File-copy from v4.4.100
This is the result of 'cp' from a linux-stable tree with the 'v4.4.100'
tag checked out (commit 26d6298789e695c9f627ce49a7bbd2286405798a) on
git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
Please refer to that tree for all history prior to this point.
Change-Id: I8a9ee2aea93cd29c52c847d0ce33091a73ae6afe
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
new file mode 100644
index 0000000..a0189ba
--- /dev/null
+++ b/include/linux/rcupdate.h
@@ -0,0 +1,1138 @@
+/*
+ * Read-Copy Update mechanism for mutual exclusion
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright IBM Corporation, 2001
+ *
+ * Author: Dipankar Sarma <dipankar@in.ibm.com>
+ *
+ * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
+ * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
+ * Papers:
+ * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
+ * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * http://lse.sourceforge.net/locking/rcupdate.html
+ *
+ */
+
+#ifndef __LINUX_RCUPDATE_H
+#define __LINUX_RCUPDATE_H
+
+#include <linux/types.h>
+#include <linux/cache.h>
+#include <linux/spinlock.h>
+#include <linux/threads.h>
+#include <linux/cpumask.h>
+#include <linux/seqlock.h>
+#include <linux/lockdep.h>
+#include <linux/completion.h>
+#include <linux/debugobjects.h>
+#include <linux/bug.h>
+#include <linux/compiler.h>
+#include <linux/ktime.h>
+
+#include <asm/barrier.h>
+
+extern int rcu_expedited; /* for sysctl */
+
+#ifdef CONFIG_TINY_RCU
+/* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
+static inline bool rcu_gp_is_expedited(void) /* Internal RCU use. */
+{
+ return false;
+}
+
+static inline void rcu_expedite_gp(void)
+{
+}
+
+static inline void rcu_unexpedite_gp(void)
+{
+}
+#else /* #ifdef CONFIG_TINY_RCU */
+bool rcu_gp_is_expedited(void); /* Internal RCU use. */
+void rcu_expedite_gp(void);
+void rcu_unexpedite_gp(void);
+#endif /* #else #ifdef CONFIG_TINY_RCU */
+
+enum rcutorture_type {
+ RCU_FLAVOR,
+ RCU_BH_FLAVOR,
+ RCU_SCHED_FLAVOR,
+ RCU_TASKS_FLAVOR,
+ SRCU_FLAVOR,
+ INVALID_RCU_FLAVOR
+};
+
+#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
+void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
+ unsigned long *gpnum, unsigned long *completed);
+void rcutorture_record_test_transition(void);
+void rcutorture_record_progress(unsigned long vernum);
+void do_trace_rcu_torture_read(const char *rcutorturename,
+ struct rcu_head *rhp,
+ unsigned long secs,
+ unsigned long c_old,
+ unsigned long c);
+#else
+static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
+ int *flags,
+ unsigned long *gpnum,
+ unsigned long *completed)
+{
+ *flags = 0;
+ *gpnum = 0;
+ *completed = 0;
+}
+static inline void rcutorture_record_test_transition(void)
+{
+}
+static inline void rcutorture_record_progress(unsigned long vernum)
+{
+}
+#ifdef CONFIG_RCU_TRACE
+void do_trace_rcu_torture_read(const char *rcutorturename,
+ struct rcu_head *rhp,
+ unsigned long secs,
+ unsigned long c_old,
+ unsigned long c);
+#else
+#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
+ do { } while (0)
+#endif
+#endif
+
+#define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b))
+#define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b))
+#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
+#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
+#define ulong2long(a) (*(long *)(&(a)))
+
+/* Exported common interfaces */
+
+#ifdef CONFIG_PREEMPT_RCU
+
+/**
+ * call_rcu() - Queue an RCU callback for invocation after a grace period.
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all pre-existing RCU read-side
+ * critical sections have completed. However, the callback function
+ * might well execute concurrently with RCU read-side critical sections
+ * that started after call_rcu() was invoked. RCU read-side critical
+ * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
+ * and may be nested.
+ *
+ * Note that all CPUs must agree that the grace period extended beyond
+ * all pre-existing RCU read-side critical section. On systems with more
+ * than one CPU, this means that when "func()" is invoked, each CPU is
+ * guaranteed to have executed a full memory barrier since the end of its
+ * last RCU read-side critical section whose beginning preceded the call
+ * to call_rcu(). It also means that each CPU executing an RCU read-side
+ * critical section that continues beyond the start of "func()" must have
+ * executed a memory barrier after the call_rcu() but before the beginning
+ * of that RCU read-side critical section. Note that these guarantees
+ * include CPUs that are offline, idle, or executing in user mode, as
+ * well as CPUs that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
+ * resulting RCU callback function "func()", then both CPU A and CPU B are
+ * guaranteed to execute a full memory barrier during the time interval
+ * between the call to call_rcu() and the invocation of "func()" -- even
+ * if CPU A and CPU B are the same CPU (but again only if the system has
+ * more than one CPU).
