LCOV - code coverage report
Current view: top level - include/linux - rcupdate.h (source / functions) Hit Total Coverage
Test: landlock.info Lines: 64 70 91.4 %
Date: 2021-04-22 12:43:58 Functions: 8 9 88.9 %

          Line data    Source code
       1             : /* SPDX-License-Identifier: GPL-2.0+ */
       2             : /*
       3             :  * Read-Copy Update mechanism for mutual exclusion
       4             :  *
       5             :  * Copyright IBM Corporation, 2001
       6             :  *
       7             :  * Author: Dipankar Sarma <dipankar@in.ibm.com>
       8             :  *
       9             :  * Based on the original work by Paul McKenney <paulmck@vnet.ibm.com>
      10             :  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
      11             :  * Papers:
      12             :  * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
      13             :  * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
      14             :  *
      15             :  * For detailed explanation of Read-Copy Update mechanism see -
      16             :  *              http://lse.sourceforge.net/locking/rcupdate.html
      17             :  *
      18             :  */
      19             : 
      20             : #ifndef __LINUX_RCUPDATE_H
      21             : #define __LINUX_RCUPDATE_H
      22             : 
      23             : #include <linux/types.h>
      24             : #include <linux/compiler.h>
      25             : #include <linux/atomic.h>
      26             : #include <linux/irqflags.h>
      27             : #include <linux/preempt.h>
      28             : #include <linux/bottom_half.h>
      29             : #include <linux/lockdep.h>
      30             : #include <asm/processor.h>
      31             : #include <linux/cpumask.h>
      32             : 
      33             : #define ULONG_CMP_GE(a, b)      (ULONG_MAX / 2 >= (a) - (b))
      34             : #define ULONG_CMP_LT(a, b)      (ULONG_MAX / 2 < (a) - (b))
      35             : #define ulong2long(a)           (*(long *)(&(a)))
      36             : #define USHORT_CMP_GE(a, b)     (USHRT_MAX / 2 >= (unsigned short)((a) - (b)))
      37             : #define USHORT_CMP_LT(a, b)     (USHRT_MAX / 2 < (unsigned short)((a) - (b)))
      38             : 
      39             : /* Exported common interfaces */
      40             : void call_rcu(struct rcu_head *head, rcu_callback_t func);
      41             : void rcu_barrier_tasks(void);
      42             : void rcu_barrier_tasks_rude(void);
      43             : void synchronize_rcu(void);
      44             : 
      45             : #ifdef CONFIG_PREEMPT_RCU
      46             : 
      47             : void __rcu_read_lock(void);
      48             : void __rcu_read_unlock(void);
      49             : 
      50             : /*
      51             :  * Defined as a macro as it is a very low level header included from
      52             :  * areas that don't even know about current.  This gives the rcu_read_lock()
      53             :  * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
      54             :  * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
      55             :  */
      56             : #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
      57             : 
      58             : #else /* #ifdef CONFIG_PREEMPT_RCU */
      59             : 
      60             : #ifdef CONFIG_TINY_RCU
      61             : #define rcu_read_unlock_strict() do { } while (0)
      62             : #else
      63             : void rcu_read_unlock_strict(void);
      64             : #endif
      65             : 
      66     1087909 : static inline void __rcu_read_lock(void)
      67             : {
      68     2176067 :         preempt_disable();
      69             : }
      70             : 
      71     1088587 : static inline void __rcu_read_unlock(void)
      72             : {
      73     1088631 :         preempt_enable();
      74     1088631 :         rcu_read_unlock_strict();
      75     1088428 : }
      76             : 
      77     3128469 : static inline int rcu_preempt_depth(void)
      78             : {
      79     3128469 :         return 0;
      80             : }
      81             : 
