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[PATCH tip/core/rcu 0/13] Miscellaneous fixes for 4.6

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  [PATCH tip/core/rcu 0/13] Miscellaneous fixes for 4.6 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
    [PATCH tip/core/rcu 01/13] rcu: Assign false instead of 0 for ->core_needs_qs "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
    [PATCH tip/core/rcu 12/13] rcu: Catch up rcu_report_qs_rdp() comment with reality "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
    [PATCH tip/core/rcu 09/13] irq: Privatize irq_common_data::state_use_accessors "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
    [PATCH tip/core/rcu 10/13] rcu: Make rcu/tiny_plugin.h explicitly non-modular "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
    [PATCH tip/core/rcu 04/13] rcu: Set rdp->gpwrap when CPU is idle "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
    [PATCH tip/core/rcu 02/13] rcu: Update rcu_report_qs_rsp() comment "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
    [PATCH tip/core/rcu 07/13] sparse: Add __private to privatize members of structs "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100

#1341551 — [PATCH tip/core/rcu 0/13] Miscellaneous fixes for 4.6

Hello!

This series contains miscellaneous fixes for 4.6:

1.	rcu: Assign false instead of 0 for ->core_needs_qs

2.	Update rcu_report_qs_rsp() comment for RCU's grace-period kthreads.

3.	Stop treating in-kernel CPU-bound workloads as errors, and stop
	IPIing such CPUs unless it is necessary.  (If the loop contains
	cond_resched_rcu_qs(), then it is not necessary!)

4.	Set rdp->gpwrap when CPU is idle instead of doing it backwards.

5.	Correct no-expedite console messages.

6.	Remove useless rcu_data_p when !PREEMPT_RCU, courtesy of Chen Gang.

7-9.	Allow fields to be marked private to allow sparse to complain
	about unauthorized access for rcu_node:: lock and
	irq_common_data::state_use_accessors, courtesy of Boqun Feng.

10.	Make rcu/tiny_plugin.h explicitly non-modular, courtesy of
	Paul Gortmaker.

11.	Document unique-name limitation for DEFINE_STATIC_SRCU(),
	which results from the same per-CPU variable limitation.

12.	Catch up rcu_report_qs_rdp() comment with reality.

13.	Remove rcu_user_hooks_switch, courtesy of Yang Shi.

							Thanx, Paul

------------------------------------------------------------------------

 include/linux/compiler.h |   12 ++-
 include/linux/irq.h      |    6 +
 include/linux/rcupdate.h |    2 
 include/linux/srcu.h     |   19 +++++-
 kernel/irq/internals.h   |    4 +
 kernel/rcu/rcutorture.c  |   14 ++--
 kernel/rcu/tiny_plugin.h |   15 ----
 kernel/rcu/tree.c        |  143 +++++++++++++++++++++++------------------------
 kernel/rcu/tree.h        |   42 ++++++++++---
 kernel/rcu/tree_plugin.h |   27 ++++----
 scripts/checkpatch.pl    |    3 
 11 files changed, 159 insertions(+), 128 deletions(-)

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#1341553 — [PATCH tip/core/rcu 01/13] rcu: Assign false instead of 0 for ->core_needs_qs

A zero seems to have escaped earlier true/false substitution efforts,
so this commit changes 0 to false for the ->core_needs_qs boolean field.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index e41dd4131f7a..b8bbf3b27241 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2390,7 +2390,7 @@ rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
 	if ((rnp->qsmask & mask) == 0) {
 		raw_spin_unlock_irqrestore(&rnp->lock, flags);
 	} else {
-		rdp->core_needs_qs = 0;
+		rdp->core_needs_qs = false;
 
 		/*
 		 * This GP can't end until cpu checks in, so all of our
-- 
2.5.2

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#1341556 — [PATCH tip/core/rcu 12/13] rcu: Catch up rcu_report_qs_rdp() comment with reality

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index d5a6d2f0cbf4..39f9c73d33c5 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2354,12 +2354,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
 
 /*
  * Record a quiescent state for the specified CPU to that CPU's rcu_data
- * structure.  This must be either called from the specified CPU, or
- * called when the specified CPU is known to be offline (and when it is
- * also known that no other CPU is concurrently trying to help the offline
- * CPU).  The lastcomp argument is used to make sure we are still in the
- * grace period of interest.  We don't want to end the current grace period
- * based on quiescent states detected in an earlier grace period!
+ * structure.  This must be called from the specified CPU.
  */
 static void
 rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
-- 
2.5.2

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#1341558 — [PATCH tip/core/rcu 09/13] irq: Privatize irq_common_data::state_use_accessors

