[PATCH 0/9] Apply new rest conversion patches to /dev branch

[PATCH 0/9] Apply new rest conversion patches to /dev branch

[Joel Fernandes (Google)]

This series fixes the rcu/dev branch so it can apply the new ReST conversion patches.

Patches based on "00ec8f46465e  rcu/nohz: Make multi_cpu_stop() enable tick on
all online CPUs"

The easiest was to do this is to revert the patches that conflict and then
applying the doc patches, and then applying them again. But in the
re-application, we convert the documentation

No manual fix ups were done in this process, other than to documentation.

thanks,

 - Joel

And in the process I learnt about get_user() and compiler barriers ;-)

Joel Fernandes (Google) (8):
Revert "rcu: Restore barrier() to rcu_read_lock() and
rcu_read_unlock()"
Revert "rcu: Add support for consolidated-RCU reader checking"
Revert "treewide: Rename rcu_dereference_raw_notrace() to _check()"
docs: rcu: Correct links referring to titles
docs: rcu: Increase toctree to 3
Revert "Revert "treewide: Rename rcu_dereference_raw_notrace() to
_check()""
Revert "Revert "rcu: Add support for consolidated-RCU reader
checking""
Revert "Revert "rcu: Restore barrier() to rcu_read_lock() and
rcu_read_unlock()""

Mauro Carvalho Chehab (1):
docs: rcu: convert some articles from html to ReST

.../Data-Structures/Data-Structures.html      | 1391 -------
.../Data-Structures/Data-Structures.rst       | 1163 ++++++
.../Expedited-Grace-Periods.html              |  668 ----
.../Expedited-Grace-Periods.rst               |  521 +++
.../Memory-Ordering/Tree-RCU-Diagram.html     |    9 -
.../Tree-RCU-Memory-Ordering.html             |  704 ----
.../Tree-RCU-Memory-Ordering.rst              |  624 +++
.../RCU/Design/Requirements/Requirements.html | 3401 -----------------
.../RCU/Design/Requirements/Requirements.rst  | 2704 +++++++++++++
Documentation/RCU/index.rst                   |    7 +-
Documentation/RCU/whatisRCU.txt               |    4 +-
11 files changed, 5020 insertions(+), 6176 deletions(-)
delete mode 100644 Documentation/RCU/Design/Data-Structures/Data-Structures.html
create mode 100644 Documentation/RCU/Design/Data-Structures/Data-Structures.rst
delete mode 100644 Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.html
create mode 100644 Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst
delete mode 100644 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Diagram.html
delete mode 100644 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html
create mode 100644 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
delete mode 100644 Documentation/RCU/Design/Requirements/Requirements.html
create mode 100644 Documentation/RCU/Design/Requirements/Requirements.rst

--
2.22.0.770.g0f2c4a37fd-goog

[PATCH 1/9] Revert "rcu: Restore barrier() to rcu_read_lock() and rcu_read_unlock()"

[Joel Fernandes (Google)]

This reverts commit d6b9cd7dc8e041ee83cb1362fce59a3cdb1f2709.
---
 .../RCU/Design/Requirements/Requirements.html | 71 -------------------
 kernel/rcu/tree_plugin.h                      | 11 +++
 2 files changed, 11 insertions(+), 71 deletions(-)

diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html
index 467251f7fef6..bdbc84f1b949 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.html
+++ b/Documentation/RCU/Design/Requirements/Requirements.html
@@ -2129,8 +2129,6 @@ Some of the relevant points of interest are as follows:
 <li>	<a href="#Hotplug CPU">Hotplug CPU</a>.
 <li>	<a href="#Scheduler and RCU">Scheduler and RCU</a>.
 <li>	<a href="#Tracing and RCU">Tracing and RCU</a>.
-<li>	<a href="#Accesses to User Memory and RCU">
-Accesses to User Memory and RCU</a>.
 <li>	<a href="#Energy Efficiency">Energy Efficiency</a>.
 <li>	<a href="#Scheduling-Clock Interrupts and RCU">
 	Scheduling-Clock Interrupts and RCU</a>.
@@ -2523,75 +2521,6 @@ cannot be used.
 The tracing folks both located the requirement and provided the
 needed fix, so this surprise requirement was relatively painless.
 
-<h3><a name="Accesses to User Memory and RCU">
-Accesses to User Memory and RCU</a></h3>
-
-<p>
-The kernel needs to access user-space memory, for example, to access
-data referenced by system-call parameters.
-The <tt>get_user()</tt> macro does this job.
-
-<p>
-However, user-space memory might well be paged out, which means
-that <tt>get_user()</tt> might well page-fault and thus block while
-waiting for the resulting I/O to complete.
-It would be a very bad thing for the compiler to reorder
-a <tt>get_user()</tt> invocation into an RCU read-side critical
-section.
-For example, suppose that the source code looked like this:
-
-<blockquote>
-<pre>
- 1 rcu_read_lock();
- 2 p = rcu_dereference(gp);
- 3 v = p-&gt;value;
- 4 rcu_read_unlock();
- 5 get_user(user_v, user_p);
- 6 do_something_with(v, user_v);
-</pre>
-</blockquote>
-
-<p>
-The compiler must not be permitted to transform this source code into
-the following:
-
-<blockquote>
-<pre>
- 1 rcu_read_lock();
- 2 p = rcu_dereference(gp);
- 3 get_user(user_v, user_p); // BUG: POSSIBLE PAGE FAULT!!!
- 4 v = p-&gt;value;
- 5 rcu_read_unlock();
- 6 do_something_with(v, user_v);
-</pre>
-</blockquote>
-
-<p>
-If the compiler did make this transformation in a
-<tt>CONFIG_PREEMPT=n</tt> kernel build, and if <tt>get_user()</tt> did
-page fault, the result would be a quiescent state in the middle
-of an RCU read-side critical section.
-This misplaced quiescent state could result in line&nbsp;4 being
-a use-after-free access, which could be bad for your kernel's
-actuarial statistics.
-Similar examples can be constructed with the call to <tt>get_user()</tt>
-preceding the <tt>rcu_read_lock()</tt>.
-
-<p>
-Unfortunately, <tt>get_user()</tt> doesn't have any particular
-ordering properties, and in some architectures the underlying <tt>asm</tt>
-isn't even marked <tt>volatile</tt>.
-And even if it was marked <tt>volatile</tt>, the above access to
-<tt>p-&gt;value</tt> is not volatile, so the compiler would not have any
-reason to keep those two accesses in order.
-
-<p>
-Therefore, the Linux-kernel definitions of <tt>rcu_read_lock()</tt>
-and <tt>rcu_read_unlock()</tt> must act as compiler barriers,
-at least for outermost instances of <tt>rcu_read_lock()</tt> and
-<tt>rcu_read_unlock()</tt> within a nested set of RCU read-side critical
-sections.
-
 <h3><a name="Energy Efficiency">Energy Efficiency</a></h3>
 
 <p>
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 379cb7e50a62..e1491d262892 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -288,6 +288,7 @@ void rcu_note_context_switch(bool preempt)
 	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 	struct rcu_node *rnp;
 