      82             : #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
      83             : 
      84             : /* Internal to kernel */
      85             : void rcu_init(void);
      86             : extern int rcu_scheduler_active __read_mostly;
      87             : void rcu_sched_clock_irq(int user);
      88             : void rcu_report_dead(unsigned int cpu);
      89             : void rcutree_migrate_callbacks(int cpu);
      90             : 
      91             : #ifdef CONFIG_TASKS_RCU_GENERIC
      92             : void rcu_init_tasks_generic(void);
      93             : #else
      94           1 : static inline void rcu_init_tasks_generic(void) { }
      95             : #endif
      96             : 
      97             : #ifdef CONFIG_RCU_STALL_COMMON
      98             : void rcu_sysrq_start(void);
      99             : void rcu_sysrq_end(void);
     100             : #else /* #ifdef CONFIG_RCU_STALL_COMMON */
     101             : static inline void rcu_sysrq_start(void) { }
     102             : static inline void rcu_sysrq_end(void) { }
     103             : #endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */
     104             : 
     105             : #ifdef CONFIG_NO_HZ_FULL
     106             : void rcu_user_enter(void);
     107             : void rcu_user_exit(void);
     108             : #else
     109             : static inline void rcu_user_enter(void) { }
     110             : static inline void rcu_user_exit(void) { }
     111             : #endif /* CONFIG_NO_HZ_FULL */
     112             : 
     113             : #ifdef CONFIG_RCU_NOCB_CPU
     114             : void rcu_init_nohz(void);
     115             : int rcu_nocb_cpu_offload(int cpu);
     116             : int rcu_nocb_cpu_deoffload(int cpu);
     117             : void rcu_nocb_flush_deferred_wakeup(void);
     118             : #else /* #ifdef CONFIG_RCU_NOCB_CPU */
     119             : static inline void rcu_init_nohz(void) { }
     120             : static inline int rcu_nocb_cpu_offload(int cpu) { return -EINVAL; }
     121             : static inline int rcu_nocb_cpu_deoffload(int cpu) { return 0; }
     122      512765 : static inline void rcu_nocb_flush_deferred_wakeup(void) { }
     123             : #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
     124             : 
     125             : /**
     126             :  * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
     127             :  * @a: Code that RCU needs to pay attention to.
     128             :  *
     129             :  * RCU read-side critical sections are forbidden in the inner idle loop,
     130             :  * that is, between the rcu_idle_enter() and the rcu_idle_exit() -- RCU
     131             :  * will happily ignore any such read-side critical sections.  However,
     132             :  * things like powertop need tracepoints in the inner idle loop.
     133             :  *
     134             :  * This macro provides the way out:  RCU_NONIDLE(do_something_with_RCU())
     135             :  * will tell RCU that it needs to pay attention, invoke its argument
     136             :  * (in this example, calling the do_something_with_RCU() function),
     137             :  * and then tell RCU to go back to ignoring this CPU.  It is permissible
     138             :  * to nest RCU_NONIDLE() wrappers, but not indefinitely (but the limit is
     139             :  * on the order of a million or so, even on 32-bit systems).  It is
     140             :  * not legal to block within RCU_NONIDLE(), nor is it permissible to
     141             :  * transfer control either into or out of RCU_NONIDLE()'s statement.
     142             :  */
     143             : #define RCU_NONIDLE(a) \
     144             :         do { \
     145             :                 rcu_irq_enter_irqson(); \
     146             :                 do { a; } while (0); \
     147             :                 rcu_irq_exit_irqson(); \
     148             :         } while (0)
     149             : 
     150             : /*
     151             :  * Note a quasi-voluntary context switch for RCU-tasks's benefit.
     152             :  * This is a macro rather than an inline function to avoid #include hell.
