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  1. /*
  2.  * Read-Copy Update mechanism for mutual exclusion
  3.  *
  4.  * This program is free software; you can redistribute it and/or modify
  5.  * it under the terms of the GNU General Public License as published by
  6.  * the Free Software Foundation; either version 2 of the License, or
  7.  * (at your option) any later version.
  8.  *
  9.  * This program is distributed in the hope that it will be useful,
  10.  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11.  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12.  * GNU General Public License for more details.
  13.  *
  14.  * You should have received a copy of the GNU General Public License
  15.  * along with this program; if not, you can access it online at
  16.  * http://www.gnu.org/licenses/gpl-2.0.html.
  17.  *
  18.  * Copyright IBM Corporation, 2001
  19.  *
  20.  * Author: Dipankar Sarma <dipankar@in.ibm.com>
  21.  *
  22.  * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
  23.  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
  24.  * Papers:
  25.  * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
  26.  * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
  27.  *
  28.  * For detailed explanation of Read-Copy Update mechanism see -
  29.  *              http://lse.sourceforge.net/locking/rcupdate.html
  30.  *
  31.  */
  32.  
  33. #ifndef __LINUX_RCUPDATE_H
  34. #define __LINUX_RCUPDATE_H
  35.  
  36. #include <linux/types.h>
  37. #include <linux/cache.h>
  38. #include <linux/spinlock.h>
  39. #include <linux/threads.h>
  40. //#include <linux/cpumask.h>
  41. #include <linux/seqlock.h>
  42. #include <linux/lockdep.h>
  43. #include <linux/completion.h>
  44. //#include <linux/debugobjects.h>
  45. #include <linux/bug.h>
  46. #include <linux/compiler.h>
  47. #include <linux/ktime.h>
  48.  
  49. #include <asm/barrier.h>
  50.  
  51. #ifndef CONFIG_TINY_RCU
  52. extern int rcu_expedited; /* for sysctl */
  53. extern int rcu_normal;    /* also for sysctl */
  54. #endif /* #ifndef CONFIG_TINY_RCU */
  55.  
  56. #ifdef CONFIG_TINY_RCU
  57. /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
  58. static inline bool rcu_gp_is_normal(void)  /* Internal RCU use. */
  59. {
  60.         return true;
  61. }
  62. static inline bool rcu_gp_is_expedited(void)  /* Internal RCU use. */
  63. {
  64.         return false;
  65. }
  66.  
  67. static inline void rcu_expedite_gp(void)
  68. {
  69. }
  70.  
  71. static inline void rcu_unexpedite_gp(void)
  72. {
  73. }
  74. #else /* #ifdef CONFIG_TINY_RCU */
  75. bool rcu_gp_is_normal(void);     /* Internal RCU use. */
  76. bool rcu_gp_is_expedited(void);  /* Internal RCU use. */
  77. void rcu_expedite_gp(void);
  78. void rcu_unexpedite_gp(void);
  79. #endif /* #else #ifdef CONFIG_TINY_RCU */
  80.  
  81. enum rcutorture_type {
  82.         RCU_FLAVOR,
  83.         RCU_BH_FLAVOR,
  84.         RCU_SCHED_FLAVOR,
  85.         RCU_TASKS_FLAVOR,
  86.         SRCU_FLAVOR,
  87.         INVALID_RCU_FLAVOR
  88. };
  89.  
  90. #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
  91. void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
  92.                             unsigned long *gpnum, unsigned long *completed);
  93. void rcutorture_record_test_transition(void);
  94. void rcutorture_record_progress(unsigned long vernum);
  95. void do_trace_rcu_torture_read(const char *rcutorturename,
  96.                                struct rcu_head *rhp,
  97.                                unsigned long secs,
  98.                                unsigned long c_old,
  99.                                unsigned long c);
  100. #else
  101. static inline void rcutorture_get_gp_data(enum rcutorture_type test_type,
  102.                                           int *flags,
  103.                                           unsigned long *gpnum,
  104.                                           unsigned long *completed)
  105. {
  106.         *flags = 0;
  107.         *gpnum = 0;
  108.         *completed = 0;
  109. }
  110. static inline void rcutorture_record_test_transition(void)
  111. {
  112. }
  113. static inline void rcutorture_record_progress(unsigned long vernum)
  114. {
  115. }
  116. #ifdef CONFIG_RCU_TRACE
  117. void do_trace_rcu_torture_read(const char *rcutorturename,
  118.                                struct rcu_head *rhp,
  119.                                unsigned long secs,
  120.                                unsigned long c_old,
  121.                                unsigned long c);
  122. #else
  123. #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
  124.         do { } while (0)
  125. #endif
  126. #endif
  127.  
  128. #define UINT_CMP_GE(a, b)       (UINT_MAX / 2 >= (a) - (b))
  129. #define UINT_CMP_LT(a, b)       (UINT_MAX / 2 < (a) - (b))
  130. #define ULONG_CMP_GE(a, b)      (ULONG_MAX / 2 >= (a) - (b))
  131. #define ULONG_CMP_LT(a, b)      (ULONG_MAX / 2 < (a) - (b))
  132. #define ulong2long(a)           (*(long *)(&(a)))
  133.  
  134. /* Exported common interfaces */
  135.  
  136. #ifdef CONFIG_PREEMPT_RCU
  137.  
  138. /**
  139.  * call_rcu() - Queue an RCU callback for invocation after a grace period.
  140.  * @head: structure to be used for queueing the RCU updates.
  141.  * @func: actual callback function to be invoked after the grace period
  142.  *
  143.  * The callback function will be invoked some time after a full grace
  144.  * period elapses, in other words after all pre-existing RCU read-side
  145.  * critical sections have completed.  However, the callback function
  146.  * might well execute concurrently with RCU read-side critical sections
  147.  * that started after call_rcu() was invoked.  RCU read-side critical
  148.  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
  149.  * and may be nested.