+	barrier(); /* Avoid RCU read-side critical sections leaking down. */
 	trace_rcu_utilization(TPS("Start context switch"));
 	lockdep_assert_irqs_disabled();
 	WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
@@ -330,6 +331,7 @@ void rcu_note_context_switch(bool preempt)
 	if (rdp->exp_deferred_qs)
 		rcu_report_exp_rdp(rdp);
 	trace_rcu_utilization(TPS("End context switch"));
+	barrier(); /* Avoid RCU read-side critical sections leaking up. */
 }
 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
 
@@ -813,6 +815,11 @@ static void rcu_qs(void)
  * dyntick-idle quiescent state visible to other CPUs, which will in
  * some cases serve for expedited as well as normal grace periods.
  * Either way, register a lightweight quiescent state.
+ *
+ * The barrier() calls are redundant in the common case when this is
+ * called externally, but just in case this is called from within this
+ * file.
+ *
  */
 void rcu_all_qs(void)
 {
@@ -827,12 +834,14 @@ void rcu_all_qs(void)
 		return;
 	}
 	this_cpu_write(rcu_data.rcu_urgent_qs, false);
+	barrier(); /* Avoid RCU read-side critical sections leaking down. */
 	if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) {
 		local_irq_save(flags);
 		rcu_momentary_dyntick_idle();
 		local_irq_restore(flags);
 	}
 	rcu_qs();
+	barrier(); /* Avoid RCU read-side critical sections leaking up. */
 	preempt_enable();
 }
 EXPORT_SYMBOL_GPL(rcu_all_qs);
@@ -842,6 +851,7 @@ EXPORT_SYMBOL_GPL(rcu_all_qs);
  */
 void rcu_note_context_switch(bool preempt)
 {
+	barrier(); /* Avoid RCU read-side critical sections leaking down. */
 	trace_rcu_utilization(TPS("Start context switch"));
 	rcu_qs();
 	/* Load rcu_urgent_qs before other flags. */
@@ -854,6 +864,7 @@ void rcu_note_context_switch(bool preempt)
 		rcu_tasks_qs(current);
 out:
 	trace_rcu_utilization(TPS("End context switch"));
+	barrier(); /* Avoid RCU read-side critical sections leaking up. */
 }
 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
 
-- 
2.22.0.770.g0f2c4a37fd-goog

[PATCH 2/9] Revert "rcu: Add support for consolidated-RCU reader checking"

[Joel Fernandes (Google)]

This reverts commit 50ad3f1f9b13c8a6f2ae79df4cecb2c21da1c7c8.
---
 include/linux/rculist.h  | 32 ++++----------------
 include/linux/rcupdate.h |  7 -----
 kernel/rcu/Kconfig.debug | 11 -------
 kernel/rcu/update.c      | 65 ++++++++++++++--------------------------
 4 files changed, 27 insertions(+), 88 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 4158b7212936..932296144131 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -40,24 +40,6 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
  */
 #define list_next_rcu(list)	(*((struct list_head __rcu **)(&(list)->next)))
 
-/*
- * Check during list traversal that we are within an RCU reader
- */
-
-#define check_arg_count_one(dummy)
-
-#ifdef CONFIG_PROVE_RCU_LIST
-#define __list_check_rcu(dummy, cond, extra...)				\
-	({								\
-	check_arg_count_one(extra);					\
-	RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(),		\
-			 "RCU-list traversed in non-reader section!");	\
-	 })
-#else
-#define __list_check_rcu(dummy, cond, extra...)				\
-	({ check_arg_count_one(extra); })
-#endif
-
 /*
  * Insert a new entry between two known consecutive entries.
  *
@@ -361,16 +343,14 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  * @pos:	the type * to use as a loop cursor.
  * @head:	the head for your list.
  * @member:	the name of the list_head within the struct.
- * @cond:	optional lockdep expression if called from non-RCU protection.
  *
  * This list-traversal primitive may safely run concurrently with
  * the _rcu list-mutation primitives such as list_add_rcu()
  * as long as the traversal is guarded by rcu_read_lock().
  */
-#define list_for_each_entry_rcu(pos, head, member, cond...)		\
-	for (__list_check_rcu(dummy, ## cond, 0),			\
-	     pos = list_entry_rcu((head)->next, typeof(*pos), member);	\
-		&pos->member != (head);					\
+#define list_for_each_entry_rcu(pos, head, member) \
+	for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
+		&pos->member != (head); \
 		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
 
 /**
@@ -636,15 +616,13 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
  * @pos:	the type * to use as a loop cursor.
  * @head:	the head for your list.
  * @member:	the name of the hlist_node within the struct.
- * @cond:	optional lockdep expression if called from non-RCU protection.
  *
  * This list-traversal primitive may safely run concurrently with
  * the _rcu list-mutation primitives such as hlist_add_head_rcu()
  * as long as the traversal is guarded by rcu_read_lock().
  */
-#define hlist_for_each_entry_rcu(pos, head, member, cond...)		\
-	for (__list_check_rcu(dummy, ## cond, 0),			\
-	     pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
+#define hlist_for_each_entry_rcu(pos, head, member)			\
+	for (pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
 			typeof(*(pos)), member);			\
 		pos;							\
 		pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 80d6056f5855..bfcafbc1e301 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -221,7 +221,6 @@ int debug_lockdep_rcu_enabled(void);
 int rcu_read_lock_held(void);
 int rcu_read_lock_bh_held(void);
 int rcu_read_lock_sched_held(void);
-int rcu_read_lock_any_held(void);
 
 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
@@ -242,12 +241,6 @@ static inline int rcu_read_lock_sched_held(void)
 {
 	return !preemptible();
 }
-
-static inline int rcu_read_lock_any_held(void)
-{
-	return !preemptible();
-}
-
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 #ifdef CONFIG_PROVE_RCU
diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 4aa02eee8f6c..5ec3ea4028e2 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -8,17 +8,6 @@ menu "RCU Debugging"
 config PROVE_RCU
 	def_bool PROVE_LOCKING
 
-config PROVE_RCU_LIST
-	bool "RCU list lockdep debugging"
-	depends on PROVE_RCU && RCU_EXPERT
-	default n
-	help
-	  Enable RCU lockdep checking for list usages. By default it is
-	  turned off since there are several list RCU users that still
-	  need to be converted to pass a lockdep expression. To prevent
-	  false-positive splats, we keep it default disabled but once all
-	  users are converted, we can remove this config option.
-
 config TORTURE_TEST
 	tristate
 	default n
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index c768f1fd6804..64e9cc8609e7 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -91,30 +91,19 @@ module_param(rcu_normal_after_boot, int, 0);
  * Similarly, we avoid claiming an SRCU read lock held if the current
  * CPU is offline.
  */
-static bool rcu_read_lock_held_common(bool *ret)
-{
-	if (!debug_lockdep_rcu_enabled()) {
-		*ret = 1;
-		return true;
-	}
-	if (!rcu_is_watching()) {
-		*ret = 0;
-		return true;
-	}
-	if (!rcu_lockdep_current_cpu_online()) {
-		*ret = 0;
-		return true;
-	}
-	return false;
-}
-
 int rcu_read_lock_sched_held(void)
 {
-	bool ret;
+	int lockdep_opinion = 0;
 
