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Subject[GIT PULL] RCU fix
Linus,

Please pull the latest core-urgent-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git core-urgent-for-linus

HEAD: 40b3c43f042c2ba8915aff5c63708207ed7639cb Merge branch 'rcu/urgent' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/urgent

Thanks,

Ingo

------------------>
Paul E. McKenney (1):
Revert "rcu: Move PREEMPT_RCU preemption to switch_to() invocation"

arch/um/drivers/mconsole_kern.c | 1 -
include/linux/rcupdate.h | 1 -
include/linux/rcutiny.h | 6 ++++++
include/linux/sched.h | 10 ----------
kernel/rcutree.c | 1 +
kernel/rcutree.h | 1 +
kernel/rcutree_plugin.h | 14 +++++++++++---
kernel/sched/core.c | 1 -
8 files changed, 19 insertions(+), 16 deletions(-)
diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
index 88e466b..43b39d6 100644
--- a/arch/um/drivers/mconsole_kern.c
+++ b/arch/um/drivers/mconsole_kern.c
@@ -705,7 +705,6 @@ static void stack_proc(void *arg)
struct task_struct *from = current, *to = arg;

to->thread.saved_task = from;
- rcu_switch_from(from);
switch_to(from, to, from);
}

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 26d1a47..9cac722 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -184,7 +184,6 @@ static inline int rcu_preempt_depth(void)
/* Internal to kernel */
extern void rcu_sched_qs(int cpu);
extern void rcu_bh_qs(int cpu);
-extern void rcu_preempt_note_context_switch(void);
extern void rcu_check_callbacks(int cpu, int user);
struct notifier_block;
extern void rcu_idle_enter(void);
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 854dc4c..4e56a9c 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -87,6 +87,10 @@ static inline void kfree_call_rcu(struct rcu_head *head,

#ifdef CONFIG_TINY_RCU

+static inline void rcu_preempt_note_context_switch(void)
+{
+}
+
static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
{
*delta_jiffies = ULONG_MAX;
@@ -95,6 +99,7 @@ static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)

#else /* #ifdef CONFIG_TINY_RCU */

+void rcu_preempt_note_context_switch(void);
int rcu_preempt_needs_cpu(void);

static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
@@ -108,6 +113,7 @@ static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
static inline void rcu_note_context_switch(int cpu)
{
rcu_sched_qs(cpu);
+ rcu_preempt_note_context_switch();
}

/*
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4059c0f..06a4c5f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1871,22 +1871,12 @@ static inline void rcu_copy_process(struct task_struct *p)
INIT_LIST_HEAD(&p->rcu_node_entry);
}

-static inline void rcu_switch_from(struct task_struct *prev)
-{
- if (prev->rcu_read_lock_nesting != 0)
- rcu_preempt_note_context_switch();
-}
-
#else

static inline void rcu_copy_process(struct task_struct *p)
{
}

-static inline void rcu_switch_from(struct task_struct *prev)
-{
-}
-
#endif

#ifdef CONFIG_SMP
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 38ecdda..4b97bba 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -201,6 +201,7 @@ void rcu_note_context_switch(int cpu)
{
trace_rcu_utilization("Start context switch");
rcu_sched_qs(cpu);
+ rcu_preempt_note_context_switch(cpu);
trace_rcu_utilization("End context switch");
}
EXPORT_SYMBOL_GPL(rcu_note_context_switch);
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index ea05649..19b61ac 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -444,6 +444,7 @@ DECLARE_PER_CPU(char, rcu_cpu_has_work);
/* Forward declarations for rcutree_plugin.h */
static void rcu_bootup_announce(void);
long rcu_batches_completed(void);
+static void rcu_preempt_note_context_switch(int cpu);
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
#ifdef CONFIG_HOTPLUG_CPU
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 5271a02..3e48994 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -153,7 +153,7 @@ static void rcu_preempt_qs(int cpu)
*
* Caller must disable preemption.
*/
-void rcu_preempt_note_context_switch(void)
+static void rcu_preempt_note_context_switch(int cpu)
{
struct task_struct *t = current;
unsigned long flags;
@@ -164,7 +164,7 @@ void rcu_preempt_note_context_switch(void)
(t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {

/* Possibly blocking in an RCU read-side critical section. */
- rdp = __this_cpu_ptr(rcu_preempt_state.rda);
+ rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
rnp = rdp->mynode;
raw_spin_lock_irqsave(&rnp->lock, flags);
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
@@ -228,7 +228,7 @@ void rcu_preempt_note_context_switch(void)
* means that we continue to block the current grace period.
*/
local_irq_save(flags);
- rcu_preempt_qs(smp_processor_id());
+ rcu_preempt_qs(cpu);
local_irq_restore(flags);
}

@@ -1002,6 +1002,14 @@ void rcu_force_quiescent_state(void)
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);

/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * CPUs being in quiescent states.
+ */
+static void rcu_preempt_note_context_switch(int cpu)
+{
+}
+
+/*
* Because preemptible RCU does not exist, there are never any preempted
* RCU readers.
*/
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d5594a4..eaead2d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2081,7 +2081,6 @@ context_switch(struct rq *rq, struct task_struct *prev,
#endif

/* Here we just switch the register state and the stack. */
- rcu_switch_from(prev);
switch_to(prev, next, prev);

barrier();

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