  150.  *
  151.  * Note that all CPUs must agree that the grace period extended beyond
  152.  * all pre-existing RCU read-side critical section.  On systems with more
  153.  * than one CPU, this means that when "func()" is invoked, each CPU is
  154.  * guaranteed to have executed a full memory barrier since the end of its
  155.  * last RCU read-side critical section whose beginning preceded the call
  156.  * to call_rcu().  It also means that each CPU executing an RCU read-side
  157.  * critical section that continues beyond the start of "func()" must have
  158.  * executed a memory barrier after the call_rcu() but before the beginning
  159.  * of that RCU read-side critical section.  Note that these guarantees
  160.  * include CPUs that are offline, idle, or executing in user mode, as
  161.  * well as CPUs that are executing in the kernel.
  162.  *
  163.  * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
  164.  * resulting RCU callback function "func()", then both CPU A and CPU B are
  165.  * guaranteed to execute a full memory barrier during the time interval
  166.  * between the call to call_rcu() and the invocation of "func()" -- even
  167.  * if CPU A and CPU B are the same CPU (but again only if the system has
  168.  * more than one CPU).
  169.  */
  170. void call_rcu(struct rcu_head *head,
  171.               rcu_callback_t func);
  172.  
  173. #else /* #ifdef CONFIG_PREEMPT_RCU */
  174.  
  175. /* In classic RCU, call_rcu() is just call_rcu_sched(). */
  176. #define call_rcu        call_rcu_sched
  177.  
  178. #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
  179.  
  180. /**
  181.  * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
  182.  * @head: structure to be used for queueing the RCU updates.
  183.  * @func: actual callback function to be invoked after the grace period
  184.  *
  185.  * The callback function will be invoked some time after a full grace
  186.  * period elapses, in other words after all currently executing RCU
  187.  * read-side critical sections have completed. call_rcu_bh() assumes
  188.  * that the read-side critical sections end on completion of a softirq
  189.  * handler. This means that read-side critical sections in process
  190.  * context must not be interrupted by softirqs. This interface is to be
  191.  * used when most of the read-side critical sections are in softirq context.
  192.  * RCU read-side critical sections are delimited by :
  193.  *  - rcu_read_lock() and  rcu_read_unlock(), if in interrupt context.
  194.  *  OR
  195.  *  - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
  196.  *  These may be nested.
  197.  *
  198.  * See the description of call_rcu() for more detailed information on
  199.  * memory ordering guarantees.
  200.  */
  201. void call_rcu_bh(struct rcu_head *head,
  202.                  rcu_callback_t func);
  203.  
  204. /**
  205.  * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
  206.  * @head: structure to be used for queueing the RCU updates.
  207.  * @func: actual callback function to be invoked after the grace period
  208.  *
  209.  * The callback function will be invoked some time after a full grace
  210.  * period elapses, in other words after all currently executing RCU
  211.  * read-side critical sections have completed. call_rcu_sched() assumes
  212.  * that the read-side critical sections end on enabling of preemption
  213.  * or on voluntary preemption.
  214.  * RCU read-side critical sections are delimited by :
  215.  *  - rcu_read_lock_sched() and  rcu_read_unlock_sched(),
  216.  *  OR
  217.  *  anything that disables preemption.
  218.  *  These may be nested.
  219.  *
  220.  * See the description of call_rcu() for more detailed information on
  221.  * memory ordering guarantees.
  222.  */
  223. void call_rcu_sched(struct rcu_head *head,
  224.                     rcu_callback_t func);
  225.  
  226. void synchronize_sched(void);
  227.  
  228. #define wait_rcu_gp(...)
  229. /**
  230.  * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
  231.  * @head: structure to be used for queueing the RCU updates.
  232.  * @func: actual callback function to be invoked after the grace period
  233.  *
  234.  * The callback function will be invoked some time after a full grace
  235.  * period elapses, in other words after all currently executing RCU
  236.  * read-side critical sections have completed. call_rcu_tasks() assumes
  237.  * that the read-side critical sections end at a voluntary context
  238.  * switch (not a preemption!), entry into idle, or transition to usermode
  239.  * execution.  As such, there are no read-side primitives analogous to
  240.  * rcu_read_lock() and rcu_read_unlock() because this primitive is intended
  241.  * to determine that all tasks have passed through a safe state, not so
  242.  * much for data-strcuture synchronization.
  243.  *
  244.  * See the description of call_rcu() for more detailed information on
  245.  * memory ordering guarantees.
  246.  */
  247. void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
  248. void synchronize_rcu_tasks(void);
  249. void rcu_barrier_tasks(void);
  250.  
  251. #ifdef CONFIG_PREEMPT_RCU
  252.  
  253. void __rcu_read_lock(void);
  254. void __rcu_read_unlock(void);
  255. void rcu_read_unlock_special(struct task_struct *t);
  256. void synchronize_rcu(void);
  257.  
  258. /*
  259.  * Defined as a macro as it is a very low level header included from
  260.  * areas that don't even know about current.  This gives the rcu_read_lock()
  261.  * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
  262.  * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
  263.  */
  264. #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
  265.  
  266. #else /* #ifdef CONFIG_PREEMPT_RCU */
  267.  
  268. static inline void __rcu_read_lock(void)
  269. {
  270.         if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
  271.                 preempt_disable();
  272. }
  273.  
  274. static inline void __rcu_read_unlock(void)
  275. {
  276.         if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
  277.                 preempt_enable();
  278. }
  279.  
