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 biggest RCU changes in this cycle were:

   - Convert RCU's BUG_ON() and similar calls to WARN_ON() and similar.

   - Replace calls of RCU-bh and RCU-sched update-side functions to
     their vanilla RCU counterparts. This series is a step towards
     complete removal of the RCU-bh and RCU-sched update-side functions.

     ( Note that some of these conversions are going upstream via their
       respective maintainers. )

   - Documentation updates, including a number of flavor-consolidation
     updates from Joel Fernandes.

   - Miscellaneous fixes.

   - Automate generation of the initrd filesystem used for rcutorture
     testing.

   - Convert spin_is_locked() assertions to instead use lockdep.

     ( Note that some of these conversions are going upstream via their
       respective maintainers. )

   - SRCU updates, especially including a fix from Dennis Krein for a
     bag-on-head-class bug.

   - RCU torture-test updates"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (112 commits)
  rcutorture: Don't do busted forward-progress testing
  rcutorture: Use 100ms buckets for forward-progress callback histograms
  rcutorture: Recover from OOM during forward-progress tests
  rcutorture: Print forward-progress test age upon failure
  rcutorture: Print time since GP end upon forward-progress failure
  rcutorture: Print histogram of CB invocation at OOM time
  rcutorture: Print GP age upon forward-progress failure
  rcu: Print per-CPU callback counts for forward-progress failures
  rcu: Account for nocb-CPU callback counts in RCU CPU stall warnings
  rcutorture: Dump grace-period diagnostics upon forward-progress OOM
  rcutorture: Prepare for asynchronous access to rcu_fwd_startat
  torture: Remove unnecessary "ret" variables
  rcutorture: Affinity forward-progress test to avoid housekeeping CPUs
  rcutorture: Break up too-long rcu_torture_fwd_prog() function
  rcutorture: Remove cbflood facility
  torture: Bring any extra CPUs online during kernel startup
  rcutorture: Add call_rcu() flooding forward-progress tests
  rcutorture/formal: Replace synchronize_sched() with synchronize_rcu()
  tools/kernel.h: Replace synchronize_sched() with synchronize_rcu()
  net/decnet: Replace rcu_barrier_bh() with rcu_barrier()
  ...

Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.html

@@ -160,9 +160,9 @@ was in flight.
 If the CPU is idle, then <tt>sync_sched_exp_handler()</tt> reports
 the quiescent state.
 
-<p>
-Otherwise, the handler invokes <tt>resched_cpu()</tt>, which forces
-a future context switch.
+<p> Otherwise, the handler forces a future context switch by setting the
+NEED_RESCHED flag of the current task's thread flag and the CPU preempt
+counter.
 At the time of the context switch, the CPU reports the quiescent state.
 Should the CPU go offline first, it will report the quiescent state
 at that time.

Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html

@@ -77,7 +77,7 @@ The key point is that the lock-acquisition functions, including
 <tt>smp_mb__after_unlock_lock()</tt> immediately after successful
 acquisition of the lock.
 
-<p>Therefore, for any given <tt>rcu_node</tt> struction, any access
+<p>Therefore, for any given <tt>rcu_node</tt> structure, any access
 happening before one of the above lock-release functions will be seen
 by all CPUs as happening before any access happening after a later
 one of the above lock-acquisition functions.

Documentation/RCU/checklist.txt

@@ -63,7 +63,7 @@ over a rather long period of time, but improvements are always welcome!
 	pointer must be covered by rcu_read_lock(), rcu_read_lock_bh(),
 	rcu_read_lock_sched(), or by the appropriate update-side lock.
 	Disabling of preemption can serve as rcu_read_lock_sched(), but
-	is less readable.
+	is less readable and prevents lockdep from detecting locking issues.
 
 	Letting RCU-protected pointers "leak" out of an RCU read-side
 	critical section is every bid as bad as letting them leak out
@@ -285,11 +285,7 @@ over a rather long period of time, but improvements are always welcome!
 		here is that superuser already has lots of ways to crash
 		the machine.
 
-	d.	Use call_rcu_bh() rather than call_rcu(), in order to take
-		advantage of call_rcu_bh()'s faster grace periods.  (This
-		is only a partial solution, though.)
-
-	e.	Periodically invoke synchronize_rcu(), permitting a limited
+	d.	Periodically invoke synchronize_rcu(), permitting a limited
 		number of updates per grace period.
 
