,
+	or a large number added to the interrupt-nesting depth when
+	running a non-idle task.  Some architectures do not accurately
+	count interrupt nesting when running in non-idle kernel context,
+	which can result in interesting anomalies such as negative
+	interrupt-nesting levels.  The number after the second "/"
+	is the NMI nesting depth.
 
 o	"df" is the number of times that some other CPU has forced a
 	quiescent state on behalf of this CPU due to this CPU being in
-	dynticks-idle state.
+	idle state.
 
 o	"of" is the number of times that some other CPU has forced a
 	quiescent state on behalf of this CPU due to this CPU being
@@ -120,9 +129,13 @@ o	"of" is the number of times that some other CPU has forced a
 	error, so it makes sense to err conservatively.
 
 o	"ql" is the number of RCU callbacks currently residing on
-	this CPU.  This is the total number of callbacks, regardless
-	of what state they are in (new, waiting for grace period to
-	start, waiting for grace period to end, ready to invoke).
+	this CPU.  The first number is the number of "lazy" callbacks
+	that are known to RCU to only be freeing memory, and the number
+	after the "/" is the total number of callbacks, lazy or not.
+	These counters count callbacks regardless of what phase of
+	grace-period processing that they are in (new, waiting for
+	grace period to start, waiting for grace period to end, ready
+	to invoke).
 
 o	"qs" gives an indication of the state of the callback queue
 	with four characters:
@@ -150,6 +163,43 @@ o	"qs" gives an indication of the state of the callback queue
 	If there are no callbacks in a given one of the above states,
 	the corresponding character is replaced by ".".
 
+o	"b" is the batch limit for this CPU.  If more than this number
+	of RCU callbacks is ready to invoke, then the remainder will
+	be deferred.
+
+o	"ci" is the number of RCU callbacks that have been invoked for
+	this CPU.  Note that ci+nci+ql is the number of callbacks that have
+	been registered in absence of CPU-hotplug activity.
+
+o	"nci" is the number of RCU callbacks that have been offloaded from
+	this CPU.  This will always be zero unless the kernel was built
+	with CONFIG_RCU_NOCB_CPU=y and the "rcu_nocbs=" kernel boot
+	parameter was specified.
+
+o	"co" is the number of RCU callbacks that have been orphaned due to
+	this CPU going offline.  These orphaned callbacks have been moved
+	to an arbitrarily chosen online CPU.
+
+o	"ca" is the number of RCU callbacks that have been adopted by this
+	CPU due to other CPUs going offline.  Note that ci+co-ca+ql is
+	the number of RCU callbacks registered on this CPU.
+
+
+Kernels compiled with CONFIG_RCU_BOOST=y display the following from
+/debug/rcu/rcu_preempt/rcudata:
+
+  0!c=12865 g=12866 pq=1 qp=1 dt=83113/140000000000000/0 df=288 of=11 ql=0/0 qs=N... kt=0/O ktl=944 b=10 ci=60709 nci=0 co=748 ca=871
+  1 c=14407 g=14408 pq=1 qp=0 dt=100679/140000000000000/0 df=378 of=7 ql=0/119 qs=NRW. kt=0/W ktl=9b6 b=10 ci=109740 nci=0 co=589 ca=485
+  2 c=14407 g=14408 pq=1 qp=0 dt=105486/0/0 df=90 of=9 ql=0/89 qs=NRW. kt=0/W ktl=c0c b=10 ci=83113 nci=0 co=533 ca=490
+  3 c=14407 g=14408 pq=1 qp=0 dt=107138/0/0 df=142 of=8 ql=0/188 qs=NRW. kt=0/W ktl=b96 b=10 ci=121114 nci=0 co=426 ca=290
+  4 c=14405 g=14406 pq=1 qp=1 dt=50238/0/0 df=706 of=7 ql=0/0 qs=.... kt=0/W ktl=812 b=10 ci=34929 nci=0 co=643 ca=114
+  5!c=14168 g=14169 pq=1 qp=0 dt=45465/140000000000000/0 df=161 of=11 ql=0/0 qs=N... kt=0/O ktl=b4d b=10 ci=47712 nci=0 co=677 ca=722
+  6 c=14404 g=14405 pq=1 qp=0 dt=59454/0/0 df=94 of=6 ql=0/0 qs=.... kt=0/W ktl=e57 b=10 ci=55597 nci=0 co=701 ca=811
+  7 c=14407 g=14408 pq=1 qp=1 dt=68850/0/0 df=31 of=8 ql=0/0 qs=.... kt=0/W ktl=14bd b=10 ci=77475 nci=0 co=508 ca=1042
+
+This is similar to the output discussed above, but contains the following
+additional fields:
+
 o	"kt" is the per-CPU kernel-thread state.  The digit preceding
 	the first slash is zero if there is no work pending and 1
 	otherwise.  The character between the first pair of slashes is
@@ -184,35 +234,51 @@ o	"ktl" is the low-order 16 bits (in hexadecimal) of the count of
 