     153             :  */
     154             : #ifdef CONFIG_TASKS_RCU_GENERIC
     155             : 
     156             : # ifdef CONFIG_TASKS_RCU
     157             : # define rcu_tasks_classic_qs(t, preempt)                               \
     158             :         do {                                                            \
     159             :                 if (!(preempt) && READ_ONCE((t)->rcu_tasks_holdout)) \
     160             :                         WRITE_ONCE((t)->rcu_tasks_holdout, false);   \
     161             :         } while (0)
     162             : void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
     163             : void synchronize_rcu_tasks(void);
     164             : # else
     165             : # define rcu_tasks_classic_qs(t, preempt) do { } while (0)
     166             : # define call_rcu_tasks call_rcu
     167             : # define synchronize_rcu_tasks synchronize_rcu
     168             : # endif
     169             : 
     170             : # ifdef CONFIG_TASKS_RCU_TRACE
     171             : # define rcu_tasks_trace_qs(t)                                          \
     172             :         do {                                                            \
     173             :                 if (!likely(READ_ONCE((t)->trc_reader_checked)) &&   \
     174             :                     !unlikely(READ_ONCE((t)->trc_reader_nesting))) { \
     175             :                         smp_store_release(&(t)->trc_reader_checked, true); \
     176             :                         smp_mb(); /* Readers partitioned by store. */   \
     177             :                 }                                                       \
     178             :         } while (0)
     179             : # else
     180             : # define rcu_tasks_trace_qs(t) do { } while (0)
     181             : # endif
     182             : 
     183             : #define rcu_tasks_qs(t, preempt)                                        \
     184             : do {                                                                    \
     185             :         rcu_tasks_classic_qs((t), (preempt));                           \
     186             :         rcu_tasks_trace_qs((t));                                        \
     187             : } while (0)
     188             : 
     189             : # ifdef CONFIG_TASKS_RUDE_RCU
     190             : void call_rcu_tasks_rude(struct rcu_head *head, rcu_callback_t func);
     191             : void synchronize_rcu_tasks_rude(void);
     192             : # endif
     193             : 
     194             : #define rcu_note_voluntary_context_switch(t) rcu_tasks_qs(t, false)
     195             : void exit_tasks_rcu_start(void);
     196             : void exit_tasks_rcu_finish(void);
     197             : #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
     198             : #define rcu_tasks_qs(t, preempt) do { } while (0)
     199             : #define rcu_note_voluntary_context_switch(t) do { } while (0)
     200             : #define call_rcu_tasks call_rcu
     201             : #define synchronize_rcu_tasks synchronize_rcu
     202           0 : static inline void exit_tasks_rcu_start(void) { }
     203           0 : static inline void exit_tasks_rcu_finish(void) { }
     204             : #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
     205             : 
     206             : /**
     207             :  * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
     208             :  *
     209             :  * This macro resembles cond_resched(), except that it is defined to
     210             :  * report potential quiescent states to RCU-tasks even if the cond_resched()
     211             :  * machinery were to be shut off, as some advocate for PREEMPTION kernels.
     212             :  */
     213             : #define cond_resched_tasks_rcu_qs() \
     214             : do { \
     215             :         rcu_tasks_qs(current, false); \
     216             :         cond_resched(); \
     217             : } while (0)
     218             : 
     219             : /*
     220             :  * Infrastructure to implement the synchronize_() primitives in
     221             :  * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
     222             :  */
     223             : 
     224             : #if defined(CONFIG_TREE_RCU)
     225             : #include <linux/rcutree.h>
     226             : #elif defined(CONFIG_TINY_RCU)
     227             : #include <linux/rcutiny.h>
     228             : #else
     229             : #error "Unknown RCU implementation specified to kernel configuration"
     230             : #endif
     231             : 
     232             : /*
     233             :  * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls
     234             :  * are needed for dynamic initialization and destruction of rcu_head
     235             :  * on the stack, and init_rcu_head()/destroy_rcu_head() are needed for
     236             :  * dynamic initialization and destruction of statically allocated rcu_head
     237             :  * structures.  However, rcu_head structures allocated dynamically in the
     238             :  * heap don't need any initialization.