From: Boqun Feng <boqun.feng@gmail.com>

irq_common_data::state_use_accessors is not designed for public use.
Therefore make it private so that people who write code accessing it
directly will get blamed by sparse. Also #undef the macro
__irqd_to_state after used in header files, so that the macro can't be
misused.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/irq.h    | 6 ++++--
 kernel/irq/internals.h | 4 ++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/linux/irq.h b/include/linux/irq.h
index 3c1c96786248..cd14cd4a22b4 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -137,7 +137,7 @@ struct irq_domain;
  * @msi_desc:		MSI descriptor
  */
 struct irq_common_data {
-	unsigned int		state_use_accessors;
+	unsigned int		__private state_use_accessors;
 #ifdef CONFIG_NUMA
 	unsigned int		node;
 #endif
@@ -208,7 +208,7 @@ enum {
 	IRQD_FORWARDED_TO_VCPU		= (1 << 20),
 };
 
-#define __irqd_to_state(d)		((d)->common->state_use_accessors)
+#define __irqd_to_state(d) ACCESS_PRIVATE((d)->common, state_use_accessors)
 
 static inline bool irqd_is_setaffinity_pending(struct irq_data *d)
 {
@@ -299,6 +299,8 @@ static inline void irqd_clr_forwarded_to_vcpu(struct irq_data *d)
 	__irqd_to_state(d) &= ~IRQD_FORWARDED_TO_VCPU;
 }
 
+#undef __irqd_to_state
+
 static inline irq_hw_number_t irqd_to_hwirq(struct irq_data *d)
 {
 	return d->hwirq;
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index fcab63c66905..3d182932d2d1 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -160,6 +160,8 @@ irq_put_desc_unlock(struct irq_desc *desc, unsigned long flags)
 	__irq_put_desc_unlock(desc, flags, false);
 }
 
+#define __irqd_to_state(d) ACCESS_PRIVATE((d)->common, state_use_accessors)
+
 /*
  * Manipulation functions for irq_data.state
  */
@@ -188,6 +190,8 @@ static inline bool irqd_has_set(struct irq_data *d, unsigned int mask)
 	return __irqd_to_state(d) & mask;
 }
 
+#undef __irqd_to_state
+
 static inline void kstat_incr_irqs_this_cpu(struct irq_desc *desc)
 {
 	__this_cpu_inc(*desc->kstat_irqs);
-- 
2.5.2

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#1341559 — [PATCH tip/core/rcu 10/13] rcu: Make rcu/tiny_plugin.h explicitly non-modular

From: Paul Gortmaker <paul.gortmaker@windriver.com>

The Kconfig currently controlling compilation of this code is:

init/Kconfig:config TINY_RCU
init/Kconfig:   bool

...meaning that it currently is not being built as a module by anyone.

Lets remove the modular code that is essentially orphaned, so that
when reading the code there is no doubt it is builtin-only.

Since module_init translates to device_initcall in the non-modular
case, the init ordering remains unchanged with this commit.  We could
consider moving this to an earlier initcall (subsys?) if desired.

We also delete the MODULE_LICENSE tag etc. since all that information
is already contained at the top of the file in the comments.

Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tiny_plugin.h | 15 ++-------------
 1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/kernel/rcu/tiny_plugin.h b/kernel/rcu/tiny_plugin.h
index e492a5253e0f..196f0302e2f4 100644
--- a/kernel/rcu/tiny_plugin.h
+++ b/kernel/rcu/tiny_plugin.h
@@ -23,7 +23,7 @@
  */
 
 #include <linux/kthread.h>
-#include <linux/module.h>
+#include <linux/init.h>
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
 
@@ -122,18 +122,7 @@ free_out:
 	debugfs_remove_recursive(rcudir);
 	return 1;
 }
-
-static void __exit rcutiny_trace_cleanup(void)
-{
-	debugfs_remove_recursive(rcudir);
-}
-
-module_init(rcutiny_trace_init);
-module_exit(rcutiny_trace_cleanup);
-
-MODULE_AUTHOR("Paul E. McKenney");
-MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
-MODULE_LICENSE("GPL");
+device_initcall(rcutiny_trace_init);
 
 static void check_cpu_stall(struct rcu_ctrlblk *rcp)
 {
-- 
2.5.2

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#1341561 — [PATCH tip/core/rcu 04/13] rcu: Set rdp->gpwrap when CPU is idle

Commit #e3663b1024d1 ("rcu: Handle gpnum/completed wrap while dyntick
idle") sets rdp->gpwrap on the wrong side of the "if" statement in
dyntick_save_progress_counter(), that is, it sets it when the CPU is
not idle instead of when it is idle.  Of course, if the CPU is not idle,
its rdp->gpnum won't be lagging beind the global rsp->gpnum, which means
that rdp->gpwrap will never be set.