+ */
+void call_rcu(struct rcu_head *head,
+ rcu_callback_t func);
+
+#else /* #ifdef CONFIG_PREEMPT_RCU */
+
+/* In classic RCU, call_rcu() is just call_rcu_sched(). */
+#define call_rcu call_rcu_sched
+
+#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+
+/**
+ * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. call_rcu_bh() assumes
+ * that the read-side critical sections end on completion of a softirq
+ * handler. This means that read-side critical sections in process
+ * context must not be interrupted by softirqs. This interface is to be
+ * used when most of the read-side critical sections are in softirq context.
+ * RCU read-side critical sections are delimited by :
+ * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
+ * OR
+ * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
+ * These may be nested.
+ *
+ * See the description of call_rcu() for more detailed information on
+ * memory ordering guarantees.
+ */
+void call_rcu_bh(struct rcu_head *head,
+ rcu_callback_t func);
+
+/**
+ * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. call_rcu_sched() assumes
+ * that the read-side critical sections end on enabling of preemption
+ * or on voluntary preemption.
+ * RCU read-side critical sections are delimited by :
+ * - rcu_read_lock_sched() and rcu_read_unlock_sched(),
+ * OR
+ * anything that disables preemption.
+ * These may be nested.
+ *
+ * See the description of call_rcu() for more detailed information on
+ * memory ordering guarantees.
+ */
+void call_rcu_sched(struct rcu_head *head,
+ rcu_callback_t func);
+
+void synchronize_sched(void);
+
+/*
+ * Structure allowing asynchronous waiting on RCU.
+ */
+struct rcu_synchronize {
+ struct rcu_head head;
+ struct completion completion;
+};
+void wakeme_after_rcu(struct rcu_head *head);
+
+void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
+ struct rcu_synchronize *rs_array);
+
+#define _wait_rcu_gp(checktiny, ...) \
+do { \
+ call_rcu_func_t __crcu_array[] = { __VA_ARGS__ }; \
+ struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)]; \
+ __wait_rcu_gp(checktiny, ARRAY_SIZE(__crcu_array), \
+ __crcu_array, __rs_array); \
+} while (0)
+
+#define wait_rcu_gp(...) _wait_rcu_gp(false, __VA_ARGS__)
+
+/**
+ * synchronize_rcu_mult - Wait concurrently for multiple grace periods
+ * @...: List of call_rcu() functions for the flavors to wait on.
+ *
+ * This macro waits concurrently for multiple flavors of RCU grace periods.
+ * For example, synchronize_rcu_mult(call_rcu, call_rcu_bh) would wait
+ * on concurrent RCU and RCU-bh grace periods. Waiting on a give SRCU
+ * domain requires you to write a wrapper function for that SRCU domain's
+ * call_srcu() function, supplying the corresponding srcu_struct.
+ *
+ * If Tiny RCU, tell _wait_rcu_gp() not to bother waiting for RCU
+ * or RCU-bh, given that anywhere synchronize_rcu_mult() can be called
+ * is automatically a grace period.
+ */
+#define synchronize_rcu_mult(...) \
+ _wait_rcu_gp(IS_ENABLED(CONFIG_TINY_RCU), __VA_ARGS__)
+
+/**
+ * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. call_rcu_tasks() assumes
+ * that the read-side critical sections end at a voluntary context
+ * switch (not a preemption!), entry into idle, or transition to usermode
+ * execution. As such, there are no read-side primitives analogous to
+ * rcu_read_lock() and rcu_read_unlock() because this primitive is intended
+ * to determine that all tasks have passed through a safe state, not so
+ * much for data-strcuture synchronization.
+ *
+ * See the description of call_rcu() for more detailed information on
+ * memory ordering guarantees.