-	if (rcu_read_lock_held_common(&ret))
-		return ret;
-	return lock_is_held(&rcu_sched_lock_map) || !preemptible();
+	if (!debug_lockdep_rcu_enabled())
+		return 1;
+	if (!rcu_is_watching())
+		return 0;
+	if (!rcu_lockdep_current_cpu_online())
+		return 0;
+	if (debug_locks)
+		lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
+	return lockdep_opinion || !preemptible();
 }
 EXPORT_SYMBOL(rcu_read_lock_sched_held);
 #endif
@@ -271,10 +260,12 @@ NOKPROBE_SYMBOL(debug_lockdep_rcu_enabled);
  */
 int rcu_read_lock_held(void)
 {
-	bool ret;
-
-	if (rcu_read_lock_held_common(&ret))
-		return ret;
+	if (!debug_lockdep_rcu_enabled())
+		return 1;
+	if (!rcu_is_watching())
+		return 0;
+	if (!rcu_lockdep_current_cpu_online())
+		return 0;
 	return lock_is_held(&rcu_lock_map);
 }
 EXPORT_SYMBOL_GPL(rcu_read_lock_held);
@@ -296,28 +287,16 @@ EXPORT_SYMBOL_GPL(rcu_read_lock_held);
  */
 int rcu_read_lock_bh_held(void)
 {
-	bool ret;
-
-	if (rcu_read_lock_held_common(&ret))
-		return ret;
+	if (!debug_lockdep_rcu_enabled())
+		return 1;
+	if (!rcu_is_watching())
+		return 0;
+	if (!rcu_lockdep_current_cpu_online())
+		return 0;
 	return in_softirq() || irqs_disabled();
 }
 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 
-int rcu_read_lock_any_held(void)
-{
-	bool ret;
-
-	if (rcu_read_lock_held_common(&ret))
-		return ret;
-	if (lock_is_held(&rcu_lock_map) ||
-	    lock_is_held(&rcu_bh_lock_map) ||
-	    lock_is_held(&rcu_sched_lock_map))
-		return 1;
-	return !preemptible();
-}
-EXPORT_SYMBOL_GPL(rcu_read_lock_any_held);
-
 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 /**
-- 
2.22.0.770.g0f2c4a37fd-goog

[PATCH 3/9] Revert "treewide: Rename rcu_dereference_raw_notrace() to _check()"

[Joel Fernandes (Google)]

This reverts commit 355e9972da81e803bbb825b76106ae9b358caf8e.
---
 Documentation/RCU/Design/Requirements/Requirements.html | 2 +-
 arch/powerpc/include/asm/kvm_book3s_64.h                | 2 +-
 include/linux/rculist.h                                 | 6 +++---
 include/linux/rcupdate.h                                | 2 +-
 kernel/trace/ftrace_internal.h                          | 8 ++++----
 kernel/trace/trace.c                                    | 4 ++--
 6 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html
index bdbc84f1b949..5a9238a2883c 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.html
+++ b/Documentation/RCU/Design/Requirements/Requirements.html
@@ -2512,7 +2512,7 @@ disabled across the entire RCU read-side critical section.
 <p>
 It is possible to use tracing on RCU code, but tracing itself
 uses RCU.
-For this reason, <tt>rcu_dereference_raw_check()</tt>
+For this reason, <tt>rcu_dereference_raw_notrace()</tt>
 is provided for use by tracing, which avoids the destructive
 recursion that could otherwise ensue.
 This API is also used by virtualization in some architectures,
diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
index 04b2b927bb5a..bb7c8cc77f1a 100644
--- a/arch/powerpc/include/asm/kvm_book3s_64.h
+++ b/arch/powerpc/include/asm/kvm_book3s_64.h
@@ -535,7 +535,7 @@ static inline void note_hpte_modification(struct kvm *kvm,
  */
 static inline struct kvm_memslots *kvm_memslots_raw(struct kvm *kvm)
 {
-	return rcu_dereference_raw_check(kvm->memslots[0]);
+	return rcu_dereference_raw_notrace(kvm->memslots[0]);
 }
 
 extern void kvmppc_mmu_debugfs_init(struct kvm *kvm);
diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 932296144131..e91ec9ddcd30 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -622,7 +622,7 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
  * as long as the traversal is guarded by rcu_read_lock().
  */
 #define hlist_for_each_entry_rcu(pos, head, member)			\
-	for (pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
+	for (pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
 			typeof(*(pos)), member);			\
 		pos;							\
 		pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
@@ -642,10 +642,10 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
  * not do any RCU debugging or tracing.
  */
 #define hlist_for_each_entry_rcu_notrace(pos, head, member)			\
-	for (pos = hlist_entry_safe(rcu_dereference_raw_check(hlist_first_rcu(head)),\
+	for (pos = hlist_entry_safe (rcu_dereference_raw_notrace(hlist_first_rcu(head)),\
 			typeof(*(pos)), member);			\
 		pos;							\
-		pos = hlist_entry_safe(rcu_dereference_raw_check(hlist_next_rcu(\
+		pos = hlist_entry_safe(rcu_dereference_raw_notrace(hlist_next_rcu(\
 			&(pos)->member)), typeof(*(pos)), member))
 
 /**
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index bfcafbc1e301..8f7167478c1d 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -476,7 +476,7 @@ do {									      \
  * The no-tracing version of rcu_dereference_raw() must not call
  * rcu_read_lock_held().
  */
-#define rcu_dereference_raw_check(p) __rcu_dereference_check((p), 1, __rcu)
+#define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
 
 /**
  * rcu_dereference_protected() - fetch RCU pointer when updates prevented
diff --git a/kernel/trace/ftrace_internal.h b/kernel/trace/ftrace_internal.h
index 0456e0a3dab1..0515a2096f90 100644
--- a/kernel/trace/ftrace_internal.h
+++ b/kernel/trace/ftrace_internal.h
@@ -6,22 +6,22 @@
 
 /*
  * Traverse the ftrace_global_list, invoking all entries.  The reason that we
- * can use rcu_dereference_raw_check() is that elements removed from this list
+ * can use rcu_dereference_raw_notrace() is that elements removed from this list
  * are simply leaked, so there is no need to interact with a grace-period
- * mechanism.  The rcu_dereference_raw_check() calls are needed to handle
+ * mechanism.  The rcu_dereference_raw_notrace() calls are needed to handle
  * concurrent insertions into the ftrace_global_list.
  *
  * Silly Alpha and silly pointer-speculation compiler optimizations!
  */
 #define do_for_each_ftrace_op(op, list)			\
-	op = rcu_dereference_raw_check(list);			\
+	op = rcu_dereference_raw_notrace(list);			\
 	do
 
 /*
  * Optimized for just a single item in the list (as that is the normal case).
  */
 #define while_for_each_ftrace_op(op)				\
-	while (likely(op = rcu_dereference_raw_check((op)->next)) &&	\
+	while (likely(op = rcu_dereference_raw_notrace((op)->next)) &&	\
 	       unlikely((op) != &ftrace_list_end))
 
 extern struct ftrace_ops __rcu *ftrace_ops_list;
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 642474b26ba7..525a97fbbc60 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2642,10 +2642,10 @@ static void ftrace_exports(struct ring_buffer_event *event)
 
 	preempt_disable_notrace();
 