 	The same cautions apply to call_rcu_bh(), call_rcu_sched(),
@@ -324,37 +320,14 @@ over a rather long period of time, but improvements are always welcome!
 	will break Alpha, cause aggressive compilers to generate bad code,
 	and confuse people trying to read your code.
 
-11.	Note that synchronize_rcu() -only- guarantees to wait until
-	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 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
-	disabling where it should be using rcu_read_lock() will break
-	in CONFIG_PREEMPT=y kernel builds.
-
-	If you want to wait for interrupt handlers, NMI handlers, and
-	code under the influence of preempt_disable(), you instead
-	need to use synchronize_irq() or synchronize_sched().
-
-	This same limitation also applies to synchronize_rcu_bh()
-	and synchronize_srcu(), as well as to the asynchronous and
-	expedited forms of the three primitives, namely call_rcu(),
-	call_rcu_bh(), call_srcu(), synchronize_rcu_expedited(),
-	synchronize_rcu_bh_expedited(), and synchronize_srcu_expedited().
-
-12.	Any lock acquired by an RCU callback must be acquired elsewhere
+11.	Any lock acquired by an RCU callback must be acquired elsewhere
 	with softirq disabled, e.g., via spin_lock_irqsave(),
 	spin_lock_bh(), etc.  Failing to disable irq on a given
 	acquisition of that lock will result in deadlock as soon as
 	the RCU softirq handler happens to run your RCU callback while
 	interrupting that acquisition's critical section.
 
-13.	RCU callbacks can be and are executed in parallel.  In many cases,
+12.	RCU callbacks can be and are executed in parallel.  In many cases,
 	the callback code simply wrappers around kfree(), so that this
 	is not an issue (or, more accurately, to the extent that it is
 	an issue, the memory-allocator locking handles it).  However,
@@ -370,7 +343,7 @@ over a rather long period of time, but improvements are always welcome!
 	not the case, a self-spawning RCU callback would prevent the
 	victim CPU from ever going offline.)
 
-14.	Unlike other forms of RCU, it -is- permissible to block in an
+13.	Unlike other forms of RCU, it -is- permissible to block in an
 	SRCU read-side critical section (demarked by srcu_read_lock()
 	and srcu_read_unlock()), hence the "SRCU": "sleepable RCU".
 	Please note that if you don't need to sleep in read-side critical
@@ -414,7 +387,7 @@ over a rather long period of time, but improvements are always welcome!
 	Note that rcu_dereference() and rcu_assign_pointer() relate to
 	SRCU just as they do to other forms of RCU.
 
-15.	The whole point of call_rcu(), synchronize_rcu(), and friends
+14.	The whole point of call_rcu(), synchronize_rcu(), and friends
 	is to wait until all pre-existing readers have finished before
 	carrying out some otherwise-destructive operation.  It is
 	therefore critically important to -first- remove any path
@@ -426,13 +399,13 @@ over a rather long period of time, but improvements are always welcome!
 	is the caller's responsibility to guarantee that any subsequent
 	readers will execute safely.
 
-16.	The various RCU read-side primitives do -not- necessarily contain
+15.	The various RCU read-side primitives do -not- necessarily contain
 	memory barriers.  You should therefore plan for the CPU
 	and the compiler to freely reorder code into and out of RCU
 	read-side critical sections.  It is the responsibility of the
 	RCU update-side primitives to deal with this.
 
-17.	Use CONFIG_PROVE_LOCKING, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and the
+16.	Use CONFIG_PROVE_LOCKING, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and the
 	__rcu sparse checks to validate your RCU code.	These can help
 	find problems as follows:
 
@@ -455,7 +428,7 @@ over a rather long period of time, but improvements are always welcome!
 	These debugging aids can help you find problems that are
 	otherwise extremely difficult to spot.
 
-18.	If you register a callback using call_rcu(), call_rcu_bh(),
+17.	If you register a callback using call_rcu(), call_rcu_bh(),
 	call_rcu_sched(), or call_srcu(), and pass in a function defined
 	within a loadable module, then it in necessary to wait for
 	all pending callbacks to be invoked after the last invocation
@@ -469,8 +442,8 @@ over a rather long period of time, but improvements are always welcome!
 	You instead need to use one of the barrier functions:
 
 	o	call_rcu() -> rcu_barrier()
-	o	call_rcu_bh() -> rcu_barrier_bh()
-	o	call_rcu_sched() -> rcu_barrier_sched()
+	o	call_rcu_bh() -> rcu_barrier()
+	o	call_rcu_sched() -> rcu_barrier()
 	o	call_srcu() -> srcu_barrier()
 