This commit therefore moves this code to the proper leg of that "if"
statement.  This change means that the "else" cause is just "return 0"
and the "then" clause ends with "return 1", so also move the "return 0"
to follow the "if", dropping the "else" clause.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 68f4bee3ecc3..976a166f3fa3 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1083,13 +1083,12 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp,
 	rcu_sysidle_check_cpu(rdp, isidle, maxj);
 	if ((rdp->dynticks_snap & 0x1) == 0) {
 		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
-		return 1;
-	} else {
 		if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4,
 				 rdp->mynode->gpnum))
 			WRITE_ONCE(rdp->gpwrap, true);
-		return 0;
+		return 1;
 	}
+	return 0;
 }
 
 /*
-- 
2.5.2

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#1341563 — [PATCH tip/core/rcu 02/13] rcu: Update rcu_report_qs_rsp() comment

The header comment for rcu_report_qs_rsp() was obsolete, dating well
before the advent of RCU grace-period kthreads.  This commit therefore
brings this comment back into alignment with current reality.

Reported-by: Lihao Liang <lihao.liang@cs.ox.ac.uk>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b8bbf3b27241..a91836868ade 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2234,11 +2234,13 @@ static bool rcu_start_gp(struct rcu_state *rsp)
 }
 
 /*
- * Report a full set of quiescent states to the specified rcu_state
- * data structure.  This involves cleaning up after the prior grace
- * period and letting rcu_start_gp() start up the next grace period
- * if one is needed.  Note that the caller must hold rnp->lock, which
- * is released before return.
+ * Report a full set of quiescent states to the specified rcu_state data
+ * structure.  Invoke rcu_gp_kthread_wake() to awaken the grace-period
+ * kthread if another grace period is required.  Whether we wake
+ * the grace-period kthread or it awakens itself for the next round
+ * of quiescent-state forcing, that kthread will clean up after the
+ * just-completed grace period.  Note that the caller must hold rnp->lock,
+ * which is released before return.
  */
 static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
 	__releases(rcu_get_root(rsp)->lock)
-- 
2.5.2

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#1341565 — [PATCH tip/core/rcu 07/13] sparse: Add __private to privatize members of structs

From: Boqun Feng <boqun.feng@gmail.com>

In C programming language, we don't have a easy way to privatize a
member of a structure. However in kernel, sometimes there is a need to
privatize a member in case of potential bugs or misuses.

Fortunately, the noderef attribute of sparse is a way to privatize a
member, as by defining a member as noderef, the address-of operator on
the member will produce a noderef pointer to that member, and if anyone
wants to dereference that kind of pointers to read or modify the member,
sparse will yell.

Based on this, __private modifier and related operation ACCESS_PRIVATE()
are introduced, which could help detect undesigned public uses of
private members of structs. Here is an example of sparse's output if it
detect an undersigned public use:

| kernel/rcu/tree.c:4453:25: warning: incorrect type in argument 1 (different modifiers)
| kernel/rcu/tree.c:4453:25:    expected struct raw_spinlock [usertype] *lock
| kernel/rcu/tree.c:4453:25:    got struct raw_spinlock [noderef] *<noident>

Also, this patch improves compiler.h a little bit by adding comments for
"#else" and "#endif".

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/compiler.h | 12 ++++++++----
 scripts/checkpatch.pl    |  3 ++-
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 00b042c49ccd..c845356952bb 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -20,12 +20,14 @@
 # define __pmem		__attribute__((noderef, address_space(5)))
 #ifdef CONFIG_SPARSE_RCU_POINTER
 # define __rcu		__attribute__((noderef, address_space(4)))
-#else
+#else /* CONFIG_SPARSE_RCU_POINTER */
 # define __rcu
-#endif
+#endif /* CONFIG_SPARSE_RCU_POINTER */
+# define __private	__attribute__((noderef))
 extern void __chk_user_ptr(const volatile void __user *);
 extern void __chk_io_ptr(const volatile void __iomem *);
-#else
+# define ACCESS_PRIVATE(p, member) (*((typeof((p)->member) __force *) &(p)->member))
+#else /* __CHECKER__ */
 # define __user
 # define __kernel
 # define __safe
@@ -44,7 +46,9 @@ extern void __chk_io_ptr(const volatile void __iomem *);
 # define __percpu
 # define __rcu
 # define __pmem
-#endif
+# define __private
+# define ACCESS_PRIVATE(p, member) ((p)->member)
+#endif /* __CHECKER__ */
 
 /* Indirect macros required for expanded argument pasting, eg. __LINE__. */
 #define ___PASTE(a,b) a##b
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 0147c91fa549..874132b26d23 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -269,7 +269,8 @@ our $Sparse	= qr{
 			__init_refok|
 			__kprobes|
 			__ref|
-			__rcu
+			__rcu|
+			__private
 		}x;
 our $InitAttributePrefix = qr{__(?:mem|cpu|dev|net_|)};
 our $InitAttributeData = qr{$InitAttributePrefix(?:initdata\b)};
-- 
2.5.2

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