-	export = rcu_dereference_raw_check(ftrace_exports_list);
+	export = rcu_dereference_raw_notrace(ftrace_exports_list);
 	while (export) {
 		trace_process_export(export, event);
-		export = rcu_dereference_raw_check(export->next);
+		export = rcu_dereference_raw_notrace(export->next);
 	}
 
 	preempt_enable_notrace();
-- 
2.22.0.770.g0f2c4a37fd-goog

[PATCH 5/9] docs: rcu: Correct links referring to titles

[Joel Fernandes (Google)]

Mauro's auto conversion broken these links, fix them.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 .../Tree-RCU-Memory-Ordering.rst              | 17 ++--
 .../RCU/Design/Requirements/Requirements.rst  | 90 ++++++++-----------
 2 files changed, 47 insertions(+), 60 deletions(-)

diff --git a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
index 1011b5db1b3d..248b1222f918 100644
--- a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
+++ b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
@@ -230,15 +230,14 @@ Tree RCU Grace Period Memory Ordering Components
 Tree RCU's grace-period memory-ordering guarantee is provided by a
 number of RCU components:
 
-#. `Callback Registry <#Callback%20Registry>`__
-#. `Grace-Period Initialization <#Grace-Period%20Initialization>`__
-#. `Self-Reported Quiescent
-   States <#Self-Reported%20Quiescent%20States>`__
-#. `Dynamic Tick Interface <#Dynamic%20Tick%20Interface>`__
-#. `CPU-Hotplug Interface <#CPU-Hotplug%20Interface>`__
-#. `Forcing Quiescent States <Forcing%20Quiescent%20States>`__
-#. `Grace-Period Cleanup <Grace-Period%20Cleanup>`__
-#. `Callback Invocation <Callback%20Invocation>`__
+#. `Callback Registry`_
+#. `Grace-Period Initialization`_
+#. `Self-Reported Quiescent States`_
+#. `Dynamic Tick Interface`_
+#. `CPU-Hotplug Interface`_
+#. `Forcing Quiescent States`_
+#. `Grace-Period Cleanup`_
+#. `Callback Invocation`_
 
 Each of the following section looks at the corresponding component in
 detail.
diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
index 876e0038bb58..a33b5fb331b4 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.rst
+++ b/Documentation/RCU/Design/Requirements/Requirements.rst
@@ -36,16 +36,14 @@ technologies in interesting new ways.
 All that aside, here are the categories of currently known RCU
 requirements:
 
-#. `Fundamental Requirements <#Fundamental%20Requirements>`__
-#. `Fundamental Non-Requirements <#Fundamental%20Non-Requirements>`__
-#. `Parallelism Facts of Life <#Parallelism%20Facts%20of%20Life>`__
-#. `Quality-of-Implementation
-   Requirements <#Quality-of-Implementation%20Requirements>`__
-#. `Linux Kernel Complications <#Linux%20Kernel%20Complications>`__
-#. `Software-Engineering
-   Requirements <#Software-Engineering%20Requirements>`__
-#. `Other RCU Flavors <#Other%20RCU%20Flavors>`__
-#. `Possible Future Changes <#Possible%20Future%20Changes>`__
+#. `Fundamental Requirements`_
+#. `Fundamental Non-Requirements`_
+#. `Parallelism Facts of Life`_
+#. `Quality-of-Implementation Requirements`_
+#. `Linux Kernel Complications`_
+#. `Software-Engineering Requirements`_
+#. `Other RCU Flavors`_
+#. `Possible Future Changes`_
 
 This is followed by a `summary <#Summary>`__, however, the answers to
 each quick quiz immediately follows the quiz. Select the big white space
@@ -57,13 +55,11 @@ Fundamental Requirements
 RCU's fundamental requirements are the closest thing RCU has to hard
 mathematical requirements. These are:
 
-#. `Grace-Period Guarantee <#Grace-Period%20Guarantee>`__
-#. `Publish-Subscribe Guarantee <#Publish-Subscribe%20Guarantee>`__
-#. `Memory-Barrier Guarantees <#Memory-Barrier%20Guarantees>`__
-#. `RCU Primitives Guaranteed to Execute
-   Unconditionally <#RCU%20Primitives%20Guaranteed%20to%20Execute%20Unconditionally>`__
-#. `Guaranteed Read-to-Write
-   Upgrade <#Guaranteed%20Read-to-Write%20Upgrade>`__
+#. `Grace-Period Guarantee`_
+#. `Publish/Subscribe Guarantee`_
+#. `Memory-Barrier Guarantees`_
+#. `RCU Primitives Guaranteed to Execute Unconditionally`_
+#. `Guaranteed Read-to-Write Upgrade`_
 