 	However, these barrier functions are absolutely -not- guaranteed

Documentation/RCU/stallwarn.txt

@@ -176,9 +176,8 @@ causing stalls, and that the stall was affecting RCU-sched.  This message
 will normally be followed by stack dumps for each CPU.  Please note that
 PREEMPT_RCU builds can be stalled by tasks as well as by CPUs, and that
 the tasks will be indicated by PID, for example, "P3421".  It is even
-possible for a rcu_preempt_state stall to be caused by both CPUs -and-
-tasks, in which case the offending CPUs and tasks will all be called
-out in the list.
+possible for an rcu_state stall to be caused by both CPUs -and- tasks,
+in which case the offending CPUs and tasks will all be called out in the list.
 
 CPU 2's "(3 GPs behind)" indicates that this CPU has not interacted with
 the RCU core for the past three grace periods.  In contrast, CPU 16's "(0
@@ -206,7 +205,7 @@ 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.
 
-The "fps=" shows the number of force-quiescent-state idle/offline
+The "fqs=" shows the number of force-quiescent-state idle/offline
 detection passes that the grace-period kthread has made across this
 CPU since the last time that this CPU noted the beginning of a grace
 period.

Documentation/RCU/whatisRCU.txt

@@ -266,7 +266,7 @@ rcu_dereference()
 	unnecessary overhead on Alpha CPUs.
 
 	Note that the value returned by rcu_dereference() is valid
-	only within the enclosing RCU read-side critical section.
+	only within the enclosing RCU read-side critical section [1].
 	For example, the following is -not- legal:
 
 		rcu_read_lock();
@@ -292,6 +292,19 @@ rcu_dereference()
 	typically used indirectly, via the _rcu list-manipulation
 	primitives, such as list_for_each_entry_rcu().
 
+	[1] The variant rcu_dereference_protected() can be used outside
+	of an RCU read-side critical section as long as the usage is
+	protected by locks acquired by the update-side code.  This variant
+	avoids the lockdep warning that would happen when using (for
+	example) rcu_dereference() without rcu_read_lock() protection.
+	Using rcu_dereference_protected() also has the advantage
+	of permitting compiler optimizations that rcu_dereference()
+	must prohibit.	The rcu_dereference_protected() variant takes
+	a lockdep expression to indicate which locks must be acquired
+	by the caller. If the indicated protection is not provided,
+	a lockdep splat is emitted.  See RCU/Design/Requirements.html
+	and the API's code comments for more details and example usage.
+
 The following diagram shows how each API communicates among the
 reader, updater, and reclaimer.
 
@@ -322,28 +335,27 @@ to their callers and (2) call_rcu() callbacks may be invoked.  Efficient
 implementations of the RCU infrastructure make heavy use of batching in
 order to amortize their overhead over many uses of the corresponding APIs.
 
-There are no fewer than three RCU mechanisms in the Linux kernel; the
-diagram above shows the first one, which is by far the most commonly used.
-The rcu_dereference() and rcu_assign_pointer() primitives are used for
-all three mechanisms, but different defer and protect primitives are
-used as follows:
-
-	Defer			Protect
+There are at least three flavors of RCU usage in the Linux kernel. The diagram
+above shows the most common one. On the updater side, the rcu_assign_pointer(),
+sychronize_rcu() and call_rcu() primitives used are the same for all three
+flavors. However for protection (on the reader side), the primitives used vary
+depending on the flavor:
 
-a.	synchronize_rcu()	rcu_read_lock() / rcu_read_unlock()
-	call_rcu()		rcu_dereference()
+a.	rcu_read_lock() / rcu_read_unlock()
+	rcu_dereference()
 
-b.	synchronize_rcu_bh()	rcu_read_lock_bh() / rcu_read_unlock_bh()
-	call_rcu_bh()		rcu_dereference_bh()
+b.	rcu_read_lock_bh() / rcu_read_unlock_bh()
+	local_bh_disable() / local_bh_enable()
+	rcu_dereference_bh()
 
-c.	synchronize_sched()	rcu_read_lock_sched() / rcu_read_unlock_sched()
-	call_rcu_sched()	preempt_disable() / preempt_enable()
+c.	rcu_read_lock_sched() / rcu_read_unlock_sched()
+	preempt_disable() / preempt_enable()
 	local_irq_save() / local_irq_restore()
 	hardirq enter / hardirq exit
 	NMI enter / NMI exit
 	rcu_dereference_sched()
 
-These three mechanisms are used as follows:
+These three flavors are used as follows:
 
 a.	RCU applied to normal data structures.
 