  280. static inline void synchronize_rcu(void)
  281. {
  282.         synchronize_sched();
  283. }
  284.  
  285. static inline int rcu_preempt_depth(void)
  286. {
  287.         return 0;
  288. }
  289.  
  290. #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
  291.  
  292. /* Internal to kernel */
  293. void rcu_init(void);
  294. void rcu_sched_qs(void);
  295. void rcu_bh_qs(void);
  296. void rcu_check_callbacks(int user);
  297. void rcu_report_dead(unsigned int cpu);
  298.  
  299. #ifndef CONFIG_TINY_RCU
  300. void rcu_end_inkernel_boot(void);
  301. #else /* #ifndef CONFIG_TINY_RCU */
  302. static inline void rcu_end_inkernel_boot(void) { }
  303. #endif /* #ifndef CONFIG_TINY_RCU */
  304.  
  305. #ifdef CONFIG_RCU_STALL_COMMON
  306. void rcu_sysrq_start(void);
  307. void rcu_sysrq_end(void);
  308. #else /* #ifdef CONFIG_RCU_STALL_COMMON */
  309. static inline void rcu_sysrq_start(void)
  310. {
  311. }
  312. static inline void rcu_sysrq_end(void)
  313. {
  314. }
  315. #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
  316.  
  317. #ifdef CONFIG_NO_HZ_FULL
  318. void rcu_user_enter(void);
  319. void rcu_user_exit(void);
  320. #else
  321. static inline void rcu_user_enter(void) { }
  322. static inline void rcu_user_exit(void) { }
  323. #endif /* CONFIG_NO_HZ_FULL */
  324.  
  325. #ifdef CONFIG_RCU_NOCB_CPU
  326. void rcu_init_nohz(void);
  327. #else /* #ifdef CONFIG_RCU_NOCB_CPU */
  328. static inline void rcu_init_nohz(void)
  329. {
  330. }
  331. #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
  332.  
  333. /**
  334.  * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
  335.  * @a: Code that RCU needs to pay attention to.
  336.  *
  337.  * RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
  338.  * in the inner idle loop, that is, between the rcu_idle_enter() and
  339.  * the rcu_idle_exit() -- RCU will happily ignore any such read-side
  340.  * critical sections.  However, things like powertop need tracepoints
  341.  * in the inner idle loop.
  342.  *
  343.  * This macro provides the way out:  RCU_NONIDLE(do_something_with_RCU())
  344.  * will tell RCU that it needs to pay attending, invoke its argument
  345.  * (in this example, a call to the do_something_with_RCU() function),
  346.  * and then tell RCU to go back to ignoring this CPU.  It is permissible
  347.  * to nest RCU_NONIDLE() wrappers, but the nesting level is currently
  348.  * quite limited.  If deeper nesting is required, it will be necessary
  349.  * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
  350.  */
  351. #define RCU_NONIDLE(a) \
  352.         do { \
  353.                 rcu_irq_enter_irqson(); \
  354.                 do { a; } while (0); \
  355.                 rcu_irq_exit_irqson(); \
  356.         } while (0)
  357.  
  358. /*
  359.  * Note a voluntary context switch for RCU-tasks benefit.  This is a
  360.  * macro rather than an inline function to avoid #include hell.
  361.  */
  362. #ifdef CONFIG_TASKS_RCU
  363. #define TASKS_RCU(x) x
  364. extern struct srcu_struct tasks_rcu_exit_srcu;
  365. #define rcu_note_voluntary_context_switch(t) \
  366.         do { \
  367.                 rcu_all_qs(); \
  368.                 if (READ_ONCE((t)->rcu_tasks_holdout)) \
  369.                         WRITE_ONCE((t)->rcu_tasks_holdout, false); \
  370.         } while (0)
  371. #else /* #ifdef CONFIG_TASKS_RCU */
  372. #define TASKS_RCU(x) do { } while (0)
  373. #define rcu_note_voluntary_context_switch(t)    rcu_all_qs()
  374. #endif /* #else #ifdef CONFIG_TASKS_RCU */
  375.  
  376. /**
  377.  * cond_resched_rcu_qs - Report potential quiescent states to RCU
  378.  *
  379.  * This macro resembles cond_resched(), except that it is defined to
  380.  * report potential quiescent states to RCU-tasks even if the cond_resched()
  381.  * machinery were to be shut off, as some advocate for PREEMPT kernels.
  382.  */
  383. #define cond_resched_rcu_qs() \
  384. do { \
  385.         if (!cond_resched()) \
  386.                 rcu_note_voluntary_context_switch(current); \
  387. } while (0)
  388.  
  389. #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP)
  390. bool __rcu_is_watching(void);
  391. #endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) || defined(CONFIG_SMP) */
  392.  
  393. /*
  394.  * Infrastructure to implement the synchronize_() primitives in
  395.  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
  396.  */
  397.  
  398. #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
  399. #include <linux/rcutree.h>
  400. #elif defined(CONFIG_TINY_RCU)
  401. #include <linux/rcutiny.h>
  402. #else
  403. #error "Unknown RCU implementation specified to kernel configuration"
  404. #endif
  405.  
  406. /*
  407.  * init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
  408.  * initialization and destruction of rcu_head on the stack. rcu_head structures
  409.  * allocated dynamically in the heap or defined statically don't need any
  410.  * initialization.
  411.  */
  412. #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
  413. void init_rcu_head(struct rcu_head *head);
  414. void destroy_rcu_head(struct rcu_head *head);
  415. void init_rcu_head_on_stack(struct rcu_head *head);
  416. void destroy_rcu_head_on_stack(struct rcu_head *head);
  417. #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
  418. static inline void init_rcu_head(struct rcu_head *head)
  419. {
  420. }
  421.  