     239             :  */
     240             : #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
     241             : void init_rcu_head(struct rcu_head *head);
     242             : void destroy_rcu_head(struct rcu_head *head);
     243             : void init_rcu_head_on_stack(struct rcu_head *head);
     244             : void destroy_rcu_head_on_stack(struct rcu_head *head);
     245             : #else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
     246             : static inline void init_rcu_head(struct rcu_head *head) { }
     247             : static inline void destroy_rcu_head(struct rcu_head *head) { }
     248             : static inline void init_rcu_head_on_stack(struct rcu_head *head) { }
     249             : static inline void destroy_rcu_head_on_stack(struct rcu_head *head) { }
     250             : #endif  /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
     251             : 
     252             : #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
     253             : bool rcu_lockdep_current_cpu_online(void);
     254             : #else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
     255             : static inline bool rcu_lockdep_current_cpu_online(void) { return true; }
     256             : #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
     257             : 
     258             : extern struct lockdep_map rcu_lock_map;
     259             : extern struct lockdep_map rcu_bh_lock_map;
     260             : extern struct lockdep_map rcu_sched_lock_map;
     261             : extern struct lockdep_map rcu_callback_map;
     262             : 
     263             : #ifdef CONFIG_DEBUG_LOCK_ALLOC
     264             : 
     265     1769342 : static inline void rcu_lock_acquire(struct lockdep_map *map)
     266             : {
     267     1769342 :         lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
     268     1769967 : }
     269             : 
     270     1762681 : static inline void rcu_lock_release(struct lockdep_map *map)
     271             : {
     272     1738431 :         lock_release(map, _THIS_IP_);
     273         929 : }
     274             : 
     275             : int debug_lockdep_rcu_enabled(void);
     276             : int rcu_read_lock_held(void);
     277             : int rcu_read_lock_bh_held(void);
     278             : int rcu_read_lock_sched_held(void);
     279             : int rcu_read_lock_any_held(void);
     280             : 
     281             : #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
     282             : 
     283             : # define rcu_lock_acquire(a)            do { } while (0)
     284             : # define rcu_lock_release(a)            do { } while (0)
     285             : 
     286             : static inline int rcu_read_lock_held(void)
     287             : {
     288             :         return 1;
     289             : }
     290             : 
     291             : static inline int rcu_read_lock_bh_held(void)
     292             : {
     293             :         return 1;
     294             : }
     295             : 
     296             : static inline int rcu_read_lock_sched_held(void)
     297             : {
     298             :         return !preemptible();
     299             : }
     300             : 
     301             : static inline int rcu_read_lock_any_held(void)
     302             : {
     303             :         return !preemptible();
     304             : }
     305             : 
     306             : #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
     307             : 
     308             : #ifdef CONFIG_PROVE_RCU
     309             : 
     310             : /**
     311             :  * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
     312             :  * @c: condition to check
     313             :  * @s: informative message
     314             :  */
     315             : #define RCU_LOCKDEP_WARN(c, s)                                          \
     316             :         do {                                                            \
     317             :                 static bool __section(".data.unlikely") __warned;     \
     318             :                 if (debug_lockdep_rcu_enabled() && !__warned && (c)) {  \
     319             :                         __warned = true;                                \
     320             :                         lockdep_rcu_suspicious(__FILE__, __LINE__, s);  \
     321             :                 }                                                       \
     322             :         } while (0)
     323             : 
     324             : #if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
     325     3157897 : static inline void rcu_preempt_sleep_check(void)
     326             : {
     327     6316826 :         RCU_LOCKDEP_WARN(lock_is_held(&rcu_lock_map),
     328             :                          "Illegal context switch in RCU read-side critical section");
     329     3160376 : }
     330             : #else /* #ifdef CONFIG_PROVE_RCU */
     331             : static inline void rcu_preempt_sleep_check(void) { }
     332             : #endif /* #else #ifdef CONFIG_PROVE_RCU */
     333             : 
     334             : #define rcu_sleep_check()                                               \
     335             :         do {                                                            \
     336             :                 rcu_preempt_sleep_check();                              \
     337             :                 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map),    \
     338             :                                  "Illegal context switch in RCU-bh read-side critical section"); \
     339             :                 RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map), \
     340             :                                  "Illegal context switch in RCU-sched read-side critical section"); \
     341             :         } while (0)
     342             : 
     343             : #else /* #ifdef CONFIG_PROVE_RCU */
     344             : 
     345             : #define RCU_LOCKDEP_WARN(c, s) do { } while (0 && (c))
     346             : #define rcu_sleep_check() do { } while (0)
     347             : 
     348             : #endif /* #else #ifdef CONFIG_PROVE_RCU */
     349             : 
     350             : /*
     351             :  * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
     352             :  * and rcu_assign_pointer().  Some of these could be folded into their
     353             :  * callers, but they are left separate in order to ease introduction of
     354             :  * multiple pointers markings to match different RCU implementations
     355             :  * (e.g., __srcu), should this make sense in the future.