 	This field is displayed only for CONFIG_RCU_BOOST kernels.
 
-o	"b" is the batch limit for this CPU.  If more than this number
-	of RCU callbacks is ready to invoke, then the remainder will
-	be deferred.
 
-o	"ci" is the number of RCU callbacks that have been invoked for
-	this CPU.  Note that ci+ql is the number of callbacks that have
-	been registered in absence of CPU-hotplug activity.
+The output of "cat rcu/rcu_preempt/rcuexp" looks as follows:
 
-o	"co" is the number of RCU callbacks that have been orphaned due to
-	this CPU going offline.  These orphaned callbacks have been moved
-	to an arbitrarily chosen online CPU.
+s=21872 d=21872 w=0 tf=0 wd1=0 wd2=0 n=0 sc=21872 dt=21872 dl=0 dx=21872
+
+These fields are as follows:
+
+o	"s" is the starting sequence number.
 
-o	"ca" is the number of RCU callbacks that have been adopted due to
-	other CPUs going offline.  Note that ci+co-ca+ql is the number of
-	RCU callbacks registered on this CPU.
+o	"d" is the ending sequence number.  When the starting and ending
+	numbers differ, there is an expedited grace period in progress.
 
-There is also an rcu/rcudata.csv file with the same information in
-comma-separated-variable spreadsheet format.
+o	"w" is the number of times that the sequence numbers have been
+	in danger of wrapping.
 
+o	"tf" is the number of times that contention has resulted in a
+	failure to begin an expedited grace period.
 
-The output of "cat rcu/rcugp" looks as follows:
+o	"wd1" and "wd2" are the number of times that an attempt to
+	start an expedited grace period found that someone else had
+	completed an expedited grace period that satisfies the
+	attempted request.  "Our work is done."
 
-rcu_sched: completed=33062  gpnum=33063
-rcu_bh: completed=464  gpnum=464
+o	"n" is number of times that contention was so great that
+	the request was demoted from an expedited grace period to
+	a normal grace period.
+
+o	"sc" is the number of times that the attempt to start a
+	new expedited grace period succeeded.
+
+o	"dt" is the number of times that we attempted to update
+	the "d" counter.
+
+o	"dl" is the number of times that we failed to update the "d"
+	counter.
+
+o	"dx" is the number of times that we succeeded in updating
+	the "d" counter.
 