+ */
+void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
+void synchronize_rcu_tasks(void);
+void rcu_barrier_tasks(void);
+
+#ifdef CONFIG_PREEMPT_RCU
+
+void __rcu_read_lock(void);
+void __rcu_read_unlock(void);
+void rcu_read_unlock_special(struct task_struct *t);
+void synchronize_rcu(void);
+
+/*
+ * Defined as a macro as it is a very low level header included from
+ * areas that don't even know about current. This gives the rcu_read_lock()
+ * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
+ * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
+ */
+#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
+
+#else /* #ifdef CONFIG_PREEMPT_RCU */
+
+static inline void __rcu_read_lock(void)
+{
+ if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
+ preempt_disable();
+}
+
+static inline void __rcu_read_unlock(void)
+{
+ if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
+ preempt_enable();
+}
+
+static inline void synchronize_rcu(void)
+{
+ synchronize_sched();
+}
+
+static inline int rcu_preempt_depth(void)
+{
+ return 0;
+}
+
+#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+
+/* Internal to kernel */
+void rcu_init(void);
+void rcu_end_inkernel_boot(void);
+void rcu_sched_qs(void);
+void rcu_bh_qs(void);
+void rcu_check_callbacks(int user);
+struct notifier_block;
+int rcu_cpu_notify(struct notifier_block *self,
+ unsigned long action, void *hcpu);
+
+#ifdef CONFIG_RCU_STALL_COMMON
+void rcu_sysrq_start(void);
+void rcu_sysrq_end(void);
+#else /* #ifdef CONFIG_RCU_STALL_COMMON */
+static inline void rcu_sysrq_start(void)
+{
+}
+static inline void rcu_sysrq_end(void)
+{
+}
+#endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
+
+#ifdef CONFIG_NO_HZ_FULL
+void rcu_user_enter(void);
+void rcu_user_exit(void);
+#else
+static inline void rcu_user_enter(void) { }
+static inline void rcu_user_exit(void) { }
+static inline void rcu_user_hooks_switch(struct task_struct *prev,
+ struct task_struct *next) { }
+#endif /* CONFIG_NO_HZ_FULL */
+
+#ifdef CONFIG_RCU_NOCB_CPU
+void rcu_init_nohz(void);
+#else /* #ifdef CONFIG_RCU_NOCB_CPU */
+static inline void rcu_init_nohz(void)
+{
+}
+#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
+
+/**
+ * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
+ * @a: Code that RCU needs to pay attention to.
+ *
+ * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
+ * in the inner idle loop, that is, between the rcu_idle_enter() and
+ * the rcu_idle_exit() -- RCU will happily ignore any such read-side
+ * critical sections. However, things like powertop need tracepoints
+ * in the inner idle loop.
+ *
+ * This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
+ * will tell RCU that it needs to pay attending, invoke its argument
+ * (in this example, a call to the do_something_with_RCU() function),
+ * and then tell RCU to go back to ignoring this CPU. It is permissible
+ * to nest RCU_NONIDLE() wrappers, but the nesting level is currently
+ * quite limited. If deeper nesting is required, it will be necessary
+ * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
+ */
+#define RCU_NONIDLE(a) \
+ do { \
+ rcu_irq_enter(); \
+ do { a; } while (0); \
+ rcu_irq_exit(); \
+ } while (0)
+
+/*
+ * Note a voluntary context switch for RCU-tasks benefit. This is a
+ * macro rather than an inline function to avoid #include hell.
+ */
+#ifdef CONFIG_TASKS_RCU
+#define TASKS_RCU(x) x
+extern struct srcu_struct tasks_rcu_exit_srcu;
+#define rcu_note_voluntary_context_switch(t) \
+ do { \
+ rcu_all_qs(); \
+ if (READ_ONCE((t)->rcu_tasks_holdout)) \
+ WRITE_ONCE((t)->rcu_tasks_holdout, false); \
+ } while (0)
+#else /* #ifdef CONFIG_TASKS_RCU */
+#define TASKS_RCU(x) do { } while (0)
+#define rcu_note_voluntary_context_switch(t) rcu_all_qs()
+#endif /* #else #ifdef CONFIG_TASKS_RCU */
+
+/**
+ * cond_resched_rcu_qs - Report potential quiescent states to RCU
+ *
+ * This macro resembles cond_resched(), except that it is defined to
+ * report potential quiescent states to RCU-tasks even if the cond_resched()
+ * machinery were to be shut off, as some advocate for PREEMPT kernels.
+ */
+#define cond_resched_rcu_qs() \
+do { \
+ if (!cond_resched()) \
+ rcu_note_voluntary_context_switch(current); \
+} while (0)
+
+#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
+bool __rcu_is_watching(void);
+#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
+
+/*
+ * Infrastructure to implement the synchronize_() primitives in
+ * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
+ */
+
+#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
+#include <linux/rcutree.h>
+#elif defined(CONFIG_TINY_RCU)
+#include <linux/rcutiny.h>
+#else
+#error "Unknown RCU implementation specified to kernel configuration"
+#endif
+
+/*
+ * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
+ * initialization and destruction of rcu_head on the stack. rcu_head structures
+ * allocated dynamically in the heap or defined statically don't need any
+ * initialization.