     356             :  */
     357             : 
     358             : #ifdef __CHECKER__
     359             : #define rcu_check_sparse(p, space) \
     360             :         ((void)(((typeof(*p) space *)p) == p))
     361             : #else /* #ifdef __CHECKER__ */
     362             : #define rcu_check_sparse(p, space)
     363             : #endif /* #else #ifdef __CHECKER__ */
     364             : 
     365             : #define __rcu_access_pointer(p, space) \
     366             : ({ \
     367             :         typeof(*p) *_________p1 = (typeof(*p) *__force)READ_ONCE(p); \
     368             :         rcu_check_sparse(p, space); \
     369             :         ((typeof(*p) __force __kernel *)(_________p1)); \
     370             : })
     371             : #define __rcu_dereference_check(p, c, space) \
     372             : ({ \
     373             :         /* Dependency order vs. p above. */ \
     374             :         typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
     375             :         RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
     376             :         rcu_check_sparse(p, space); \
     377             :         ((typeof(*p) __force __kernel *)(________p1)); \
     378             : })
     379             : #define __rcu_dereference_protected(p, c, space) \
     380             : ({ \
     381             :         RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_protected() usage"); \
     382             :         rcu_check_sparse(p, space); \
     383             :         ((typeof(*p) __force __kernel *)(p)); \
     384             : })
     385             : #define rcu_dereference_raw(p) \
     386             : ({ \
     387             :         /* Dependency order vs. p above. */ \
     388             :         typeof(p) ________p1 = READ_ONCE(p); \
     389             :         ((typeof(*p) __force __kernel *)(________p1)); \
     390             : })
     391             : 
     392             : /**
     393             :  * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
     394             :  * @v: The value to statically initialize with.
     395             :  */
     396             : #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
     397             : 
     398             : /**
     399             :  * rcu_assign_pointer() - assign to RCU-protected pointer
     400             :  * @p: pointer to assign to
     401             :  * @v: value to assign (publish)
     402             :  *
     403             :  * Assigns the specified value to the specified RCU-protected
     404             :  * pointer, ensuring that any concurrent RCU readers will see
     405             :  * any prior initialization.
     406             :  *
     407             :  * Inserts memory barriers on architectures that require them
     408             :  * (which is most of them), and also prevents the compiler from
     409             :  * reordering the code that initializes the structure after the pointer
     410             :  * assignment.  More importantly, this call documents which pointers
     411             :  * will be dereferenced by RCU read-side code.
     412             :  *
     413             :  * In some special cases, you may use RCU_INIT_POINTER() instead
     414             :  * of rcu_assign_pointer().  RCU_INIT_POINTER() is a bit faster due
     415             :  * to the fact that it does not constrain either the CPU or the compiler.