  422. static inline void destroy_rcu_head(struct rcu_head *head)
  423. {
  424. }
  425.  
  426. static inline void init_rcu_head_on_stack(struct rcu_head *head)
  427. {
  428. }
  429.  
  430. static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
  431. {
  432. }
  433. #endif  /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
  434.  
  435. #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
  436. bool rcu_lockdep_current_cpu_online(void);
  437. #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
  438. static inline bool rcu_lockdep_current_cpu_online(void)
  439. {
  440.         return true;
  441. }
  442. #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
  443.  
  444. #ifdef CONFIG_DEBUG_LOCK_ALLOC
  445.  
  446. static inline void rcu_lock_acquire(struct lockdep_map *map)
  447. {
  448.         lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
  449. }
  450.  
  451. static inline void rcu_lock_release(struct lockdep_map *map)
  452. {
  453.         lock_release(map, 1, _THIS_IP_);
  454. }
  455.  
  456. extern struct lockdep_map rcu_lock_map;
  457. extern struct lockdep_map rcu_bh_lock_map;
  458. extern struct lockdep_map rcu_sched_lock_map;
  459. extern struct lockdep_map rcu_callback_map;
  460. int debug_lockdep_rcu_enabled(void);
  461.  
  462. int rcu_read_lock_held(void);
  463. int rcu_read_lock_bh_held(void);
  464.  
  465. /**
  466.  * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
  467.  *
  468.  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
  469.  * RCU-sched read-side critical section.  In absence of
  470.  * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
  471.  * critical section unless it can prove otherwise.
  472.  */
  473. #ifdef CONFIG_PREEMPT_COUNT
  474. int rcu_read_lock_sched_held(void);
  475. #else /* #ifdef CONFIG_PREEMPT_COUNT */
  476. static inline int rcu_read_lock_sched_held(void)
  477. {
  478.         return 1;
  479. }
  480. #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
  481.  
  482. #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  483.  
  484. # define rcu_lock_acquire(a)            do { } while (0)
  485. # define rcu_lock_release(a)            do { } while (0)
  486.  
  487. static inline int rcu_read_lock_held(void)
  488. {
  489.         return 1;
  490. }
  491.  
  492. static inline int rcu_read_lock_bh_held(void)
  493. {
  494.         return 1;
  495. }
  496.  
  497. #ifdef CONFIG_PREEMPT_COUNT
  498. static inline int rcu_read_lock_sched_held(void)
  499. {
  500.         return preempt_count() != 0 || irqs_disabled();
  501. }
  502. #else /* #ifdef CONFIG_PREEMPT_COUNT */
  503. static inline int rcu_read_lock_sched_held(void)
  504. {
  505.         return 1;
  506. }
  507. #endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
  508.  
  509. #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
  510.  
  511. #ifdef CONFIG_PROVE_RCU
  512.  
  513. /**
  514.  * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
  515.  * @c: condition to check
  516.  * @s: informative message
  517.  */
  518. #define RCU_LOCKDEP_WARN(c, s)                                          \
  519.         do {                                                            \
  520.                 static bool __section(.data.unlikely) __warned;         \
  521.                 if (debug_lockdep_rcu_enabled() && !__warned && (c)) {  \
  522.                         __warned = true;                                \
  523.                         lockdep_rcu_suspicious(__FILE__, __LINE__, s);  \
  524.                 }                                                       \
  525.         } while (0)
  526.  
  527. #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
  528. static inline void rcu_preempt_sleep_check(void)
  529. {
  530.         RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
  531.                          "Illegal context switch in RCU read-side critical section");
  532. }
  533. #else /* #ifdef CONFIG_PROVE_RCU */
  534. static inline void rcu_preempt_sleep_check(void)
  535. {
  536. }
  537. #endif /* #else #ifdef CONFIG_PROVE_RCU */
  538.  
  539. #define rcu_sleep_check()                                               \
  540.         do {                                                            \
  541.                 rcu_preempt_sleep_check();                              \
  542.                 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),        \
  543.                                  "Illegal context switch in RCU-bh read-side critical section"); \
  544.                 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map),     \
  545.                                  "Illegal context switch in RCU-sched read-side critical section"); \
  546.         } while (0)
  547.  
  548. #else /* #ifdef CONFIG_PROVE_RCU */
  549.  
  550. #define RCU_LOCKDEP_WARN(c, s) do { } while (0)
  551. #define rcu_sleep_check() do { } while (0)
  552.  
  553. #endif /* #else #ifdef CONFIG_PROVE_RCU */
  554.  
  555. /*
  556.  * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
  557.  * and rcu_assign_pointer().  Some of these could be folded into their
  558.  * callers, but they are left separate in order to ease introduction of
  559.  * multiple flavors of pointers to match the multiple flavors of RCU
  560.  * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
  561.  * the future.
  562.  */
  563.  
  564. #ifdef __CHECKER__
  565. #define rcu_dereference_sparse(p, space) \
  566.         ((void)(((typeof(*p) space *)p) == p))
  567. #else /* #ifdef __CHECKER__ */
  568. #define rcu_dereference_sparse(p, space)
  569. #endif /* #else #ifdef __CHECKER__ */
  570.  
  571. #define __rcu_access_pointer(p, space) \
  572. ({ \
  573.         typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
  574.         rcu_dereference_sparse(p, space); \
  575.         ((typeof(*p) __force __kernel *)(_________p1)); \
  576. })
  577. #define __rcu_dereference_check(p, c, space) \
  578. ({ \
  579.         /* Dependency order vs. p above. */ \
  580.         typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
  581.         RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
  582.         rcu_dereference_sparse(p, space); \
  583.         ((typeof(*p) __force __kernel *)(________p1)); \
  584. })
  585. #define __rcu_dereference_protected(p, c, space) \
  586. ({ \
  587.         RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
  588.         rcu_dereference_sparse(p, space); \
  589.         ((typeof(*p) __force __kernel *)(p)); \
  590. })
  591.  