 Grace-Period Guarantee
 ~~~~~~~~~~~~~~~~~~~~~~
@@ -689,16 +685,11 @@ infinitely long, however, the following sections list a few
 non-guarantees that have caused confusion. Except where otherwise noted,
 these non-guarantees were premeditated.
 
-#. `Readers Impose Minimal
-   Ordering <#Readers%20Impose%20Minimal%20Ordering>`__
-#. `Readers Do Not Exclude
-   Updaters <#Readers%20Do%20Not%20Exclude%20Updaters>`__
-#. `Updaters Only Wait For Old
-   Readers <#Updaters%20Only%20Wait%20For%20Old%20Readers>`__
-#. `Grace Periods Don't Partition Read-Side Critical
-   Sections <#Grace%20Periods%20Don't%20Partition%20Read-Side%20Critical%20Sections>`__
-#. `Read-Side Critical Sections Don't Partition Grace
-   Periods <#Read-Side%20Critical%20Sections%20Don't%20Partition%20Grace%20Periods>`__
+#. `Readers Impose Minimal Ordering`_
+#. `Readers Do Not Exclude Updaters`_
+#. `Updaters Only Wait For Old Readers`_
+#. `Grace Periods Don't Partition Read-Side Critical Sections`_
+#. `Read-Side Critical Sections Don't Partition Grace Periods`_
 
 Readers Impose Minimal Ordering
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -1056,11 +1047,11 @@ it would likely be subject to limitations that would make it
 inappropriate for industrial-strength production use. Classes of
 quality-of-implementation requirements are as follows:
 
-#. `Specialization <#Specialization>`__
-#. `Performance and Scalability <#Performance%20and%20Scalability>`__
-#. `Forward Progress <#Forward%20Progress>`__
-#. `Composability <#Composability>`__
-#. `Corner Cases <#Corner%20Cases>`__
+#. `Specialization`_
+#. `Performance and Scalability`_
+#. `Forward Progress`_
+#. `Composability`_
+#. `Corner Cases`_
 
 These classes is covered in the following sections.
 
@@ -1692,21 +1683,18 @@ The Linux kernel provides an interesting environment for all kinds of
 software, including RCU. Some of the relevant points of interest are as
 follows:
 
-#. `Configuration <#Configuration>`__.
-#. `Firmware Interface <#Firmware%20Interface>`__.
-#. `Early Boot <#Early%20Boot>`__.
-#. `Interrupts and non-maskable interrupts
-   (NMIs) <#Interrupts%20and%20NMIs>`__.
-#. `Loadable Modules <#Loadable%20Modules>`__.
-#. `Hotplug CPU <#Hotplug%20CPU>`__.
-#. `Scheduler and RCU <#Scheduler%20and%20RCU>`__.
-#. `Tracing and RCU <#Tracing%20and%20RCU>`__.
-#. `Energy Efficiency <#Energy%20Efficiency>`__.
-#. `Scheduling-Clock Interrupts and
-   RCU <#Scheduling-Clock%20Interrupts%20and%20RCU>`__.
-#. `Memory Efficiency <#Memory%20Efficiency>`__.
-#. `Performance, Scalability, Response Time, and
-   Reliability <#Performance,%20Scalability,%20Response%20Time,%20and%20Reliability>`__.
+#. `Configuration`_
+#. `Firmware Interface`_
+#. `Early Boot`_
+#. `Interrupts and NMIs`_
+#. `Loadable Modules`_
+#. `Hotplug CPU`_
+#. `Scheduler and RCU`_
+#. `Tracing and RCU`_
+#. `Energy Efficiency`_
+#. `Scheduling-Clock Interrupts and RCU`_
+#. `Memory Efficiency`_
+#. `Performance, Scalability, Response Time, and Reliability`_
 
 This list is probably incomplete, but it does give a feel for the most
 notable Linux-kernel complications. Each of the following sections
@@ -2344,10 +2332,10 @@ implementations, non-preemptible and preemptible. The other four flavors
 are listed below, with requirements for each described in a separate
 section.
 
-#. `Bottom-Half Flavor (Historical) <#Bottom-Half%20Flavor>`__
-#. `Sched Flavor (Historical) <#Sched%20Flavor>`__
-#. `Sleepable RCU <#Sleepable%20RCU>`__
-#. `Tasks RCU <#Tasks%20RCU>`__
+#. `Bottom-Half Flavor (Historical)`_
+#. `Sched Flavor (Historical)`_
+#. `Sleepable RCU`_
+#. `Tasks RCU`_
 
 Bottom-Half Flavor (Historical)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- 
2.22.0.770.g0f2c4a37fd-goog

[PATCH 6/9] docs: rcu: Increase toctree to 3

[Joel Fernandes (Google)]

These documents are long and have various sections. Provide a good
toc nesting level.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 Documentation/RCU/index.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/RCU/index.rst b/Documentation/RCU/index.rst
index 94427dc1f23d..5c99185710fa 100644
--- a/Documentation/RCU/index.rst
+++ b/Documentation/RCU/index.rst
@@ -5,7 +5,7 @@ RCU concepts
 ============
 
 .. toctree::
-   :maxdepth: 1
+   :maxdepth: 3
 
    rcu
    listRCU
-- 
2.22.0.770.g0f2c4a37fd-goog

[PATCH 7/9] Revert "Revert "treewide: Rename rcu_dereference_raw_notrace() to _check()""

[Joel Fernandes (Google)]

This reverts commit 61d814760f1d2dffdc8db636f70bbef07c30acd5.
---
 Documentation/RCU/Design/Requirements/Requirements.rst | 2 +-
 arch/powerpc/include/asm/kvm_book3s_64.h               | 2 +-
 include/linux/rculist.h                                | 6 +++---
 include/linux/rcupdate.h                               | 2 +-
 kernel/trace/ftrace_internal.h                         | 8 ++++----
 kernel/trace/trace.c                                   | 4 ++--
 6 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
index a33b5fb331b4..0b222469d7ce 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.rst
+++ b/Documentation/RCU/Design/Requirements/Requirements.rst
@@ -1997,7 +1997,7 @@ Tracing and RCU
 ~~~~~~~~~~~~~~~
 
 It is possible to use tracing on RCU code, but tracing itself uses RCU.
-For this reason, ``rcu_dereference_raw_notrace()`` is provided for use
+For this reason, ``rcu_dereference_raw_check()`` is provided for use
 by tracing, which avoids the destructive recursion that could otherwise
 ensue. This API is also used by virtualization in some architectures,
 where RCU readers execute in environments in which tracing cannot be
diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
index bb7c8cc77f1a..04b2b927bb5a 100644
--- a/arch/powerpc/include/asm/kvm_book3s_64.h
+++ b/arch/powerpc/include/asm/kvm_book3s_64.h
@@ -535,7 +535,7 @@ static inline void note_hpte_modification(struct kvm *kvm,
  */
 static inline struct kvm_memslots *kvm_memslots_raw(struct kvm *kvm)
 {
-	return rcu_dereference_raw_notrace(kvm->memslots[0]);
+	return rcu_dereference_raw_check(kvm->memslots[0]);
 }
 
 extern void kvmppc_mmu_debugfs_init(struct kvm *kvm);
diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index e91ec9ddcd30..932296144131 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -622,7 +622,7 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
  * as long as the traversal is guarded by rcu_read_lock().
  */
 #define hlist_for_each_entry_rcu(pos, head, member)			\
-	for (pos = hlist_entry_safe (rcu_dereference_raw(hlist_first_rcu(head)),\
+	for (pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
 			typeof(*(pos)), member);			\
 		pos;							\
 		pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
@@ -642,10 +642,10 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
  * not do any RCU debugging or tracing.
  */
 #define hlist_for_each_entry_rcu_notrace(pos, head, member)			\
-	for (pos = hlist_entry_safe (rcu_dereference_raw_notrace(hlist_first_rcu(head)),\
+	for (pos = hlist_entry_safe(rcu_dereference_raw_check(hlist_first_rcu(head)),\
 			typeof(*(pos)), member);			\
 		pos;							\
-		pos = hlist_entry_safe(rcu_dereference_raw_notrace(hlist_next_rcu(\
+		pos = hlist_entry_safe(rcu_dereference_raw_check(hlist_next_rcu(\
 			&(pos)->member)), typeof(*(pos)), member))
 
 /**
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 8f7167478c1d..bfcafbc1e301 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -476,7 +476,7 @@ do {									      \
  * The no-tracing version of rcu_dereference_raw() must not call
  * rcu_read_lock_held().
  */
-#define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
+#define rcu_dereference_raw_check(p) __rcu_dereference_check((p), 1, __rcu)
 
 /**
  * rcu_dereference_protected() - fetch RCU pointer when updates prevented
diff --git a/kernel/trace/ftrace_internal.h b/kernel/trace/ftrace_internal.h
index 0515a2096f90..0456e0a3dab1 100644
--- a/kernel/trace/ftrace_internal.h
+++ b/kernel/trace/ftrace_internal.h
@@ -6,22 +6,22 @@
 
 /*
  * Traverse the ftrace_global_list, invoking all entries.  The reason that we
- * can use rcu_dereference_raw_notrace() is that elements removed from this list
+ * can use rcu_dereference_raw_check() is that elements removed from this list
  * are simply leaked, so there is no need to interact with a grace-period
- * mechanism.  The rcu_dereference_raw_notrace() calls are needed to handle
+ * mechanism.  The rcu_dereference_raw_check() calls are needed to handle
  * concurrent insertions into the ftrace_global_list.
  *
  * Silly Alpha and silly pointer-speculation compiler optimizations!
  */
 #define do_for_each_ftrace_op(op, list)			\
-	op = rcu_dereference_raw_notrace(list);			\
+	op = rcu_dereference_raw_check(list);			\
 	do
 