     416             :  * That said, using RCU_INIT_POINTER() when you should have used
     417             :  * rcu_assign_pointer() is a very bad thing that results in
     418             :  * impossible-to-diagnose memory corruption.  So please be careful.
     419             :  * See the RCU_INIT_POINTER() comment header for details.
     420             :  *
     421             :  * Note that rcu_assign_pointer() evaluates each of its arguments only
     422             :  * once, appearances notwithstanding.  One of the "extra" evaluations
     423             :  * is in typeof() and the other visible only to sparse (__CHECKER__),
     424             :  * neither of which actually execute the argument.  As with most cpp
     425             :  * macros, this execute-arguments-only-once property is important, so
     426             :  * please be careful when making changes to rcu_assign_pointer() and the
     427             :  * other macros that it invokes.
     428             :  */
     429             : #define rcu_assign_pointer(p, v)                                              \
     430             : do {                                                                          \
     431             :         uintptr_t _r_a_p__v = (uintptr_t)(v);                                 \
     432             :         rcu_check_sparse(p, __rcu);                                           \
     433             :                                                                               \
     434             :         if (__builtin_constant_p(v) && (_r_a_p__v) == (uintptr_t)NULL)        \
     435             :                 WRITE_ONCE((p), (typeof(p))(_r_a_p__v));                      \
     436             :         else                                                                  \
     437             :                 smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \
     438             : } while (0)
     439             : 
     440             : /**
     441             :  * rcu_replace_pointer() - replace an RCU pointer, returning its old value
     442             :  * @rcu_ptr: RCU pointer, whose old value is returned
     443             :  * @ptr: regular pointer
     444             :  * @c: the lockdep conditions under which the dereference will take place
     445             :  *
     446             :  * Perform a replacement, where @rcu_ptr is an RCU-annotated
     447             :  * pointer and @c is the lockdep argument that is passed to the
     448             :  * rcu_dereference_protected() call used to read that pointer.  The old
     449             :  * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr.
     450             :  */
     451             : #define rcu_replace_pointer(rcu_ptr, ptr, c)                            \
     452             : ({                                                                      \
     453             :         typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c));  \
     454             :         rcu_assign_pointer((rcu_ptr), (ptr));                           \
     455             :         __tmp;                                                          \
     456             : })
     457             : 
     458             : /**
     459             :  * rcu_access_pointer() - fetch RCU pointer with no dereferencing
     460             :  * @p: The pointer to read
     461             :  *
     462             :  * Return the value of the specified RCU-protected pointer, but omit the
     463             :  * lockdep checks for being in an RCU read-side critical section.  This is
     464             :  * useful when the value of this pointer is accessed, but the pointer is
     465             :  * not dereferenced, for example, when testing an RCU-protected pointer
     466             :  * against NULL.  Although rcu_access_pointer() may also be used in cases
     467             :  * where update-side locks prevent the value of the pointer from changing,
     468             :  * you should instead use rcu_dereference_protected() for this use case.
     469             :  *
     470             :  * It is also permissible to use rcu_access_pointer() when read-side
     471             :  * access to the pointer was removed at least one grace period ago, as
     472             :  * is the case in the context of the RCU callback that is freeing up
     473             :  * the data, or after a synchronize_rcu() returns.  This can be useful
     474             :  * when tearing down multi-linked structures after a grace period
     475             :  * has elapsed.
     476             :  */
     477             : #define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
     478             : 
     479             : /**
     480             :  * rcu_dereference_check() - rcu_dereference with debug checking
     481             :  * @p: The pointer to read, prior to dereferencing
     482             :  * @c: The conditions under which the dereference will take place
     483             :  *
     484             :  * Do an rcu_dereference(), but check that the conditions under which the
     485             :  * dereference will take place are correct.  Typically the conditions
     486             :  * indicate the various locking conditions that should be held at that
     487             :  * point.  The check should return true if the conditions are satisfied.
     488             :  * An implicit check for being in an RCU read-side critical section
     489             :  * (rcu_read_lock()) is included.