-Again, this output is for both "rcu_sched" and "rcu_bh".  Note that
-kernels built with CONFIG_TREE_PREEMPT_RCU will have an additional
-"rcu_preempt" line.  The fields are taken from the rcu_state structure,
-and are as follows:
+
+The output of "cat rcu/rcu_preempt/rcugp" looks as follows:
+
+completed=31249  gpnum=31250  age=1  max=18
+
+These fields are taken from the rcu_state structure, and are as follows:
 
 o	"completed" is the number of grace periods that have completed.
 	It is comparable to the "c" field from rcu/rcudata in that a
@@ -220,44 +286,42 @@ o	"completed" is the number of grace periods that have completed.
 	that the corresponding RCU grace period has completed.
 
 o	"gpnum" is the number of grace periods that have started.  It is
-	comparable to the "g" field from rcu/rcudata in that a CPU
-	whose "g" field matches the value of "gpnum" is aware that the
-	corresponding RCU grace period has started.
+	similarly comparable to the "g" field from rcu/rcudata in that
+	a CPU whose "g" field matches the value of "gpnum" is aware that
+	the corresponding RCU grace period has started.
+
+	If these two fields are equal, then there is no grace period
+	in progress, in other words, RCU is idle.  On the other hand,
+	if the two fields differ (as they are above), then an RCU grace
+	period is in progress.
 
-	If these two fields are equal (as they are for "rcu_bh" above),
-	then there is no grace period in progress, in other words, RCU
-	is idle.  On the other hand, if the two fields differ (as they
-	do for "rcu_sched" above), then an RCU grace period is in progress.
+o	"age" is the number of jiffies that the current grace period
+	has extended for, or zero if there is no grace period currently
+	in effect.
 
+o	"max" is the age in jiffies of the longest-duration grace period
+	thus far.
 
-The output of "cat rcu/rcuhier" looks as follows, with very long lines:
+The output of "cat rcu/rcu_preempt/rcuhier" looks as follows:
 
-c=6902 g=6903 s=2 jfq=3 j=72c7 nfqs=13142/nfqsng=0(13142) fqlh=6
-1/1 ..>. 0:127 ^0
-3/3 ..>. 0:35 ^0    0/0 ..>. 36:71 ^1    0/0 ..>. 72:107 ^2    0/0 ..>. 108:127 ^3
-3/3f ..>. 0:5 ^0    2/3 ..>. 6:11 ^1    0/0 ..>. 12:17 ^2    0/0 ..>. 18:23 ^3    0/0 ..>. 24:29 ^4    0/0 ..>. 30:35 ^5    0/0 ..>. 36:41 ^0    0/0 ..>. 42:47 ^1    0/0 ..>. 48:53 ^2    0/0 ..>. 54:59 ^3    0/0 ..>. 60:65 ^4    0/0 ..>. 66:71 ^5    0/0 ..>. 72:77 ^0    0/0 ..>. 78:83 ^1    0/0 ..>. 84:89 ^2    0/0 ..>. 90:95 ^3    0/0 ..>. 96:101 ^4    0/0 ..>. 102:107 ^5    0/0 ..>. 108:113 ^0    0/0 ..>. 114:119 ^1    0/0 ..>. 120:125 ^2    0/0 ..>. 126:127 ^3
-rcu_bh:
-c=-226 g=-226 s=1 jfq=-5701 j=72c7 nfqs=88/nfqsng=0(88) fqlh=0
-0/1 ..>. 0:127 ^0
-0/3 ..>. 0:35 ^0    0/0 ..>. 36:71 ^1    0/0 ..>. 72:107 ^2    0/0 ..>. 108:127 ^3
-0/3f ..>. 0:5 ^0    0/3 ..>. 6:11 ^1    0/0 ..>. 12:17 ^2    0/0 ..>. 18:23 ^3    0/0 ..>. 24:29 ^4    0/0 ..>. 30:35 ^5    0/0 ..>. 36:41 ^0    0/0 ..>. 42:47 ^1    0/0 ..>. 48:53 ^2    0/0 ..>. 54:59 ^3    0/0 ..>. 60:65 ^4    0/0 ..>. 66:71 ^5    0/0 ..>. 72:77 ^0    0/0 ..>. 78:83 ^1    0/0 ..>. 84:89 ^2    0/0 ..>. 90:95 ^3    0/0 ..>. 96:101 ^4    0/0 ..>. 102:107 ^5    0/0 ..>. 108:113 ^0    0/0 ..>. 114:119 ^1    0/0 ..>. 120:125 ^2    0/0 ..>. 126:127 ^3
+c=14407 g=14408 s=0 jfq=2 j=c863 nfqs=12040/nfqsng=0(12040) fqlh=1051 oqlen=0/0
+3/3 ..>. 0:7 ^0
+e/e ..>. 0:3 ^0    d/d ..>. 4:7 ^1
 
