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 changes in this cycle are:

   - RCU flavor consolidation cleanups and optmizations

   - Documentation updates

   - Miscellaneous fixes

   - SRCU updates

   - RCU-sync flavor consolidation

   - Torture-test updates

   - Linux-kernel memory-consistency-model updates, most notably the
     addition of plain C-language accesses"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (61 commits)
  tools/memory-model: Improve data-race detection
  tools/memory-model: Change definition of rcu-fence
  tools/memory-model: Expand definition of barrier
  tools/memory-model: Do not use "herd" to refer to "herd7"
  tools/memory-model: Fix comment in MP+poonceonces.litmus
  Documentation: atomic_t.txt: Explain ordering provided by smp_mb__{before,after}_atomic()
  rcu: Don't return a value from rcu_assign_pointer()
  rcu: Force inlining of rcu_read_lock()
  rcu: Fix irritating whitespace error in rcu_assign_pointer()
  rcu: Upgrade sync_exp_work_done() to smp_mb()
  rcutorture: Upper case solves the case of the vanishing NULL pointer
  torture: Suppress propagating trace_printk() warning
  rcutorture: Dump trace buffer for callback pipe drain failures
  torture: Add --trust-make to suppress "make clean"
  torture: Make --cpus override idleness calculations
  torture: Run kernel build in source directory
  torture: Add function graph-tracing cheat sheet
  torture: Capture qemu output
  rcutorture: Tweak kvm options
  rcutorture: Add trivial RCU implementation
  ...

8 files changed, 47 insertions, 13 deletions

diff --git a/Documentation/RCU/rcuref.txt b/Documentation/RCU/rcuref.txt
index 613033ff2b9b..5e6429d66c24 100644
--- a/Documentation/RCU/rcuref.txt
+++ b/Documentation/RCU/rcuref.txt
@@ -12,6 +12,7 @@ please read on.
 Reference counting on elements of lists which are protected by traditional
 reader/writer spinlocks or semaphores are straightforward:
 
+CODE LISTING A:
 1.				2.
 add()				search_and_reference()
 {				{
@@ -28,7 +29,8 @@ add()				search_and_reference()
 release_referenced()			delete()
 {					{
     ...					    write_lock(&list_lock);
-    atomic_dec(&el->rc, relfunc)	    ...
+    if(atomic_dec_and_test(&el->rc))	    ...
+	kfree(el);
     ...					    remove_element
 }					    write_unlock(&list_lock);
  					    ...
@@ -44,6 +46,7 @@ search_and_reference() could potentially hold reference to an element which
 has already been deleted from the list/array.  Use atomic_inc_not_zero()
 in this scenario as follows:
 
+CODE LISTING B:
 1.					2.
 add()					search_and_reference()
 {					{
@@ -79,6 +82,7 @@ search_and_reference() code path.  In such cases, the
 atomic_dec_and_test() may be moved from delete() to el_free()
 as follows:
 
+CODE LISTING C:
 1.					2.
 add()					search_and_reference()
 {					{
@@ -114,6 +118,17 @@ 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.
 
+A clear advantage of the RCU-based pattern in listing C over the one
+in listing B is that any call to search_and_reference() that locates
+a given object will succeed in obtaining a reference to that object,
+even given a concurrent invocation of delete() for that same object.
+Similarly, a clear advantage of both listings B and C over listing A is
+that a call to delete() is not delayed even if there are an arbitrarily
+large number of calls to search_and_reference() searching for the same
+object that delete() was invoked on.  Instead, all that is delayed is
+the eventual invocation of kfree(), which is usually not a problem on
+modern computer systems, even the small ones.
+
 In cases where delete() can sleep, synchronize_rcu() can be called from
 delete(), so that el_free() can be subsumed into delete as follows:
 
@@ -130,3 +145,7 @@ delete()
     	kfree(el);
     ...
 }
+
+As additional examples in the kernel, the pattern in listing C is used by
+reference counting of struct pid, while the pattern in listing B is used by
+struct posix_acl.
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index 1ab70c37921f..13e88fc00f01 100644
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -153,7 +153,7 @@ rcupdate.rcu_task_stall_timeout
 	This boot/sysfs parameter controls the RCU-tasks stall warning
 	interval.  A value of zero or less suppresses RCU-tasks stall
 	warnings.  A positive value sets the stall-warning interval
-	in jiffies.  An RCU-tasks stall warning starts with the line:
+	in seconds.  An RCU-tasks stall warning starts with the line:
 
 		INFO: rcu_tasks detected stalls on tasks:
 
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 981651a8b65d..7e1a8721637a 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -212,7 +212,7 @@ synchronize_rcu()
 
 rcu_assign_pointer()
 
-	typeof(p) rcu_assign_pointer(p, typeof(p) v);
+	void rcu_assign_pointer(p, typeof(p) v);
 
 	Yes, rcu_assign_pointer() -is- implemented as a macro, though it
 	would be cool to be able to declare a function in this manner.
@@ -220,9 +220,9 @@ rcu_assign_pointer()
 
 	The updater uses this function to assign a new value to an
 	RCU-protected pointer, in order to safely communicate the change
-	in value from the updater to the reader.  This function returns
-	the new value, and also executes any memory-barrier instructions
-	required for a given CPU architecture.
+	in value from the updater to the reader.  This macro does not
+	evaluate to an rvalue, but it does execute any memory-barrier
+	instructions required for a given CPU architecture.
 