+ */
+#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
+void init_rcu_head(struct rcu_head *head);
+void destroy_rcu_head(struct rcu_head *head);
+void init_rcu_head_on_stack(struct rcu_head *head);
+void destroy_rcu_head_on_stack(struct rcu_head *head);
+#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
+static inline void init_rcu_head(struct rcu_head *head)
+{
+}
+
+static inline void destroy_rcu_head(struct rcu_head *head)
+{
+}
+
+static inline void init_rcu_head_on_stack(struct rcu_head *head)
+{
+}
+
+static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
+{
+}
+#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
+
+#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
+bool rcu_lockdep_current_cpu_online(void);
+#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
+static inline bool rcu_lockdep_current_cpu_online(void)
+{
+ return true;
+}
+#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
+static inline void rcu_lock_acquire(struct lockdep_map *map)
+{
+ lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
+}
+
+static inline void rcu_lock_release(struct lockdep_map *map)
+{
+ lock_release(map, 1, _THIS_IP_);
+}
+
+extern struct lockdep_map rcu_lock_map;
+extern struct lockdep_map rcu_bh_lock_map;
+extern struct lockdep_map rcu_sched_lock_map;
+extern struct lockdep_map rcu_callback_map;
+int debug_lockdep_rcu_enabled(void);
+
+int rcu_read_lock_held(void);
+int rcu_read_lock_bh_held(void);
+
+/**
+ * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
+ *
+ * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
+ * RCU-sched read-side critical section. In absence of
+ * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
+ * critical section unless it can prove otherwise.
+ */
+#ifdef CONFIG_PREEMPT_COUNT
+int rcu_read_lock_sched_held(void);
+#else /* #ifdef CONFIG_PREEMPT_COUNT */
+static inline int rcu_read_lock_sched_held(void)
+{
+ return 1;
+}
+#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
+
+#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+# define rcu_lock_acquire(a) do { } while (0)
+# define rcu_lock_release(a) do { } while (0)
+
+static inline int rcu_read_lock_held(void)
+{
+ return 1;
+}
+
+static inline int rcu_read_lock_bh_held(void)
+{
+ return 1;
+}
+
+#ifdef CONFIG_PREEMPT_COUNT
+static inline int rcu_read_lock_sched_held(void)
+{
+ return preempt_count() != 0 || irqs_disabled();
+}
+#else /* #ifdef CONFIG_PREEMPT_COUNT */
+static inline int rcu_read_lock_sched_held(void)
+{
+ return 1;
+}
+#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
+
+#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+#ifdef CONFIG_PROVE_RCU
+
+/**
+ * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
+ * @c: condition to check
+ * @s: informative message
+ */
+#define RCU_LOCKDEP_WARN(c, s) \
+ do { \
+ static bool __section(.data.unlikely) __warned; \
+ if (debug_lockdep_rcu_enabled() && !__warned && (c)) { \
+ __warned = true; \
+ lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
+ } \
+ } while (0)
+
+#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
+static inline void rcu_preempt_sleep_check(void)
+{
+ RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
+ "Illegal context switch in RCU read-side critical section");
+}
+#else /* #ifdef CONFIG_PROVE_RCU */
+static inline void rcu_preempt_sleep_check(void)
+{
+}
+#endif /* #else #ifdef CONFIG_PROVE_RCU */
+
+#define rcu_sleep_check() \
+ do { \
+ rcu_preempt_sleep_check(); \
+ RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map), \
+ "Illegal context switch in RCU-bh read-side critical section"); \
+ RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
+ "Illegal context switch in RCU-sched read-side critical section"); \
+ } while (0)
+
+#else /* #ifdef CONFIG_PROVE_RCU */
+
+#define RCU_LOCKDEP_WARN(c, s) do { } while (0)
+#define rcu_sleep_check() do { } while (0)
+
+#endif /* #else #ifdef CONFIG_PROVE_RCU */
+
+/*
+ * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
+ * and rcu_assign_pointer(). Some of these could be folded into their
+ * callers, but they are left separate in order to ease introduction of
+ * multiple flavors of pointers to match the multiple flavors of RCU
+ * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
+ * the future.
+ */
+
+#ifdef __CHECKER__
+#define rcu_dereference_sparse(p, space) \
+ ((void)(((typeof(*p) space *)p) == p))
+#else /* #ifdef __CHECKER__ */
+#define rcu_dereference_sparse(p, space)
+#endif /* #else #ifdef __CHECKER__ */
+
+#define __rcu_access_pointer(p, space) \
+({ \
+ typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
+ rcu_dereference_sparse(p, space); \
+ ((typeof(*p) __force __kernel *)(_________p1)); \
+})
+#define __rcu_dereference_check(p, c, space) \
+({ \
+ /* Dependency order vs. p above. */ \
+ typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
+ RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
+ rcu_dereference_sparse(p, space); \
+ ((typeof(*p) __force __kernel *)(________p1)); \
+})
+#define __rcu_dereference_protected(p, c, space) \
+({ \
+ RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
+ rcu_dereference_sparse(p, space); \
+ ((typeof(*p) __force __kernel *)(p)); \
+})
+
+/**
+ * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
+ * @v: The value to statically initialize with.