 /*
  * Optimized for just a single item in the list (as that is the normal case).
  */
 #define while_for_each_ftrace_op(op)				\
-	while (likely(op = rcu_dereference_raw_notrace((op)->next)) &&	\
+	while (likely(op = rcu_dereference_raw_check((op)->next)) &&	\
 	       unlikely((op) != &ftrace_list_end))
 
 extern struct ftrace_ops __rcu *ftrace_ops_list;
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 525a97fbbc60..642474b26ba7 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2642,10 +2642,10 @@ static void ftrace_exports(struct ring_buffer_event *event)
 
 	preempt_disable_notrace();
 
-	export = rcu_dereference_raw_notrace(ftrace_exports_list);
+	export = rcu_dereference_raw_check(ftrace_exports_list);
 	while (export) {
 		trace_process_export(export, event);
-		export = rcu_dereference_raw_notrace(export->next);
+		export = rcu_dereference_raw_check(export->next);
 	}
 
 	preempt_enable_notrace();
-- 
2.22.0.770.g0f2c4a37fd-goog

[PATCH 8/9] Revert "Revert "rcu: Add support for consolidated-RCU reader checking""

[Joel Fernandes (Google)]

This reverts commit 24be1727c524b5874d5dc7828cd392cf86c3341e.
---
 include/linux/rculist.h  | 32 ++++++++++++++++----
 include/linux/rcupdate.h |  7 +++++
 kernel/rcu/Kconfig.debug | 11 +++++++
 kernel/rcu/update.c      | 65 ++++++++++++++++++++++++++--------------
 4 files changed, 88 insertions(+), 27 deletions(-)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 932296144131..4158b7212936 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -40,6 +40,24 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
  */
 #define list_next_rcu(list)	(*((struct list_head __rcu **)(&(list)->next)))
 
+/*
+ * Check during list traversal that we are within an RCU reader
+ */
+
+#define check_arg_count_one(dummy)
+
+#ifdef CONFIG_PROVE_RCU_LIST
+#define __list_check_rcu(dummy, cond, extra...)				\
+	({								\
+	check_arg_count_one(extra);					\
+	RCU_LOCKDEP_WARN(!cond && !rcu_read_lock_any_held(),		\
+			 "RCU-list traversed in non-reader section!");	\
+	 })
+#else
+#define __list_check_rcu(dummy, cond, extra...)				\
+	({ check_arg_count_one(extra); })
+#endif
+
 /*
  * Insert a new entry between two known consecutive entries.
  *
@@ -343,14 +361,16 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
  * @pos:	the type * to use as a loop cursor.
  * @head:	the head for your list.
  * @member:	the name of the list_head within the struct.
+ * @cond:	optional lockdep expression if called from non-RCU protection.
  *
  * This list-traversal primitive may safely run concurrently with
  * the _rcu list-mutation primitives such as list_add_rcu()
  * as long as the traversal is guarded by rcu_read_lock().
  */
-#define list_for_each_entry_rcu(pos, head, member) \
-	for (pos = list_entry_rcu((head)->next, typeof(*pos), member); \
-		&pos->member != (head); \
+#define list_for_each_entry_rcu(pos, head, member, cond...)		\
+	for (__list_check_rcu(dummy, ## cond, 0),			\
+	     pos = list_entry_rcu((head)->next, typeof(*pos), member);	\
+		&pos->member != (head);					\
 		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
 
 /**
@@ -616,13 +636,15 @@ static inline void hlist_add_behind_rcu(struct hlist_node *n,
  * @pos:	the type * to use as a loop cursor.
  * @head:	the head for your list.
  * @member:	the name of the hlist_node within the struct.
+ * @cond:	optional lockdep expression if called from non-RCU protection.
  *
  * This list-traversal primitive may safely run concurrently with
  * the _rcu list-mutation primitives such as hlist_add_head_rcu()
  * as long as the traversal is guarded by rcu_read_lock().
  */
-#define hlist_for_each_entry_rcu(pos, head, member)			\
-	for (pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
+#define hlist_for_each_entry_rcu(pos, head, member, cond...)		\
+	for (__list_check_rcu(dummy, ## cond, 0),			\
+	     pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
 			typeof(*(pos)), member);			\
 		pos;							\
 		pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index bfcafbc1e301..80d6056f5855 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -221,6 +221,7 @@ int debug_lockdep_rcu_enabled(void);
 int rcu_read_lock_held(void);
 int rcu_read_lock_bh_held(void);
 int rcu_read_lock_sched_held(void);
+int rcu_read_lock_any_held(void);
 
 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
@@ -241,6 +242,12 @@ static inline int rcu_read_lock_sched_held(void)
 {
 	return !preemptible();
 }
+
+static inline int rcu_read_lock_any_held(void)
+{
+	return !preemptible();
+}
+
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 #ifdef CONFIG_PROVE_RCU
diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 5ec3ea4028e2..4aa02eee8f6c 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -8,6 +8,17 @@ menu "RCU Debugging"
 config PROVE_RCU
 	def_bool PROVE_LOCKING
 
+config PROVE_RCU_LIST
+	bool "RCU list lockdep debugging"
+	depends on PROVE_RCU && RCU_EXPERT
+	default n
+	help
+	  Enable RCU lockdep checking for list usages. By default it is
+	  turned off since there are several list RCU users that still
+	  need to be converted to pass a lockdep expression. To prevent
+	  false-positive splats, we keep it default disabled but once all
+	  users are converted, we can remove this config option.
+
 config TORTURE_TEST
 	tristate
 	default n
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 64e9cc8609e7..c768f1fd6804 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -91,19 +91,30 @@ module_param(rcu_normal_after_boot, int, 0);
  * Similarly, we avoid claiming an SRCU read lock held if the current
  * CPU is offline.
  */
+static bool rcu_read_lock_held_common(bool *ret)
+{
+	if (!debug_lockdep_rcu_enabled()) {
+		*ret = 1;
+		return true;
+	}
+	if (!rcu_is_watching()) {
+		*ret = 0;
+		return true;
+	}
+	if (!rcu_lockdep_current_cpu_online()) {
+		*ret = 0;
+		return true;
+	}
+	return false;
+}
+
 int rcu_read_lock_sched_held(void)
 {
-	int lockdep_opinion = 0;
+	bool ret;
 