  592. /**
  593.  * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
  594.  * @v: The value to statically initialize with.
  595.  */
  596. #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
  597.  
  598. /**
  599.  * rcu_assign_pointer() - assign to RCU-protected pointer
  600.  * @p: pointer to assign to
  601.  * @v: value to assign (publish)
  602.  *
  603.  * Assigns the specified value to the specified RCU-protected
  604.  * pointer, ensuring that any concurrent RCU readers will see
  605.  * any prior initialization.
  606.  *
  607.  * Inserts memory barriers on architectures that require them
  608.  * (which is most of them), and also prevents the compiler from
  609.  * reordering the code that initializes the structure after the pointer
  610.  * assignment.  More importantly, this call documents which pointers
  611.  * will be dereferenced by RCU read-side code.
  612.  *
  613.  * In some special cases, you may use RCU_INIT_POINTER() instead
  614.  * of rcu_assign_pointer().  RCU_INIT_POINTER() is a bit faster due
  615.  * to the fact that it does not constrain either the CPU or the compiler.
  616.  * That said, using RCU_INIT_POINTER() when you should have used
  617.  * rcu_assign_pointer() is a very bad thing that results in
  618.  * impossible-to-diagnose memory corruption.  So please be careful.
  619.  * See the RCU_INIT_POINTER() comment header for details.
  620.  *
  621.  * Note that rcu_assign_pointer() evaluates each of its arguments only
  622.  * once, appearances notwithstanding.  One of the "extra" evaluations
  623.  * is in typeof() and the other visible only to sparse (__CHECKER__),
  624.  * neither of which actually execute the argument.  As with most cpp
  625.  * macros, this execute-arguments-only-once property is important, so
  626.  * please be careful when making changes to rcu_assign_pointer() and the
  627.  * other macros that it invokes.
  628.  */
  629. #define rcu_assign_pointer(p, v) smp_store_release(&p, RCU_INITIALIZER(v))
  630.  
  631. /**
  632.  * rcu_access_pointer() - fetch RCU pointer with no dereferencing
  633.  * @p: The pointer to read
  634.  *
  635.  * Return the value of the specified RCU-protected pointer, but omit the
  636.  * smp_read_barrier_depends() and keep the READ_ONCE().  This is useful
  637.  * when the value of this pointer is accessed, but the pointer is not
  638.  * dereferenced, for example, when testing an RCU-protected pointer against
  639.  * NULL.  Although rcu_access_pointer() may also be used in cases where
  640.  * update-side locks prevent the value of the pointer from changing, you
  641.  * should instead use rcu_dereference_protected() for this use case.
  642.  *
  643.  * It is also permissible to use rcu_access_pointer() when read-side
  644.  * access to the pointer was removed at least one grace period ago, as
  645.  * is the case in the context of the RCU callback that is freeing up
  646.  * the data, or after a synchronize_rcu() returns.  This can be useful
  647.  * when tearing down multi-linked structures after a grace period
  648.  * has elapsed.
  649.  */
  650. #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
  651.  
  652. /**
  653.  * rcu_dereference_check() - rcu_dereference with debug checking
  654.  * @p: The pointer to read, prior to dereferencing
  655.  * @c: The conditions under which the dereference will take place
  656.  *
  657.  * Do an rcu_dereference(), but check that the conditions under which the
  658.  * dereference will take place are correct.  Typically the conditions
  659.  * indicate the various locking conditions that should be held at that
  660.  * point.  The check should return true if the conditions are satisfied.
  661.  * An implicit check for being in an RCU read-side critical section
  662.  * (rcu_read_lock()) is included.
  663.  *
  664.  * For example:
  665.  *
  666.  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
  667.  *
  668.  * could be used to indicate to lockdep that foo->bar may only be dereferenced
  669.  * if either rcu_read_lock() is held, or that the lock required to replace
  670.  * the bar struct at foo->bar is held.
  671.  *
  672.  * Note that the list of conditions may also include indications of when a lock
  673.  * need not be held, for example during initialisation or destruction of the
  674.  * target struct:
  675.  *
  676.  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
  677.  *                                            atomic_read(&foo->usage) == 0);
  678.  *
  679.  * Inserts memory barriers on architectures that require them
  680.  * (currently only the Alpha), prevents the compiler from refetching
  681.  * (and from merging fetches), and, more importantly, documents exactly
  682.  * which pointers are protected by RCU and checks that the pointer is
  683.  * annotated as __rcu.
  684.  */
  685. #define rcu_dereference_check(p, c) \
  686.         __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
  687.  
  688. /**
  689.  * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
  690.  * @p: The pointer to read, prior to dereferencing
  691.  * @c: The conditions under which the dereference will take place
  692.  *
  693.  * This is the RCU-bh counterpart to rcu_dereference_check().
  694.  */
  695. #define rcu_dereference_bh_check(p, c) \
  696.         __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
  697.  
  698. /**
  699.  * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
  700.  * @p: The pointer to read, prior to dereferencing
  701.  * @c: The conditions under which the dereference will take place
  702.  *
  703.  * This is the RCU-sched counterpart to rcu_dereference_check().
  704.  */
  705. #define rcu_dereference_sched_check(p, c) \
  706.         __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
  707.                                 __rcu)
  708.  
  709. #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
  710.  
  711. /*
  712.  * The tracing infrastructure traces RCU (we want that), but unfortunately
  713.  * some of the RCU checks causes tracing to lock up the system.