 	Perhaps just as important, it serves to document (1) which
 	pointers are protected by RCU and (2) the point at which a
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 5c7a0f5b0a2f..e6e806285703 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3752,6 +3752,12 @@
 			the propagation of recent CPU-hotplug changes up
 			the rcu_node combining tree.
 
+	rcutree.use_softirq=	[KNL]
+			If set to zero, move all RCU_SOFTIRQ processing to
+			per-CPU rcuc kthreads.  Defaults to a non-zero
+			value, meaning that RCU_SOFTIRQ is used by default.
+			Specify rcutree.use_softirq=0 to use rcuc kthreads.
+
 	rcutree.rcu_fanout_exact= [KNL]
 			Disable autobalancing of the rcu_node combining
 			tree.  This is used by rcutorture, and might
diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
index dca3fb0554db..b3afe69d03a1 100644
--- a/Documentation/atomic_t.txt
+++ b/Documentation/atomic_t.txt
@@ -187,8 +187,14 @@ The barriers:
 
   smp_mb__{before,after}_atomic()
 
-only apply to the RMW ops and can be used to augment/upgrade the ordering
-inherent to the used atomic op. These barriers provide a full smp_mb().
+only apply to the RMW atomic ops and can be used to augment/upgrade the
+ordering inherent to the op. These barriers act almost like a full smp_mb():
+smp_mb__before_atomic() orders all earlier accesses against the RMW op
+itself and all accesses following it, and smp_mb__after_atomic() orders all
+later accesses against the RMW op and all accesses preceding it. However,
+accesses between the smp_mb__{before,after}_atomic() and the RMW op are not
+ordered, so it is advisable to place the barrier right next to the RMW atomic
+op whenever possible.
 
 These helper barriers exist because architectures have varying implicit
 ordering on their SMP atomic primitives. For example our TSO architectures
@@ -212,7 +218,9 @@ Further, while something like:
   atomic_dec(&X);
 
 is a 'typical' RELEASE pattern, the barrier is strictly stronger than
-a RELEASE. Similarly for something like:
+a RELEASE because it orders preceding instructions against both the read
+and write parts of the atomic_dec(), and against all following instructions
+as well. Similarly, something like:
 
   atomic_inc(&X);
   smp_mb__after_atomic();
@@ -244,7 +252,8 @@ strictly stronger than ACQUIRE. As illustrated:
 
 This should not happen; but a hypothetical atomic_inc_acquire() --
 (void)atomic_fetch_inc_acquire() for instance -- would allow the outcome,
-since then:
+because it would not order the W part of the RMW against the following
+WRITE_ONCE.  Thus:
 
   P1			P2
 
diff --git a/Documentation/core-api/circular-buffers.rst b/Documentation/core-api/circular-buffers.rst
index 53e51caa3347..50966f66e398 100644
--- a/Documentation/core-api/circular-buffers.rst
+++ b/Documentation/core-api/circular-buffers.rst
@@ -3,7 +3,7 @@ Circular Buffers
 ================
 
 :Author: David Howells <dhowells@redhat.com>
-:Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+:Author: Paul E. McKenney <paulmck@linux.ibm.com>
 
 
 Linux provides a number of features that can be used to implement circular
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index f70ebcdfe592..e4e07c8ab89e 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -3,7 +3,7 @@
 			 ============================
 
 By: David Howells <dhowells@redhat.com>
-    Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+    Paul E. McKenney <paulmck@linux.ibm.com>
     Will Deacon <will.deacon@arm.com>
     Peter Zijlstra <peterz@infradead.org>
 
diff --git a/Documentation/translations/ko_KR/memory-barriers.txt b/Documentation/translations/ko_KR/memory-barriers.txt
index db0b9d8619f1..5f3c74dcad43 100644
--- a/Documentation/translations/ko_KR/memory-barriers.txt
+++ b/Documentation/translations/ko_KR/memory-barriers.txt
@@ -24,7 +24,7 @@ Documentation/memory-barriers.txt
 			 =========================
 
 저자: David Howells <dhowells@redhat.com>
-      Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+      Paul E. McKenney <paulmck@linux.ibm.com>
       Will Deacon <will.deacon@arm.com>
       Peter Zijlstra <peterz@infradead.org>