@@ -867,18 +879,20 @@ RCU:	Critical sections	Grace period		Barrier
 
 bh:	Critical sections	Grace period		Barrier
 
-	rcu_read_lock_bh	call_rcu_bh		rcu_barrier_bh
-	rcu_read_unlock_bh	synchronize_rcu_bh
-	rcu_dereference_bh	synchronize_rcu_bh_expedited
+	rcu_read_lock_bh	call_rcu		rcu_barrier
+	rcu_read_unlock_bh	synchronize_rcu
+	[local_bh_disable]	synchronize_rcu_expedited
+	[and friends]
+	rcu_dereference_bh
 	rcu_dereference_bh_check
 	rcu_dereference_bh_protected
 	rcu_read_lock_bh_held
 
 sched:	Critical sections	Grace period		Barrier
 
-	rcu_read_lock_sched	synchronize_sched	rcu_barrier_sched
-	rcu_read_unlock_sched	call_rcu_sched
-	[preempt_disable]	synchronize_sched_expedited
+	rcu_read_lock_sched	call_rcu		rcu_barrier
+	rcu_read_unlock_sched	synchronize_rcu
+	[preempt_disable]	synchronize_rcu_expedited
 	[and friends]
 	rcu_read_lock_sched_notrace
 	rcu_read_unlock_sched_notrace
@@ -890,8 +904,8 @@ sched:	Critical sections	Grace period		Barrier
 
 SRCU:	Critical sections	Grace period		Barrier
 
-	srcu_read_lock		synchronize_srcu	srcu_barrier
-	srcu_read_unlock	call_srcu
+	srcu_read_lock		call_srcu		srcu_barrier
+	srcu_read_unlock	synchronize_srcu
 	srcu_dereference	synchronize_srcu_expedited
 	srcu_dereference_check
 	srcu_read_lock_held
@@ -1034,7 +1048,7 @@ Answer:		Just as PREEMPT_RT permits preemption of spinlock
 		spinlocks blocking while in RCU read-side critical
 		sections.
 
-		Why the apparent inconsistency?  Because it is it
+		Why the apparent inconsistency?  Because it is
 		possible to use priority boosting to keep the RCU
 		grace periods short if need be (for example, if running
 		short of memory).  In contrast, if blocking waiting

Documentation/admin-guide/kernel-parameters.txt

@@ -3754,24 +3754,6 @@
 			in microseconds.  The default of zero says
 			no holdoff.
 
-	rcutorture.cbflood_inter_holdoff= [KNL]
-			Set holdoff time (jiffies) between successive
-			callback-flood tests.
-
-	rcutorture.cbflood_intra_holdoff= [KNL]
-			Set holdoff time (jiffies) between successive
-			bursts of callbacks within a given callback-flood
-			test.
-
-	rcutorture.cbflood_n_burst= [KNL]
-			Set the number of bursts making up a given
-			callback-flood test.  Set this to zero to
-			disable callback-flood testing.
-
-	rcutorture.cbflood_n_per_burst= [KNL]
-			Set the number of callbacks to be registered
-			in a given burst of a callback-flood test.
-
 	rcutorture.fqs_duration= [KNL]
 			Set duration of force_quiescent_state bursts
 			in microseconds.
@@ -3784,6 +3766,23 @@
 			Set wait time between force_quiescent_state bursts
 			in seconds.
 
+	rcutorture.fwd_progress= [KNL]
+			Enable RCU grace-period forward-progress testing
+			for the types of RCU supporting this notion.
+
+	rcutorture.fwd_progress_div= [KNL]
+			Specify the fraction of a CPU-stall-warning
+			period to do tight-loop forward-progress testing.
+
+	rcutorture.fwd_progress_holdoff= [KNL]
+			Number of seconds to wait between successive
+			forward-progress tests.
+
+	rcutorture.fwd_progress_need_resched= [KNL]
+			Enclose cond_resched() calls within checks for
+			need_resched() during tight-loop forward-progress
+			testing.
+
 	rcutorture.gp_cond= [KNL]
 			Use conditional/asynchronous update-side
 			primitives, if available.