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linux/debian/patches/features/all/rt/rcu-merge-rcu-bh-into-rcu-p...

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Subject: rcu: Merge RCU-bh into RCU-preempt
Date: Wed, 5 Oct 2011 11:59:38 -0700
From: Thomas Gleixner <tglx@linutronix.de>
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.4/patches-4.4.1-rt6.tar.xz
The Linux kernel has long RCU-bh read-side critical sections that
intolerably increase scheduling latency under mainline's RCU-bh rules,
which include RCU-bh read-side critical sections being non-preemptible.
This patch therefore arranges for RCU-bh to be implemented in terms of
RCU-preempt for CONFIG_PREEMPT_RT_FULL=y.
This has the downside of defeating the purpose of RCU-bh, namely,
handling the case where the system is subjected to a network-based
denial-of-service attack that keeps at least one CPU doing full-time
softirq processing. This issue will be fixed by a later commit.
The current commit will need some work to make it appropriate for
mainline use, for example, it needs to be extended to cover Tiny RCU.
[ paulmck: Added a useful changelog ]
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20111005185938.GA20403@linux.vnet.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/rcupdate.h | 23 +++++++++++++++++++++++
include/linux/rcutree.h | 18 ++++++++++++++++--
kernel/rcu/tree.c | 16 ++++++++++++++++
kernel/rcu/update.c | 2 ++
4 files changed, 57 insertions(+), 2 deletions(-)
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -169,6 +169,9 @@ void call_rcu(struct rcu_head *head,
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+#ifdef CONFIG_PREEMPT_RT_FULL
+#define call_rcu_bh call_rcu
+#else
/**
* call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
* @head: structure to be used for queueing the RCU updates.
@@ -192,6 +195,7 @@ void call_rcu(struct rcu_head *head,
*/
void call_rcu_bh(struct rcu_head *head,
rcu_callback_t func);
+#endif
/**
* call_rcu_sched() - Queue an RCU for invocation after sched grace period.
@@ -330,7 +334,11 @@ static inline int rcu_preempt_depth(void
void rcu_init(void);
void rcu_end_inkernel_boot(void);
void rcu_sched_qs(void);
+#ifdef CONFIG_PREEMPT_RT_FULL
+static inline void rcu_bh_qs(void) { }
+#else
void rcu_bh_qs(void);
+#endif
void rcu_check_callbacks(int user);
struct notifier_block;
int rcu_cpu_notify(struct notifier_block *self,
@@ -496,7 +504,14 @@ extern struct lockdep_map rcu_callback_m
int debug_lockdep_rcu_enabled(void);
int rcu_read_lock_held(void);
+#ifdef CONFIG_PREEMPT_RT_FULL
+static inline int rcu_read_lock_bh_held(void)
+{
+ return rcu_read_lock_held();
+}
+#else
int rcu_read_lock_bh_held(void);
+#endif
/**
* rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
@@ -944,10 +959,14 @@ static inline void rcu_read_unlock(void)
static inline void rcu_read_lock_bh(void)
{
local_bh_disable();
+#ifdef CONFIG_PREEMPT_RT_FULL
+ rcu_read_lock();
+#else
__acquire(RCU_BH);
rcu_lock_acquire(&rcu_bh_lock_map);
RCU_LOCKDEP_WARN(!rcu_is_watching(),
"rcu_read_lock_bh() used illegally while idle");
+#endif
}
/*
@@ -957,10 +976,14 @@ static inline void rcu_read_lock_bh(void
*/
static inline void rcu_read_unlock_bh(void)
{
+#ifdef CONFIG_PREEMPT_RT_FULL
+ rcu_read_unlock();
+#else
RCU_LOCKDEP_WARN(!rcu_is_watching(),
"rcu_read_unlock_bh() used illegally while idle");
rcu_lock_release(&rcu_bh_lock_map);
__release(RCU_BH);
+#endif
local_bh_enable();
}
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -44,7 +44,11 @@ static inline void rcu_virt_note_context
rcu_note_context_switch();
}
+#ifdef CONFIG_PREEMPT_RT_FULL
+# define synchronize_rcu_bh synchronize_rcu
+#else
void synchronize_rcu_bh(void);
+#endif
void synchronize_sched_expedited(void);
void synchronize_rcu_expedited(void);