-	if (!debug_lockdep_rcu_enabled())
-		return 1;
-	if (!rcu_is_watching())
-		return 0;
-	if (!rcu_lockdep_current_cpu_online())
-		return 0;
-	if (debug_locks)
-		lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
-	return lockdep_opinion || !preemptible();
+	if (rcu_read_lock_held_common(&ret))
+		return ret;
+	return lock_is_held(&rcu_sched_lock_map) || !preemptible();
 }
 EXPORT_SYMBOL(rcu_read_lock_sched_held);
 #endif
@@ -260,12 +271,10 @@ NOKPROBE_SYMBOL(debug_lockdep_rcu_enabled);
  */
 int rcu_read_lock_held(void)
 {
-	if (!debug_lockdep_rcu_enabled())
-		return 1;
-	if (!rcu_is_watching())
-		return 0;
-	if (!rcu_lockdep_current_cpu_online())
-		return 0;
+	bool ret;
+
+	if (rcu_read_lock_held_common(&ret))
+		return ret;
 	return lock_is_held(&rcu_lock_map);
 }
 EXPORT_SYMBOL_GPL(rcu_read_lock_held);
@@ -287,16 +296,28 @@ EXPORT_SYMBOL_GPL(rcu_read_lock_held);
  */
 int rcu_read_lock_bh_held(void)
 {
-	if (!debug_lockdep_rcu_enabled())
-		return 1;
-	if (!rcu_is_watching())
-		return 0;
-	if (!rcu_lockdep_current_cpu_online())
-		return 0;
+	bool ret;
+
+	if (rcu_read_lock_held_common(&ret))
+		return ret;
 	return in_softirq() || irqs_disabled();
 }
 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 
+int rcu_read_lock_any_held(void)
+{
+	bool ret;
+
+	if (rcu_read_lock_held_common(&ret))
+		return ret;
+	if (lock_is_held(&rcu_lock_map) ||
+	    lock_is_held(&rcu_bh_lock_map) ||
+	    lock_is_held(&rcu_sched_lock_map))
+		return 1;
+	return !preemptible();
+}
+EXPORT_SYMBOL_GPL(rcu_read_lock_any_held);
+
 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 /**
-- 
2.22.0.770.g0f2c4a37fd-goog

[PATCH 9/9] Revert "Revert "rcu: Restore barrier() to rcu_read_lock() and rcu_read_unlock()""

[Joel Fernandes (Google)]

This reverts commit 43ddb98ebe7171ff1c6e11c1616fd03726d8e9bf while
adding the documentation that the original commit added but in ReST
format.
---
 .../RCU/Design/Requirements/Requirements.rst  | 54 +++++++++++++++++++
 kernel/rcu/tree_plugin.h                      | 11 ----
 2 files changed, 54 insertions(+), 11 deletions(-)

diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
index 0b222469d7ce..fd5e2cbc4935 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.rst
+++ b/Documentation/RCU/Design/Requirements/Requirements.rst
@@ -1691,6 +1691,7 @@ follows:
 #. `Hotplug CPU`_
 #. `Scheduler and RCU`_
 #. `Tracing and RCU`_
+#. `Accesses to User Memory and RCU`_
 #. `Energy Efficiency`_
 #. `Scheduling-Clock Interrupts and RCU`_
 #. `Memory Efficiency`_
@@ -2004,6 +2005,59 @@ where RCU readers execute in environments in which tracing cannot be
 used. The tracing folks both located the requirement and provided the
 needed fix, so this surprise requirement was relatively painless.
 