  714.  *
  715.  * The no-tracing version of rcu_dereference_raw() must not call
  716.  * rcu_read_lock_held().
  717.  */
  718. #define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu)
  719.  
  720. /**
  721.  * rcu_dereference_protected() - fetch RCU pointer when updates prevented
  722.  * @p: The pointer to read, prior to dereferencing
  723.  * @c: The conditions under which the dereference will take place
  724.  *
  725.  * Return the value of the specified RCU-protected pointer, but omit
  726.  * both the smp_read_barrier_depends() and the READ_ONCE().  This
  727.  * is useful in cases where update-side locks prevent the value of the
  728.  * pointer from changing.  Please note that this primitive does -not-
  729.  * prevent the compiler from repeating this reference or combining it
  730.  * with other references, so it should not be used without protection
  731.  * of appropriate locks.
  732.  *
  733.  * This function is only for update-side use.  Using this function
  734.  * when protected only by rcu_read_lock() will result in infrequent
  735.  * but very ugly failures.
  736.  */
  737. #define rcu_dereference_protected(p, c) \
  738.         __rcu_dereference_protected((p), (c), __rcu)
  739.  
  740.  
  741. /**
  742.  * rcu_dereference() - fetch RCU-protected pointer for dereferencing
  743.  * @p: The pointer to read, prior to dereferencing
  744.  *
  745.  * This is a simple wrapper around rcu_dereference_check().
  746.  */
  747. #define rcu_dereference(p) rcu_dereference_check(p, 0)
  748.  
  749. /**
  750.  * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
  751.  * @p: The pointer to read, prior to dereferencing
  752.  *
  753.  * Makes rcu_dereference_check() do the dirty work.
  754.  */
  755. #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
  756.  
  757. /**
  758.  * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
  759.  * @p: The pointer to read, prior to dereferencing
  760.  *
  761.  * Makes rcu_dereference_check() do the dirty work.
  762.  */
  763. #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
  764.  
  765. /**
  766.  * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
  767.  * @p: The pointer to hand off
  768.  *
  769.  * This is simply an identity function, but it documents where a pointer
  770.  * is handed off from RCU to some other synchronization mechanism, for
  771.  * example, reference counting or locking.  In C11, it would map to
  772.  * kill_dependency().  It could be used as follows:
  773.  *
  774.  *      rcu_read_lock();
  775.  *      p = rcu_dereference(gp);
  776.  *      long_lived = is_long_lived(p);
  777.  *      if (long_lived) {
  778.  *              if (!atomic_inc_not_zero(p->refcnt))
  779.  *                      long_lived = false;
  780.  *              else
  781.  *                      p = rcu_pointer_handoff(p);
  782.  *      }
  783.  *      rcu_read_unlock();
  784.  */
  785. #define rcu_pointer_handoff(p) (p)
  786.  
  787. /**
  788.  * rcu_read_lock() - mark the beginning of an RCU read-side critical section
  789.  *
  790.  * When synchronize_rcu() is invoked on one CPU while other CPUs
  791.  * are within RCU read-side critical sections, then the
  792.  * synchronize_rcu() is guaranteed to block until after all the other
  793.  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
  794.  * on one CPU while other CPUs are within RCU read-side critical
  795.  * sections, invocation of the corresponding RCU callback is deferred
  796.  * until after the all the other CPUs exit their critical sections.
  797.  *
  798.  * Note, however, that RCU callbacks are permitted to run concurrently
  799.  * with new RCU read-side critical sections.  One way that this can happen
  800.  * is via the following sequence of events: (1) CPU 0 enters an RCU
  801.  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
  802.  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
  803.  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
  804.  * callback is invoked.  This is legal, because the RCU read-side critical
  805.  * section that was running concurrently with the call_rcu() (and which
  806.  * therefore might be referencing something that the corresponding RCU
  807.  * callback would free up) has completed before the corresponding
  808.  * RCU callback is invoked.
  809.  *
  810.  * RCU read-side critical sections may be nested.  Any deferred actions
  811.  * will be deferred until the outermost RCU read-side critical section
  812.  * completes.
  813.  *
  814.  * You can avoid reading and understanding the next paragraph by
  815.  * following this rule: don't put anything in an rcu_read_lock() RCU
  816.  * read-side critical section that would block in a !PREEMPT kernel.
  817.  * But if you want the full story, read on!
  818.  *
  819.  * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
  820.  * it is illegal to block while in an RCU read-side critical section.
  821.  * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPT
  822.  * kernel builds, RCU read-side critical sections may be preempted,
  823.  * but explicit blocking is illegal.  Finally, in preemptible RCU
  824.  * implementations in real-time (with -rt patchset) kernel builds, RCU
  825.  * read-side critical sections may be preempted and they may also block, but
  826.  * only when acquiring spinlocks that are subject to priority inheritance.
  827.  */
  828. static inline void rcu_read_lock(void)
  829. {
  830.         __rcu_read_lock();
  831.         __acquire(RCU);
  832.         rcu_lock_acquire(&rcu_lock_map);
  833.         RCU_LOCKDEP_WARN(!rcu_is_watching(),
  834.                          "rcu_read_lock() used illegally while idle");
  835. }
  836.  
  837. /*
  838.  * So where is rcu_write_lock()?  It does not exist, as there is no
  839.  * way for writers to lock out RCU readers.  This is a feature, not
  840.  * a bug -- this property is what provides RCU's performance benefits.
  841.  * Of course, writers must coordinate with each other.  The normal
  842.  * spinlock primitives work well for this, but any other technique may be
  843.  * used as well.  RCU does not care how the writers keep out of each
  844.  * others' way, as long as they do so.
  845.  */
  846.  
  847. /**
  848.  * rcu_read_unlock() - marks the end of an RCU read-side critical section.