     490             :  *
     491             :  * For example:
     492             :  *
     493             :  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
     494             :  *
     495             :  * could be used to indicate to lockdep that foo->bar may only be dereferenced
     496             :  * if either rcu_read_lock() is held, or that the lock required to replace
     497             :  * the bar struct at foo->bar is held.
     498             :  *
     499             :  * Note that the list of conditions may also include indications of when a lock
     500             :  * need not be held, for example during initialisation or destruction of the
     501             :  * target struct:
     502             :  *
     503             :  *      bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
     504             :  *                                            atomic_read(&foo->usage) == 0);
     505             :  *
     506             :  * Inserts memory barriers on architectures that require them
     507             :  * (currently only the Alpha), prevents the compiler from refetching
     508             :  * (and from merging fetches), and, more importantly, documents exactly
     509             :  * which pointers are protected by RCU and checks that the pointer is
     510             :  * annotated as __rcu.
     511             :  */
     512             : #define rcu_dereference_check(p, c) \
     513             :         __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
     514             : 
     515             : /**
     516             :  * rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
     517             :  * @p: The pointer to read, prior to dereferencing
     518             :  * @c: The conditions under which the dereference will take place
     519             :  *
     520             :  * This is the RCU-bh counterpart to rcu_dereference_check().
     521             :  */
     522             : #define rcu_dereference_bh_check(p, c) \
     523             :         __rcu_dereference_check((p), (c) || rcu_read_lock_bh_held(), __rcu)
     524             : 
     525             : /**
     526             :  * rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
     527             :  * @p: The pointer to read, prior to dereferencing
     528             :  * @c: The conditions under which the dereference will take place
     529             :  *
     530             :  * This is the RCU-sched counterpart to rcu_dereference_check().
     531             :  */
     532             : #define rcu_dereference_sched_check(p, c) \
     533             :         __rcu_dereference_check((p), (c) || rcu_read_lock_sched_held(), \
     534             :                                 __rcu)
     535             : 
     536             : /*
     537             :  * The tracing infrastructure traces RCU (we want that), but unfortunately
     538             :  * some of the RCU checks causes tracing to lock up the system.
     539             :  *
     540             :  * The no-tracing version of rcu_dereference_raw() must not call
     541             :  * rcu_read_lock_held().
     542             :  */
     543             : #define rcu_dereference_raw_check(p) __rcu_dereference_check((p), 1, __rcu)
     544             : 
     545             : /**
     546             :  * rcu_dereference_protected() - fetch RCU pointer when updates prevented
     547             :  * @p: The pointer to read, prior to dereferencing
     548             :  * @c: The conditions under which the dereference will take place
     549             :  *
     550             :  * Return the value of the specified RCU-protected pointer, but omit
     551             :  * the READ_ONCE().  This is useful in cases where update-side locks
     552             :  * prevent the value of the pointer from changing.  Please note that this
     553             :  * primitive does *not* prevent the compiler from repeating this reference
     554             :  * or combining it with other references, so it should not be used without
     555             :  * protection of appropriate locks.
     556             :  *
     557             :  * This function is only for update-side use.  Using this function
     558             :  * when protected only by rcu_read_lock() will result in infrequent
     559             :  * but very ugly failures.
     560             :  */
     561             : #define rcu_dereference_protected(p, c) \
     562             :         __rcu_dereference_protected((p), (c), __rcu)
     563             : 
     564             : 
     565             : /**
     566             :  * rcu_dereference() - fetch RCU-protected pointer for dereferencing
     567             :  * @p: The pointer to read, prior to dereferencing
     568             :  *
     569             :  * This is a simple wrapper around rcu_dereference_check().
     570             :  */
     571             : #define rcu_dereference(p) rcu_dereference_check(p, 0)
     572             : 
     573             : /**
     574             :  * rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
     575             :  * @p: The pointer to read, prior to dereferencing
     576             :  *
     577             :  * Makes rcu_dereference_check() do the dirty work.