+Accesses to User Memory and RCU
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The kernel needs to access user-space memory, for example, to access data
+referenced by system-call parameters.  The ``get_user()`` macro does this job.
+
+However, user-space memory might well be paged out, which means that
+``get_user()`` might well page-fault and thus block while waiting for the
+resulting I/O to complete.  It would be a very bad thing for the compiler to
+reorder a ``get_user()`` invocation into an RCU read-side critical section.
+
+For example, suppose that the source code looked like this:
+
+  ::
+
+       1 rcu_read_lock();
+       2 p = rcu_dereference(gp);
+       3 v = p->value;
+       4 rcu_read_unlock();
+       5 get_user(user_v, user_p);
+       6 do_something_with(v, user_v);
+
+The compiler must not be permitted to transform this source code into
+the following:
+
+  ::
+
+       1 rcu_read_lock();
+       2 p = rcu_dereference(gp);
+       3 get_user(user_v, user_p); // BUG: POSSIBLE PAGE FAULT!!!
+       4 v = p->value;
+       5 rcu_read_unlock();
+       6 do_something_with(v, user_v);
+
+If the compiler did make this transformation in a ``CONFIG_PREEMPT=n`` kernel
+build, and if ``get_user()`` did page fault, the result would be a quiescent
+state in the middle of an RCU read-side critical section.  This misplaced
+quiescent state could result in line 4 being a use-after-free access,
+which could be bad for your kernel's actuarial statistics.  Similar examples
+can be constructed with the call to ``get_user()`` preceding the
+``rcu_read_lock()``.
+
+Unfortunately, ``get_user()`` doesn't have any particular ordering properties,
+and in some architectures the underlying ``asm`` isn't even marked
+``volatile``.  And even if it was marked ``volatile``, the above access to
+``p->value`` is not volatile, so the compiler would not have any reason to keep
+those two accesses in order.
+
+Therefore, the Linux-kernel definitions of ``rcu_read_lock()`` and
+``rcu_read_unlock()`` must act as compiler barriers, at least for outermost
+instances of ``rcu_read_lock()`` and ``rcu_read_unlock()`` within a nested set
+of RCU read-side critical sections.
+
 Energy Efficiency
 ~~~~~~~~~~~~~~~~~
 
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index e1491d262892..379cb7e50a62 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -288,7 +288,6 @@ void rcu_note_context_switch(bool preempt)
 	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 	struct rcu_node *rnp;
 
-	barrier(); /* Avoid RCU read-side critical sections leaking down. */
 	trace_rcu_utilization(TPS("Start context switch"));
 	lockdep_assert_irqs_disabled();
 	WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
@@ -331,7 +330,6 @@ void rcu_note_context_switch(bool preempt)
 	if (rdp->exp_deferred_qs)
 		rcu_report_exp_rdp(rdp);
 	trace_rcu_utilization(TPS("End context switch"));
-	barrier(); /* Avoid RCU read-side critical sections leaking up. */
 }
 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
 
@@ -815,11 +813,6 @@ static void rcu_qs(void)
  * dyntick-idle quiescent state visible to other CPUs, which will in
  * some cases serve for expedited as well as normal grace periods.
  * Either way, register a lightweight quiescent state.
- *
- * The barrier() calls are redundant in the common case when this is
- * called externally, but just in case this is called from within this
- * file.
- *
  */
 void rcu_all_qs(void)
 {
@@ -834,14 +827,12 @@ void rcu_all_qs(void)
 		return;
 	}
 	this_cpu_write(rcu_data.rcu_urgent_qs, false);
-	barrier(); /* Avoid RCU read-side critical sections leaking down. */
 	if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) {
 		local_irq_save(flags);
 		rcu_momentary_dyntick_idle();
 		local_irq_restore(flags);
 	}
 	rcu_qs();
-	barrier(); /* Avoid RCU read-side critical sections leaking up. */
 	preempt_enable();
 }
 EXPORT_SYMBOL_GPL(rcu_all_qs);
@@ -851,7 +842,6 @@ EXPORT_SYMBOL_GPL(rcu_all_qs);
  */
 void rcu_note_context_switch(bool preempt)
 {
-	barrier(); /* Avoid RCU read-side critical sections leaking down. */
 	trace_rcu_utilization(TPS("Start context switch"));
 	rcu_qs();
 	/* Load rcu_urgent_qs before other flags. */
@@ -864,7 +854,6 @@ void rcu_note_context_switch(bool preempt)
 		rcu_tasks_qs(current);
 out:
 	trace_rcu_utilization(TPS("End context switch"));
-	barrier(); /* Avoid RCU read-side critical sections leaking up. */
 }
 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
 
-- 
2.22.0.770.g0f2c4a37fd-goog

Re: [PATCH 0/9] Apply new rest conversion patches to /dev branch

[Joel Fernandes]

On Thu, Aug 1, 2019 at 2:14 PM Joel Fernandes (Google)
<joel@joelfernandes.org> wrote:
>
> This series fixes the rcu/dev branch so it can apply the new ReST conversion patches.

Weirdly enough, Patch 4/9 did not get received by the archive, but
patchwork did pick it up:
https://lore.kernel.org/patchwork/patch/1109574/

Re: [PATCH 0/9] Apply new rest conversion patches to /dev branch

[Paul E. McKenney]

On Thu, Aug 01, 2019 at 02:14:02PM -0400, Joel Fernandes (Google) wrote:
> This series fixes the rcu/dev branch so it can apply the new ReST conversion patches.
> 
> Patches based on "00ec8f46465e  rcu/nohz: Make multi_cpu_stop() enable tick on
> all online CPUs"
> 
> The easiest was to do this is to revert the patches that conflict and then
> applying the doc patches, and then applying them again. But in the
> re-application, we convert the documentation
> 
> No manual fix ups were done in this process, other than to documentation.

Ah, I was expecting that you would forward-port the conversion, but
yes, that could be painful and error prone.

But given that there are some dependencies on these patches, could you
please use the following alternative procedure for the patches that
touch both code and documentation?

o	Revert only the documentation portion of each commit.  I will
	then merge the partial reverts with the original commits.

o	Apply the documentation conversion.

o	Reapply the documentation portions on top of the conversion.

							Thanx, Paul

> thanks,
> 
>  - Joel
> 
> And in the process I learnt about get_user() and compiler barriers ;-)
> 
> Joel Fernandes (Google) (8):
> Revert "rcu: Restore barrier() to rcu_read_lock() and
> rcu_read_unlock()"
> Revert "rcu: Add support for consolidated-RCU reader checking"
> Revert "treewide: Rename rcu_dereference_raw_notrace() to _check()"
> docs: rcu: Correct links referring to titles
> docs: rcu: Increase toctree to 3
> Revert "Revert "treewide: Rename rcu_dereference_raw_notrace() to
> _check()""
> Revert "Revert "rcu: Add support for consolidated-RCU reader
> checking""
> Revert "Revert "rcu: Restore barrier() to rcu_read_lock() and
> rcu_read_unlock()""
> 
> Mauro Carvalho Chehab (1):
> docs: rcu: convert some articles from html to ReST
> 
> .../Data-Structures/Data-Structures.html      | 1391 -------
> .../Data-Structures/Data-Structures.rst       | 1163 ++++++
> .../Expedited-Grace-Periods.html              |  668 ----
> .../Expedited-Grace-Periods.rst               |  521 +++
> .../Memory-Ordering/Tree-RCU-Diagram.html     |    9 -
> .../Tree-RCU-Memory-Ordering.html             |  704 ----
> .../Tree-RCU-Memory-Ordering.rst              |  624 +++
> .../RCU/Design/Requirements/Requirements.html | 3401 -----------------
> .../RCU/Design/Requirements/Requirements.rst  | 2704 +++++++++++++
> Documentation/RCU/index.rst                   |    7 +-
> Documentation/RCU/whatisRCU.txt               |    4 +-
> 11 files changed, 5020 insertions(+), 6176 deletions(-)
> delete mode 100644 Documentation/RCU/Design/Data-Structures/Data-Structures.html
> create mode 100644 Documentation/RCU/Design/Data-Structures/Data-Structures.rst
> delete mode 100644 Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.html
> create mode 100644 Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst
> delete mode 100644 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Diagram.html
> delete mode 100644 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.html
> create mode 100644 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
> delete mode 100644 Documentation/RCU/Design/Requirements/Requirements.html
> create mode 100644 Documentation/RCU/Design/Requirements/Requirements.rst
> 
> --
> 2.22.0.770.g0f2c4a37fd-goog
> 

Re: [PATCH 0/9] Apply new rest conversion patches to /dev branch

[Joel Fernandes]

On Thu, Aug 1, 2019 at 3:58 PM Paul E. McKenney <paulmck@linux.ibm.com> wrote:
>
> On Thu, Aug 01, 2019 at 02:14:02PM -0400, Joel Fernandes (Google) wrote:
> > This series fixes the rcu/dev branch so it can apply the new ReST conversion patches.
> >
> > Patches based on "00ec8f46465e  rcu/nohz: Make multi_cpu_stop() enable tick on
> > all online CPUs"
> >
> > The easiest was to do this is to revert the patches that conflict and then
> > applying the doc patches, and then applying them again. But in the
> > re-application, we convert the documentation
> >
> > No manual fix ups were done in this process, other than to documentation.
>
> Ah, I was expecting that you would forward-port the conversion, but
> yes, that could be painful and error prone.
>
> But given that there are some dependencies on these patches, could you
> please use the following alternative procedure for the patches that
> touch both code and documentation?
>
> o       Revert only the documentation portion of each commit.  I will
>         then merge the partial reverts with the original commits.
>
> o       Apply the documentation conversion.
>
> o       Reapply the documentation portions on top of the conversion.

Sure, this would be better. I will do this in the evening and send it
to you. Thanks,

 - Joel

Re: [PATCH 0/9] Apply new rest conversion patches to /dev branch

[Paul E. McKenney]

On Thu, Aug 01, 2019 at 04:04:15PM -0400, Joel Fernandes wrote:
> On Thu, Aug 1, 2019 at 3:58 PM Paul E. McKenney <paulmck@linux.ibm.com> wrote:
> >
> > On Thu, Aug 01, 2019 at 02:14:02PM -0400, Joel Fernandes (Google) wrote:
> > > This series fixes the rcu/dev branch so it can apply the new ReST conversion patches.
> > >
> > > Patches based on "00ec8f46465e  rcu/nohz: Make multi_cpu_stop() enable tick on
> > > all online CPUs"
> > >
> > > The easiest was to do this is to revert the patches that conflict and then
> > > applying the doc patches, and then applying them again. But in the
> > > re-application, we convert the documentation
> > >
> > > No manual fix ups were done in this process, other than to documentation.
> >
> > Ah, I was expecting that you would forward-port the conversion, but
> > yes, that could be painful and error prone.
> >
> > But given that there are some dependencies on these patches, could you
> > please use the following alternative procedure for the patches that
> > touch both code and documentation?
> >
> > o       Revert only the documentation portion of each commit.  I will
> >         then merge the partial reverts with the original commits.
> >
> > o       Apply the documentation conversion.
> >
> > o       Reapply the documentation portions on top of the conversion.
> 
> Sure, this would be better. I will do this in the evening and send it
> to you. Thanks,

Very good, looking forward to seeing it!

The smoke tests of the rebase onto v5.3-rc2 passed, so on to create
the usual branches.  Yes, this will complicate merging of the partial
reverts, but there will be the need to apply review comments and the
like anyway, so not really a net increase in complexity.  ;-)

							Thanx, Paul