0,0 → 1,1158 |
/* |
* 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 <asm/barrier.h> |
|
extern int rcu_expedited; /* for sysctl */ |
|
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, |
void (*func)(struct rcu_head *head)); |
|
#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, |
void (*func)(struct rcu_head *head)); |
|
/** |
* 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, |
void (*func)(struct rcu_head *rcu)); |
|
void synchronize_sched(void); |
|
/** |
* 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, void (*func)(struct rcu_head *head)); |
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) |
{ |
preempt_disable(); |
} |
|
static inline void __rcu_read_unlock(void) |
{ |
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_sched_qs(void); |
void rcu_bh_qs(void); |
void rcu_check_callbacks(int user); |
struct notifier_block; |
void rcu_idle_enter(void); |
void rcu_idle_exit(void); |
void rcu_irq_enter(void); |
void rcu_irq_exit(void); |
|
#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_RCU_USER_QS |
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_RCU_USER_QS */ |
|
#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 { \ |
if (ACCESS_ONCE((t)->rcu_tasks_holdout)) \ |
ACCESS_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) do { } while (0) |
#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. |
*/ |
|
typedef void call_rcu_func_t(struct rcu_head *head, |
void (*func)(struct rcu_head *head)); |
void wait_rcu_gp(call_rcu_func_t crf); |
|
#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. Note that disabling |
* of preemption (including disabling irqs) counts as an RCU-sched |
* read-side critical section. This is useful for debug checks in functions |
* that required that they be called within an RCU-sched read-side |
* critical section. |
* |
* Check debug_lockdep_rcu_enabled() to prevent false positives during boot |
* and while lockdep is disabled. |
* |
* Note that if the CPU is in the idle loop from an RCU point of |
* view (ie: that we are in the section between rcu_idle_enter() and |
* rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU |
* did an rcu_read_lock(). The reason for this is that RCU ignores CPUs |
* that are in such a section, considering these as in extended quiescent |
* state, so such a CPU is effectively never in an RCU read-side critical |
* section regardless of what RCU primitives it invokes. This state of |
* affairs is required --- we need to keep an RCU-free window in idle |
* where the CPU may possibly enter into low power mode. This way we can |
* notice an extended quiescent state to other CPUs that started a grace |
* period. Otherwise we would delay any grace period as long as we run in |
* the idle task. |
* |
* Similarly, we avoid claiming an SRCU read lock held if the current |
* CPU is offline. |
*/ |
#ifdef CONFIG_PREEMPT_COUNT |
static inline int rcu_read_lock_sched_held(void) |
{ |
int lockdep_opinion = 0; |
|
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 || 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 */ |
|
#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_assert - emit lockdep splat if specified condition not met |
* @c: condition to check |
* @s: informative message |
*/ |
#define rcu_lockdep_assert(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_assert(!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_assert(!lock_is_held(&rcu_bh_lock_map), \ |
"Illegal context switch in RCU-bh read-side critical section"); \ |
rcu_lockdep_assert(!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_assert(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)ACCESS_ONCE(p); \ |
rcu_dereference_sparse(p, space); \ |
((typeof(*p) __force __kernel *)(_________p1)); \ |
}) |
#define __rcu_dereference_check(p, c, space) \ |
({ \ |
typeof(*p) *_________p1 = (typeof(*p) *__force)ACCESS_ONCE(p); \ |
rcu_lockdep_assert(c, "suspicious rcu_dereference_check() usage"); \ |
rcu_dereference_sparse(p, space); \ |
smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ |
((typeof(*p) __force __kernel *)(_________p1)); \ |
}) |
#define __rcu_dereference_protected(p, c, space) \ |
({ \ |
rcu_lockdep_assert(c, "suspicious rcu_dereference_protected() usage"); \ |
rcu_dereference_sparse(p, space); \ |
((typeof(*p) __force __kernel *)(p)); \ |
}) |
|
#define __rcu_access_index(p, space) \ |
({ \ |
typeof(p) _________p1 = ACCESS_ONCE(p); \ |
rcu_dereference_sparse(p, space); \ |
(_________p1); \ |
}) |
#define __rcu_dereference_index_check(p, c) \ |
({ \ |
typeof(p) _________p1 = ACCESS_ONCE(p); \ |
rcu_lockdep_assert(c, \ |
"suspicious rcu_dereference_index_check() usage"); \ |
smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ |
(_________p1); \ |
}) |
|
/** |
* 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) |
|
/** |
* lockless_dereference() - safely load a pointer for later dereference |
* @p: The pointer to load |
* |
* Similar to rcu_dereference(), but for situations where the pointed-to |
* object's lifetime is managed by something other than RCU. That |
* "something other" might be reference counting or simple immortality. |
*/ |
#define lockless_dereference(p) \ |
({ \ |
typeof(p) _________p1 = ACCESS_ONCE(p); \ |
smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ |
(_________p1); \ |
}) |
|
/** |
* 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 ACCESS_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), rcu_read_lock_held() || (c), __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), rcu_read_lock_bh_held() || (c), __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), rcu_read_lock_sched_held() || (c), \ |
__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_access_index() - fetch RCU index with no dereferencing |
* @p: The index to read |
* |
* Return the value of the specified RCU-protected index, but omit the |
* smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful |
* when the value of this index is accessed, but the index is not |
* dereferenced, for example, when testing an RCU-protected index against |
* -1. Although rcu_access_index() may also be used in cases where |
* update-side locks prevent the value of the index from changing, you |
* should instead use rcu_dereference_index_protected() for this use case. |
*/ |
#define rcu_access_index(p) __rcu_access_index((p), __rcu) |
|
/** |
* rcu_dereference_index_check() - rcu_dereference for indices with debug checking |
* @p: The pointer to read, prior to dereferencing |
* @c: The conditions under which the dereference will take place |
* |
* Similar to rcu_dereference_check(), but omits the sparse checking. |
* This allows rcu_dereference_index_check() to be used on integers, |
* which can then be used as array indices. Attempting to use |
* rcu_dereference_check() on an integer will give compiler warnings |
* because the sparse address-space mechanism relies on dereferencing |
* the RCU-protected pointer. Dereferencing integers is not something |
* that even gcc will put up with. |
* |
* Note that this function does not implicitly check for RCU read-side |
* critical sections. If this function gains lots of uses, it might |
* make sense to provide versions for each flavor of RCU, but it does |
* not make sense as of early 2010. |
*/ |
#define rcu_dereference_index_check(p, c) \ |
__rcu_dereference_index_check((p), (c)) |
|
/** |
* 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 ACCESS_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_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_assert(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_assert(rcu_is_watching(), |
"rcu_read_unlock() used illegally while idle"); |
rcu_lock_release(&rcu_lock_map); |
__release(RCU); |
__rcu_read_unlock(); |
} |
|
/** |
* 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_assert(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_assert(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_assert(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_assert(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); \ |
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, (void (*)(struct rcu_head *))(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)) |
|
#if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL) |
static inline int rcu_needs_cpu(unsigned long *delta_jiffies) |
{ |
*delta_jiffies = ULONG_MAX; |
return 0; |
} |
#endif /* #if defined(CONFIG_TINY_RCU) || defined(CONFIG_RCU_NOCB_CPU_ALL) */ |
|
#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 */ |