-This is once again split into "rcu_sched" and "rcu_bh" portions,
-and CONFIG_TREE_PREEMPT_RCU kernels will again have an additional
-"rcu_preempt" section.  The fields are as follows:
+The fields are as follows:
 
-o	"c" is exactly the same as "completed" under rcu/rcugp.
+o	"c" is exactly the same as "completed" under rcu/rcu_preempt/rcugp.
 
-o	"g" is exactly the same as "gpnum" under rcu/rcugp.
+o	"g" is exactly the same as "gpnum" under rcu/rcu_preempt/rcugp.
 
-o	"s" is the "signaled" state that drives force_quiescent_state()'s
+o	"s" is the current state of the force_quiescent_state()
 	state machine.
 
 o	"jfq" is the number of jiffies remaining for this grace period
 	before force_quiescent_state() is invoked to help push things
-	along.  Note that CPUs in dyntick-idle mode throughout the grace
-	period will not report on their own, but rather must be check by
-	some other CPU via force_quiescent_state().
+	along.	Note that CPUs in idle mode throughout the grace period
+	will not report on their own, but rather must be check by some
+	other CPU via force_quiescent_state().
 
 o	"j" is the low-order four hex digits of the jiffies counter.
 	Yes, Paul did run into a number of problems that turned out to
@@ -268,7 +332,8 @@ o	"nfqs" is the number of calls to force_quiescent_state() since
 
 o	"nfqsng" is the number of useless calls to force_quiescent_state(),
 	where there wasn't actually a grace period active.  This can
-	happen due to races.  The number in parentheses is the difference
+	no longer happen due to grace-period processing being pushed
+	into a kthread.  The number in parentheses is the difference
 	between "nfqs" and "nfqsng", or the number of times that
 	force_quiescent_state() actually did some real work.
 
@@ -276,28 +341,27 @@ o	"fqlh" is the number of calls to force_quiescent_state() that
 	exited immediately (without even being counted in nfqs above)
 	due to contention on ->fqslock.
 
-o	Each element of the form "1/1 0:127 ^0" represents one struct
-	rcu_node.  Each line represents one level of the hierarchy, from
-	root to leaves.  It is best to think of the rcu_data structures
-	as forming yet another level after the leaves.  Note that there
-	might be either one, two, or three levels of rcu_node structures,
-	depending on the relationship between CONFIG_RCU_FANOUT and
-	CONFIG_NR_CPUS.
+o	Each element of the form "3/3 ..>. 0:7 ^0" represents one rcu_node
+	structure.  Each line represents one level of the hierarchy,
+	from root to leaves.  It is best to think of the rcu_data
+	structures as forming yet another level after the leaves.
+	Note that there might be either one, two, three, or even four
+	levels of rcu_node structures, depending on the relationship
+	between CONFIG_RCU_FANOUT, CONFIG_RCU_FANOUT_LEAF (possibly
+	adjusted using the rcu_fanout_leaf kernel boot parameter), and
+	CONFIG_NR_CPUS (possibly adjusted using the nr_cpu_ids count of
+	possible CPUs for the booting hardware).
 
 	o	The numbers separated by the "/" are the qsmask followed
 		by the qsmaskinit.  The qsmask will have one bit
-		set for each entity in the next lower level that
-		has not yet checked in for the current grace period.
+		set for each entity in the next lower level that has
+		not yet checked in for the current grace period ("e"