  849.  *
  850.  * In most situations, rcu_read_unlock() is immune from deadlock.
  851.  * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
  852.  * is responsible for deboosting, which it does via rt_mutex_unlock().
  853.  * Unfortunately, this function acquires the scheduler's runqueue and
  854.  * priority-inheritance spinlocks.  This means that deadlock could result
  855.  * if the caller of rcu_read_unlock() already holds one of these locks or
  856.  * any lock that is ever acquired while holding them; or any lock which
  857.  * can be taken from interrupt context because rcu_boost()->rt_mutex_lock()
  858.  * does not disable irqs while taking ->wait_lock.
  859.  *
  860.  * That said, RCU readers are never priority boosted unless they were
  861.  * preempted.  Therefore, one way to avoid deadlock is to make sure
  862.  * that preemption never happens within any RCU read-side critical
  863.  * section whose outermost rcu_read_unlock() is called with one of
  864.  * rt_mutex_unlock()'s locks held.  Such preemption can be avoided in
  865.  * a number of ways, for example, by invoking preempt_disable() before
  866.  * critical section's outermost rcu_read_lock().
  867.  *
  868.  * Given that the set of locks acquired by rt_mutex_unlock() might change
  869.  * at any time, a somewhat more future-proofed approach is to make sure
  870.  * that that preemption never happens within any RCU read-side critical
  871.  * section whose outermost rcu_read_unlock() is called with irqs disabled.
  872.  * This approach relies on the fact that rt_mutex_unlock() currently only
  873.  * acquires irq-disabled locks.
  874.  *
  875.  * The second of these two approaches is best in most situations,
  876.  * however, the first approach can also be useful, at least to those
  877.  * developers willing to keep abreast of the set of locks acquired by
  878.  * rt_mutex_unlock().
  879.  *
  880.  * See rcu_read_lock() for more information.
  881.  */
  882. static inline void rcu_read_unlock(void)
  883. {
  884.         RCU_LOCKDEP_WARN(!rcu_is_watching(),
  885.                          "rcu_read_unlock() used illegally while idle");
  886.         __release(RCU);
  887.         __rcu_read_unlock();
  888.         rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
  889. }
  890.  
  891. /**
  892.  * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
  893.  *
  894.  * This is equivalent of rcu_read_lock(), but to be used when updates
  895.  * are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
  896.  * both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
  897.  * softirq handler to be a quiescent state, a process in RCU read-side
  898.  * critical section must be protected by disabling softirqs. Read-side
  899.  * critical sections in interrupt context can use just rcu_read_lock(),
  900.  * though this should at least be commented to avoid confusing people
  901.  * reading the code.
  902.  *
  903.  * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
  904.  * must occur in the same context, for example, it is illegal to invoke
  905.  * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
  906.  * was invoked from some other task.
  907.  */
  908. static inline void rcu_read_lock_bh(void)
  909. {
  910.         local_bh_disable();
  911.         __acquire(RCU_BH);
  912.         rcu_lock_acquire(&rcu_bh_lock_map);
  913.         RCU_LOCKDEP_WARN(!rcu_is_watching(),
  914.                          "rcu_read_lock_bh() used illegally while idle");
  915. }
  916.  
  917. /*
  918.  * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
  919.  *
  920.  * See rcu_read_lock_bh() for more information.
  921.  */
  922. static inline void rcu_read_unlock_bh(void)
  923. {
  924.         RCU_LOCKDEP_WARN(!rcu_is_watching(),
  925.                          "rcu_read_unlock_bh() used illegally while idle");
  926.         rcu_lock_release(&rcu_bh_lock_map);
  927.         __release(RCU_BH);
  928.         local_bh_enable();
  929. }
  930.  
  931. /**
  932.  * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
  933.  *
  934.  * This is equivalent of rcu_read_lock(), but to be used when updates
  935.  * are being done using call_rcu_sched() or synchronize_rcu_sched().
  936.  * Read-side critical sections can also be introduced by anything that
  937.  * disables preemption, including local_irq_disable() and friends.
  938.  *
  939.  * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
  940.  * must occur in the same context, for example, it is illegal to invoke
  941.  * rcu_read_unlock_sched() from process context if the matching
  942.  * rcu_read_lock_sched() was invoked from an NMI handler.
  943.  */
  944. static inline void rcu_read_lock_sched(void)
  945. {
  946.         preempt_disable();
  947.         __acquire(RCU_SCHED);
  948.         rcu_lock_acquire(&rcu_sched_lock_map);
  949.         RCU_LOCKDEP_WARN(!rcu_is_watching(),
  950.                          "rcu_read_lock_sched() used illegally while idle");
  951. }
  952.  
  953. /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
  954. static inline notrace void rcu_read_lock_sched_notrace(void)
  955. {
  956.         preempt_disable_notrace();
  957.         __acquire(RCU_SCHED);
  958. }
  959.  
  960. /*
  961.  * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
  962.  *
  963.  * See rcu_read_lock_sched for more information.
  964.  */
  965. static inline void rcu_read_unlock_sched(void)
  966. {
  967.         RCU_LOCKDEP_WARN(!rcu_is_watching(),
  968.                          "rcu_read_unlock_sched() used illegally while idle");
  969.         rcu_lock_release(&rcu_sched_lock_map);
  970.         __release(RCU_SCHED);
  971.         preempt_enable();
  972. }
  973.  
  974. /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
  975. static inline notrace void rcu_read_unlock_sched_notrace(void)
  976. {
  977.         __release(RCU_SCHED);
  978.         preempt_enable_notrace();
  979. }
  980.  