@@ -72,7 +76,11 @@ static inline void synchronize_rcu_bh_ex
}
void rcu_barrier(void);
+#ifdef CONFIG_PREEMPT_RT_FULL
+# define rcu_barrier_bh rcu_barrier
+#else
void rcu_barrier_bh(void);
+#endif
void rcu_barrier_sched(void);
unsigned long get_state_synchronize_rcu(void);
void cond_synchronize_rcu(unsigned long oldstate);
@@ -85,12 +93,10 @@ unsigned long rcu_batches_started(void);
unsigned long rcu_batches_started_bh(void);
unsigned long rcu_batches_started_sched(void);
unsigned long rcu_batches_completed(void);
-unsigned long rcu_batches_completed_bh(void);
unsigned long rcu_batches_completed_sched(void);
void show_rcu_gp_kthreads(void);
void rcu_force_quiescent_state(void);
-void rcu_bh_force_quiescent_state(void);
void rcu_sched_force_quiescent_state(void);
void rcu_idle_enter(void);
@@ -105,6 +111,14 @@ extern int rcu_scheduler_active __read_m
bool rcu_is_watching(void);
+#ifndef CONFIG_PREEMPT_RT_FULL
+void rcu_bh_force_quiescent_state(void);
+unsigned long rcu_batches_completed_bh(void);
+#else
+# define rcu_bh_force_quiescent_state rcu_force_quiescent_state
+# define rcu_batches_completed_bh rcu_batches_completed
+#endif
+
void rcu_all_qs(void);
#endif /* __LINUX_RCUTREE_H */
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -266,6 +266,7 @@ void rcu_sched_qs(void)
}
}
+#ifndef CONFIG_PREEMPT_RT_FULL
void rcu_bh_qs(void)
{
if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) {
@@ -275,6 +276,7 @@ void rcu_bh_qs(void)
__this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false);
}
}
+#endif
static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
@@ -459,6 +461,7 @@ unsigned long rcu_batches_completed_sche
}
EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
+#ifndef CONFIG_PREEMPT_RT_FULL
/*
* Return the number of RCU BH batches completed thus far for debug & stats.
*/
@@ -486,6 +489,13 @@ void rcu_bh_force_quiescent_state(void)
}
EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
+#else
+void rcu_force_quiescent_state(void)
+{
+}
+EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
+#endif
+
/*
* Force a quiescent state for RCU-sched.
*/
@@ -3114,6 +3124,7 @@ void call_rcu_sched(struct rcu_head *hea
}
EXPORT_SYMBOL_GPL(call_rcu_sched);
+#ifndef CONFIG_PREEMPT_RT_FULL
/*
* Queue an RCU callback for invocation after a quicker grace period.
*/
@@ -3122,6 +3133,7 @@ void call_rcu_bh(struct rcu_head *head,
__call_rcu(head, func, &rcu_bh_state, -1, 0);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);
+#endif
/*
* Queue an RCU callback for lazy invocation after a grace period.
@@ -3213,6 +3225,7 @@ void synchronize_sched(void)
}
EXPORT_SYMBOL_GPL(synchronize_sched);
+#ifndef CONFIG_PREEMPT_RT_FULL
/**
* synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
*
@@ -3239,6 +3252,7 @@ void synchronize_rcu_bh(void)
wait_rcu_gp(call_rcu_bh);
}
EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
+#endif
/**
* get_state_synchronize_rcu - Snapshot current RCU state
@@ -4101,6 +4115,7 @@ static void _rcu_barrier(struct rcu_stat
mutex_unlock(&rsp->barrier_mutex);
}
+#ifndef CONFIG_PREEMPT_RT_FULL
/**
* rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
*/
@@ -4109,6 +4124,7 @@ void rcu_barrier_bh(void)
_rcu_barrier(&rcu_bh_state);
}
EXPORT_SYMBOL_GPL(rcu_barrier_bh);
+#endif
/**
* rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -276,6 +276,7 @@ int rcu_read_lock_held(void)
}
EXPORT_SYMBOL_GPL(rcu_read_lock_held);
+#ifndef CONFIG_PREEMPT_RT_FULL
/**
* rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
*
@@ -302,6 +303,7 @@ int rcu_read_lock_bh_held(void)
return in_softirq() || irqs_disabled();
}
EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
+#endif
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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