+ */
+#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
+
+/**
+ * rcu_assign_pointer() - assign to RCU-protected pointer
+ * @p: pointer to assign to
+ * @v: value to assign (publish)
+ *
+ * Assigns the specified value to the specified RCU-protected
+ * pointer, ensuring that any concurrent RCU readers will see
+ * any prior initialization.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (which is most of them), and also prevents the compiler from
+ * reordering the code that initializes the structure after the pointer
+ * assignment. More importantly, this call documents which pointers
+ * will be dereferenced by RCU read-side code.
+ *
+ * In some special cases, you may use RCU_INIT_POINTER() instead
+ * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
+ * to the fact that it does not constrain either the CPU or the compiler.
+ * That said, using RCU_INIT_POINTER() when you should have used
+ * rcu_assign_pointer() is a very bad thing that results in
+ * impossible-to-diagnose memory corruption. So please be careful.
+ * See the RCU_INIT_POINTER() comment header for details.
+ *
+ * Note that rcu_assign_pointer() evaluates each of its arguments only
+ * once, appearances notwithstanding. One of the "extra" evaluations
+ * is in typeof() and the other visible only to sparse (__CHECKER__),
+ * neither of which actually execute the argument. As with most cpp
+ * macros, this execute-arguments-only-once property is important, so
+ * please be careful when making changes to rcu_assign_pointer() and the
+ * other macros that it invokes.
+ */
+#define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
+
+/**
+ * rcu_access_pointer() - fetch RCU pointer with no dereferencing
+ * @p: The pointer to read
+ *
+ * Return the value of the specified RCU-protected pointer, but omit the
+ * smp_read_barrier_depends() and keep the READ_ONCE(). This is useful
+ * when the value of this pointer is accessed, but the pointer is not
+ * dereferenced, for example, when testing an RCU-protected pointer against
+ * NULL. Although rcu_access_pointer() may also be used in cases where
+ * update-side locks prevent the value of the pointer from changing, you
+ * should instead use rcu_dereference_protected() for this use case.
+ *
+ * It is also permissible to use rcu_access_pointer() when read-side
+ * access to the pointer was removed at least one grace period ago, as
+ * is the case in the context of the RCU callback that is freeing up
+ * the data, or after a synchronize_rcu() returns. This can be useful
+ * when tearing down multi-linked structures after a grace period
+ * has elapsed.
+ */
+#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
+
+/**
+ * rcu_dereference_check() - rcu_dereference with debug checking
+ * @p: The pointer to read, prior to dereferencing
+ * @c: The conditions under which the dereference will take place
+ *
+ * Do an rcu_dereference(), but check that the conditions under which the
+ * dereference will take place are correct. Typically the conditions
+ * indicate the various locking conditions that should be held at that
+ * point. The check should return true if the conditions are satisfied.
+ * An implicit check for being in an RCU read-side critical section
+ * (rcu_read_lock()) is included.
+ *
+ * For example:
+ *
+ * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
+ *
+ * could be used to indicate to lockdep that foo->bar may only be dereferenced
+ * if either rcu_read_lock() is held, or that the lock required to replace
+ * the bar struct at foo->bar is held.
+ *
+ * Note that the list of conditions may also include indications of when a lock
+ * need not be held, for example during initialisation or destruction of the
+ * target struct:
+ *
+ * bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
+ * atomic_read(&foo->usage) == 0);
+ *
+ * Inserts memory barriers on architectures that require them
+ * (currently only the Alpha), prevents the compiler from refetching
+ * (and from merging fetches), and, more importantly, documents exactly
+ * which pointers are protected by RCU and checks that the pointer is
+ * annotated as __rcu.
+ */
+#define rcu_dereference_check(p, c) \
+ __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
+
+/**
+ * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
+ * @p: The pointer to read, prior to dereferencing
+ * @c: The conditions under which the dereference will take place
+ *
+ * This is the RCU-bh counterpart to rcu_dereference_check().
+ */
+#define rcu_dereference_bh_check(p, c) \
+ __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
+
+/**
+ * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
+ * @p: The pointer to read, prior to dereferencing
+ * @c: The conditions under which the dereference will take place
+ *
+ * This is the RCU-sched counterpart to rcu_dereference_check().
+ */
+#define rcu_dereference_sched_check(p, c) \
+ __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
+ __rcu)
+
+#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
+
+/*
+ * The tracing infrastructure traces RCU (we want that), but unfortunately
+ * some of the RCU checks causes tracing to lock up the system.