  981. /**
  982.  * RCU_INIT_POINTER() - initialize an RCU protected pointer
  983.  *
  984.  * Initialize an RCU-protected pointer in special cases where readers
  985.  * do not need ordering constraints on the CPU or the compiler.  These
  986.  * special cases are:
  987.  *
  988.  * 1.   This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
  989.  * 2.   The caller has taken whatever steps are required to prevent
  990.  *      RCU readers from concurrently accessing this pointer -or-
  991.  * 3.   The referenced data structure has already been exposed to
  992.  *      readers either at compile time or via rcu_assign_pointer() -and-
  993.  *      a.      You have not made -any- reader-visible changes to
  994.  *              this structure since then -or-
  995.  *      b.      It is OK for readers accessing this structure from its
  996.  *              new location to see the old state of the structure.  (For
  997.  *              example, the changes were to statistical counters or to
  998.  *              other state where exact synchronization is not required.)
  999.  *
  1000.  * Failure to follow these rules governing use of RCU_INIT_POINTER() will
  1001.  * result in impossible-to-diagnose memory corruption.  As in the structures
  1002.  * will look OK in crash dumps, but any concurrent RCU readers might
  1003.  * see pre-initialized values of the referenced data structure.  So
  1004.  * please be very careful how you use RCU_INIT_POINTER()!!!
  1005.  *
  1006.  * If you are creating an RCU-protected linked structure that is accessed
  1007.  * by a single external-to-structure RCU-protected pointer, then you may
  1008.  * use RCU_INIT_POINTER() to initialize the internal RCU-protected
  1009.  * pointers, but you must use rcu_assign_pointer() to initialize the
  1010.  * external-to-structure pointer -after- you have completely initialized
  1011.  * the reader-accessible portions of the linked structure.
  1012.  *
  1013.  * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
  1014.  * ordering guarantees for either the CPU or the compiler.
  1015.  */
  1016. #define RCU_INIT_POINTER(p, v) \
  1017.         do { \
  1018.                 rcu_dereference_sparse(p, __rcu); \
  1019.                 WRITE_ONCE(p, RCU_INITIALIZER(v)); \
  1020.         } while (0)
  1021.  
  1022. /**
  1023.  * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
  1024.  *
  1025.  * GCC-style initialization for an RCU-protected pointer in a structure field.
  1026.  */
  1027. #define RCU_POINTER_INITIALIZER(p, v) \
  1028.                 .p = RCU_INITIALIZER(v)
  1029.  
  1030. /*
  1031.  * Does the specified offset indicate that the corresponding rcu_head
  1032.  * structure can be handled by kfree_rcu()?
  1033.  */
  1034. #define __is_kfree_rcu_offset(offset) ((offset) < 4096)
  1035.  
  1036. /*
  1037.  * Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
  1038.  */
  1039. #define __kfree_rcu(head, offset) \
  1040.         do { \
  1041.                 BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
  1042.                 kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
  1043.         } while (0)
  1044.  
  1045. /**
  1046.  * kfree_rcu() - kfree an object after a grace period.
  1047.  * @ptr:        pointer to kfree
  1048.  * @rcu_head:   the name of the struct rcu_head within the type of @ptr.
  1049.  *
  1050.  * Many rcu callbacks functions just call kfree() on the base structure.
  1051.  * These functions are trivial, but their size adds up, and furthermore
  1052.  * when they are used in a kernel module, that module must invoke the
  1053.  * high-latency rcu_barrier() function at module-unload time.
  1054.  *
  1055.  * The kfree_rcu() function handles this issue.  Rather than encoding a
  1056.  * function address in the embedded rcu_head structure, kfree_rcu() instead
  1057.  * encodes the offset of the rcu_head structure within the base structure.
  1058.  * Because the functions are not allowed in the low-order 4096 bytes of
  1059.  * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
  1060.  * If the offset is larger than 4095 bytes, a compile-time error will
  1061.  * be generated in __kfree_rcu().  If this error is triggered, you can
  1062.  * either fall back to use of call_rcu() or rearrange the structure to
  1063.  * position the rcu_head structure into the first 4096 bytes.
  1064.  *
  1065.  * Note that the allowable offset might decrease in the future, for example,
  1066.  * to allow something like kmem_cache_free_rcu().
  1067.  *
  1068.  * The BUILD_BUG_ON check must not involve any function calls, hence the
  1069.  * checks are done in macros here.
  1070.  */
  1071. #define kfree_rcu(ptr, rcu_head)                                        \
  1072.         __kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
  1073.  
  1074. #ifdef CONFIG_TINY_RCU
  1075. static inline int rcu_needs_cpu(u64 basemono, u64 *nextevt)
  1076. {
  1077.         *nextevt = KTIME_MAX;
  1078.         return 0;
  1079. }
  1080. #endif /* #ifdef CONFIG_TINY_RCU */
  1081.  
  1082. #if defined(CONFIG_RCU_NOCB_CPU_ALL)
  1083. static inline bool rcu_is_nocb_cpu(int cpu) { return true; }
  1084. #elif defined(CONFIG_RCU_NOCB_CPU)
  1085. bool rcu_is_nocb_cpu(int cpu);
  1086. #else
  1087. static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
  1088. #endif
  1089.  
  1090.  
  1091. /* Only for use by adaptive-ticks code. */
  1092. #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
  1093. bool rcu_sys_is_idle(void);
  1094. void rcu_sysidle_force_exit(void);
  1095. #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
  1096.  
  1097. static inline bool rcu_sys_is_idle(void)
  1098. {
  1099.         return false;
  1100. }
  1101.  
  1102. static inline void rcu_sysidle_force_exit(void)
  1103. {
  1104. }
  1105.  
  1106. #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
  1107.  
  1108.  
  1109. #endif /* __LINUX_RCUPDATE_H */
  1110.