+ *
+ * The 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)
+
+/**
+ * rcu_dereference_protected() - fetch RCU pointer when updates prevented
+ * @p: The pointer to read, prior to dereferencing
+ * @c: The conditions under which the dereference will take place
+ *
+ * Return the value of the specified RCU-protected pointer, but omit
+ * both the smp_read_barrier_depends() and the READ_ONCE(). This
+ * is useful in cases where update-side locks prevent the value of the
+ * pointer from changing. Please note that this primitive does -not-
+ * prevent the compiler from repeating this reference or combining it
+ * with other references, so it should not be used without protection
+ * of appropriate locks.
+ *
+ * This function is only for update-side use. Using this function
+ * when protected only by rcu_read_lock() will result in infrequent
+ * but very ugly failures.
+ */
+#define rcu_dereference_protected(p, c) \
+ __rcu_dereference_protected((p), (c), __rcu)
+
+
+/**
+ * rcu_dereference() - fetch RCU-protected pointer for dereferencing
+ * @p: The pointer to read, prior to dereferencing
+ *
+ * This is a simple wrapper around rcu_dereference_check().
+ */
+#define rcu_dereference(p) rcu_dereference_check(p, 0)
+
+/**
+ * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
+ * @p: The pointer to read, prior to dereferencing
+ *
+ * Makes rcu_dereference_check() do the dirty work.
+ */
+#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
+
+/**
+ * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
+ * @p: The pointer to read, prior to dereferencing
+ *
+ * Makes rcu_dereference_check() do the dirty work.
+ */
+#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
+
+/**
+ * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
+ * @p: The pointer to hand off
+ *
+ * This is simply an identity function, but it documents where a pointer
+ * is handed off from RCU to some other synchronization mechanism, for
+ * example, reference counting or locking. In C11, it would map to
+ * kill_dependency(). It could be used as follows:
+ *
+ * rcu_read_lock();
+ * p = rcu_dereference(gp);
+ * long_lived = is_long_lived(p);
+ * if (long_lived) {
+ * if (!atomic_inc_not_zero(p->refcnt))
+ * long_lived = false;
+ * else
+ * p = rcu_pointer_handoff(p);
+ * }
+ * rcu_read_unlock();
+ */
+#define rcu_pointer_handoff(p) (p)
+
+/**
+ * rcu_read_lock() - mark the beginning of an RCU read-side critical section
+ *
+ * When synchronize_rcu() is invoked on one CPU while other CPUs
+ * are within RCU read-side critical sections, then the
+ * synchronize_rcu() is guaranteed to block until after all the other
+ * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
+ * on one CPU while other CPUs are within RCU read-side critical
+ * sections, invocation of the corresponding RCU callback is deferred
+ * until after the all the other CPUs exit their critical sections.
+ *
+ * Note, however, that RCU callbacks are permitted to run concurrently
+ * with new RCU read-side critical sections. One way that this can happen
+ * is via the following sequence of events: (1) CPU 0 enters an RCU
+ * read-side critical section, (2) CPU 1 invokes call_rcu() to register
+ * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
+ * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
+ * callback is invoked. This is legal, because the RCU read-side critical
+ * section that was running concurrently with the call_rcu() (and which
+ * therefore might be referencing something that the corresponding RCU
+ * callback would free up) has completed before the corresponding
+ * RCU callback is invoked.
+ *
+ * RCU read-side critical sections may be nested. Any deferred actions
+ * will be deferred until the outermost RCU read-side critical section
+ * completes.
+ *
+ * You can avoid reading and understanding the next paragraph by
+ * following this rule: don't put anything in an rcu_read_lock() RCU
+ * read-side critical section that would block in a !PREEMPT kernel.
+ * But if you want the full story, read on!
+ *
+ * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
+ * it is illegal to block while in an RCU read-side critical section.
+ * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPT
+ * kernel builds, RCU read-side critical sections may be preempted,
+ * but explicit blocking is illegal. Finally, in preemptible RCU
+ * implementations in real-time (with -rt patchset) kernel builds, RCU
+ * read-side critical sections may be preempted and they may also block, but
+ * only when acquiring spinlocks that are subject to priority inheritance.
+ */
+static inline void rcu_read_lock(void)
+{
+ __rcu_read_lock();
+ __acquire(RCU);
+ rcu_lock_acquire(&rcu_lock_map);
+ RCU_LOCKDEP_WARN(!rcu_is_watching(),
+ "rcu_read_lock() used illegally while idle");
+}
+
+/*
+ * So where is rcu_write_lock()? It does not exist, as there is no
+ * way for writers to lock out RCU readers. This is a feature, not
+ * a bug -- this property is what provides RCU's performance benefits.
+ * Of course, writers must coordinate with each other. The normal
+ * spinlock primitives work well for this, but any other technique may be
+ * used as well. RCU does not care how the writers keep out of each
+ * others' way, as long as they do so.
+ */
+
+/**
+ * rcu_read_unlock() - marks the end of an RCU read-side critical section.
+ *
+ * In most situations, rcu_read_unlock() is immune from deadlock.
+ * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
+ * is responsible for deboosting, which it does via rt_mutex_unlock().
+ * Unfortunately, this function acquires the scheduler's runqueue and
+ * priority-inheritance spinlocks. This means that deadlock could result
+ * if the caller of rcu_read_unlock() already holds one of these locks or
+ * any lock that is ever acquired while holding them; or any lock which
+ * can be taken from interrupt context because rcu_boost()->rt_mutex_lock()
+ * does not disable irqs while taking ->wait_lock.
+ *
+ * That said, RCU readers are never priority boosted unless they were
+ * preempted. Therefore, one way to avoid deadlock is to make sure
+ * that preemption never happens within any RCU read-side critical
+ * section whose outermost rcu_read_unlock() is called with one of
+ * rt_mutex_unlock()'s locks held. Such preemption can be avoided in
+ * a number of ways, for example, by invoking preempt_disable() before
+ * critical section's outermost rcu_read_lock().
+ *
+ * Given that the set of locks acquired by rt_mutex_unlock() might change
+ * at any time, a somewhat more future-proofed approach is to make sure
+ * that that preemption never happens within any RCU read-side critical
+ * section whose outermost rcu_read_unlock() is called with irqs disabled.
+ * This approach relies on the fact that rt_mutex_unlock() currently only
+ * acquires irq-disabled locks.
+ *
+ * The second of these two approaches is best in most situations,
+ * however, the first approach can also be useful, at least to those
+ * developers willing to keep abreast of the set of locks acquired by
+ * rt_mutex_unlock().
+ *
+ * See rcu_read_lock() for more information.
+ */
+static inline void rcu_read_unlock(void)
+{
+ RCU_LOCKDEP_WARN(!rcu_is_watching(),
+ "rcu_read_unlock() used illegally while idle");
+ __release(RCU);
+ __rcu_read_unlock();
+ rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
+}
+
+/**
+ * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
+ *
+ * This is equivalent of rcu_read_lock(), but to be used when updates
+ * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
+ * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
+ * softirq handler to be a quiescent state, a process in RCU read-side
+ * critical section must be protected by disabling softirqs. Read-side
+ * critical sections in interrupt context can use just rcu_read_lock(),
+ * though this should at least be commented to avoid confusing people
+ * reading the code.
+ *
+ * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
+ * must occur in the same context, for example, it is illegal to invoke
+ * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
+ * was invoked from some other task.
+ */
+static inline void rcu_read_lock_bh(void)
+{
+ local_bh_disable();
+ __acquire(RCU_BH);
+ rcu_lock_acquire(&rcu_bh_lock_map);
+ RCU_LOCKDEP_WARN(!rcu_is_watching(),
+ "rcu_read_lock_bh() used illegally while idle");
+}
+
+/*
+ * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
+ *
+ * See rcu_read_lock_bh() for more information.
+ */
+static inline void rcu_read_unlock_bh(void)
+{
+ RCU_LOCKDEP_WARN(!rcu_is_watching(),
+ "rcu_read_unlock_bh() used illegally while idle");
+ rcu_lock_release(&rcu_bh_lock_map);
+ __release(RCU_BH);
+ local_bh_enable();
+}
+
+/**
+ * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
+ *
+ * This is equivalent of rcu_read_lock(), but to be used when updates
+ * are being done using call_rcu_sched() or synchronize_rcu_sched().
+ * Read-side critical sections can also be introduced by anything that
+ * disables preemption, including local_irq_disable() and friends.
+ *
+ * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
+ * must occur in the same context, for example, it is illegal to invoke
+ * rcu_read_unlock_sched() from process context if the matching
+ * rcu_read_lock_sched() was invoked from an NMI handler.
+ */
+static inline void rcu_read_lock_sched(void)
+{
+ preempt_disable();
+ __acquire(RCU_SCHED);
+ rcu_lock_acquire(&rcu_sched_lock_map);
+ RCU_LOCKDEP_WARN(!rcu_is_watching(),
+ "rcu_read_lock_sched() used illegally while idle");
+}
+
+/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
+static inline notrace void rcu_read_lock_sched_notrace(void)
+{
+ preempt_disable_notrace();
+ __acquire(RCU_SCHED);
+}
+
+/*
+ * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
+ *
+ * See rcu_read_lock_sched for more information.
+ */
+static inline void rcu_read_unlock_sched(void)
+{
+ RCU_LOCKDEP_WARN(!rcu_is_watching(),
+ "rcu_read_unlock_sched() used illegally while idle");
+ rcu_lock_release(&rcu_sched_lock_map);
+ __release(RCU_SCHED);
+ preempt_enable();
+}
+
+/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
+static inline notrace void rcu_read_unlock_sched_notrace(void)
+{
+ __release(RCU_SCHED);
+ preempt_enable_notrace();
+}
+
+/**
+ * RCU_INIT_POINTER() - initialize an RCU protected pointer
+ *
+ * Initialize an RCU-protected pointer in special cases where readers
+ * do not need ordering constraints on the CPU or the compiler. These
+ * special cases are:
+ *
+ * 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
+ * 2. The caller has taken whatever steps are required to prevent
+ * RCU readers from concurrently accessing this pointer -or-
+ * 3. The referenced data structure has already been exposed to
+ * readers either at compile time or via rcu_assign_pointer() -and-
+ * a. You have not made -any- reader-visible changes to
+ * this structure since then -or-
+ * b. It is OK for readers accessing this structure from its
+ * new location to see the old state of the structure. (For
+ * example, the changes were to statistical counters or to
+ * other state where exact synchronization is not required.)
+ *
+ * Failure to follow these rules governing use of RCU_INIT_POINTER() will
+ * result in impossible-to-diagnose memory corruption. As in the structures
+ * will look OK in crash dumps, but any concurrent RCU readers might
+ * see pre-initialized values of the referenced data structure. So
+ * please be very careful how you use RCU_INIT_POINTER()!!!
+ *
+ * If you are creating an RCU-protected linked structure that is accessed
+ * by a single external-to-structure RCU-protected pointer, then you may
+ * use RCU_INIT_POINTER() to initialize the internal RCU-protected
+ * pointers, but you must use rcu_assign_pointer() to initialize the
+ * external-to-structure pointer -after- you have completely initialized
+ * the reader-accessible portions of the linked structure.
+ *
+ * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
+ * ordering guarantees for either the CPU or the compiler.
+ */
+#define RCU_INIT_POINTER(p, v) \
+ do { \
+ rcu_dereference_sparse(p, __rcu); \
+ WRITE_ONCE(p, RCU_INITIALIZER(v)); \
+ } while (0)
+
+/**
+ * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
+ *
+ * GCC-style initialization for an RCU-protected pointer in a structure field.
+ */
+#define RCU_POINTER_INITIALIZER(p, v) \
+ .p = RCU_INITIALIZER(v)
+
+/*
+ * Does the specified offset indicate that the corresponding rcu_head
+ * structure can be handled by kfree_rcu()?
+ */
+#define __is_kfree_rcu_offset(offset) ((offset) < 4096)
+
+/*
+ * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
+ */
+#define __kfree_rcu(head, offset) \
+ do { \
+ BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
+ kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
+ } while (0)
+
+/**
+ * kfree_rcu() - kfree an object after a grace period.
+ * @ptr: pointer to kfree
+ * @rcu_head: the name of the struct rcu_head within the type of @ptr.
+ *
+ * Many rcu callbacks functions just call kfree() on the base structure.
+ * These functions are trivial, but their size adds up, and furthermore
+ * when they are used in a kernel module, that module must invoke the
+ * high-latency rcu_barrier() function at module-unload time.
+ *
+ * The kfree_rcu() function handles this issue. Rather than encoding a
+ * function address in the embedded rcu_head structure, kfree_rcu() instead
+ * encodes the offset of the rcu_head structure within the base structure.
+ * Because the functions are not allowed in the low-order 4096 bytes of
+ * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
+ * If the offset is larger than 4095 bytes, a compile-time error will
+ * be generated in __kfree_rcu(). If this error is triggered, you can
+ * either fall back to use of call_rcu() or rearrange the structure to
+ * position the rcu_head structure into the first 4096 bytes.
+ *
+ * Note that the allowable offset might decrease in the future, for example,
+ * to allow something like kmem_cache_free_rcu().
+ *
+ * The BUILD_BUG_ON check must not involve any function calls, hence the
+ * checks are done in macros here.
+ */
+#define kfree_rcu(ptr, rcu_head) \
+ __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
+
+#ifdef CONFIG_TINY_RCU
+static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt)
+{
+ *nextevt = KTIME_MAX;
+ return 0;
+}
+#endif /* #ifdef CONFIG_TINY_RCU */
+
+#if defined(CONFIG_RCU_NOCB_CPU_ALL)
+static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
+#elif defined(CONFIG_RCU_NOCB_CPU)
+bool rcu_is_nocb_cpu(int cpu);
+#else
+static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
+#endif
+
+
+/* Only for use by adaptive-ticks code. */
+#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
+bool rcu_sys_is_idle(void);
+void rcu_sysidle_force_exit(void);
+#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
+
+static inline bool rcu_sys_is_idle(void)
+{
+ return false;
+}
+
+static inline void rcu_sysidle_force_exit(void)
+{
+}
+
+#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
+
+
+#endif /* __LINUX_RCUPDATE_H */