     578             :  */
     579             : #define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
     580             : 
     581             : /**
     582             :  * rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
     583             :  * @p: The pointer to read, prior to dereferencing
     584             :  *
     585             :  * Makes rcu_dereference_check() do the dirty work.
     586             :  */
     587             : #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
     588             : 
     589             : /**
     590             :  * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
     591             :  * @p: The pointer to hand off
     592             :  *
     593             :  * This is simply an identity function, but it documents where a pointer
     594             :  * is handed off from RCU to some other synchronization mechanism, for
     595             :  * example, reference counting or locking.  In C11, it would map to
     596             :  * kill_dependency().  It could be used as follows::
     597             :  *
     598             :  *      rcu_read_lock();
     599             :  *      p = rcu_dereference(gp);
     600             :  *      long_lived = is_long_lived(p);
     601             :  *      if (long_lived) {
     602             :  *              if (!atomic_inc_not_zero(p->refcnt))
     603             :  *                      long_lived = false;
     604             :  *              else
     605             :  *                      p = rcu_pointer_handoff(p);
     606             :  *      }
     607             :  *      rcu_read_unlock();
     608             :  */
     609             : #define rcu_pointer_handoff(p) (p)
     610             : 
     611             : /**
     612             :  * rcu_read_lock() - mark the beginning of an RCU read-side critical section
     613             :  *
     614             :  * When synchronize_rcu() is invoked on one CPU while other CPUs
     615             :  * are within RCU read-side critical sections, then the
     616             :  * synchronize_rcu() is guaranteed to block until after all the other
     617             :  * CPUs exit their critical sections.  Similarly, if call_rcu() is invoked
     618             :  * on one CPU while other CPUs are within RCU read-side critical
     619             :  * sections, invocation of the corresponding RCU callback is deferred
     620             :  * until after the all the other CPUs exit their critical sections.
     621             :  *
     622             :  * Note, however, that RCU callbacks are permitted to run concurrently
     623             :  * with new RCU read-side critical sections.  One way that this can happen
     624             :  * is via the following sequence of events: (1) CPU 0 enters an RCU
     625             :  * read-side critical section, (2) CPU 1 invokes call_rcu() to register
     626             :  * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
     627             :  * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
     628             :  * callback is invoked.  This is legal, because the RCU read-side critical
     629             :  * section that was running concurrently with the call_rcu() (and which
     630             :  * therefore might be referencing something that the corresponding RCU
     631             :  * callback would free up) has completed before the corresponding
     632             :  * RCU callback is invoked.
     633             :  *
     634             :  * RCU read-side critical sections may be nested.  Any deferred actions
     635             :  * will be deferred until the outermost RCU read-side critical section
     636             :  * completes.
     637             :  *
     638             :  * You can avoid reading and understanding the next paragraph by
     639             :  * following this rule: don't put anything in an rcu_read_lock() RCU
     640             :  * read-side critical section that would block in a !PREEMPTION kernel.
     641             :  * But if you want the full story, read on!
     642             :  *
     643             :  * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),
     644             :  * it is illegal to block while in an RCU read-side critical section.
     645             :  * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
     646             :  * kernel builds, RCU read-side critical sections may be preempted,
     647             :  * but explicit blocking is illegal.  Finally, in preemptible RCU
     648             :  * implementations in real-time (with -rt patchset) kernel builds, RCU
     649             :  * read-side critical sections may be preempted and they may also block, but
     650             :  * only when acquiring spinlocks that are subject to priority inheritance.
     651             :  */
     652     1087909 : static __always_inline void rcu_read_lock(void)
     653             : {
     654     1087909 :         __rcu_read_lock();
     655     1088158 :         __acquire(RCU);
     656     1088158 :         rcu_lock_acquire(&rcu_lock_map);
     657     1088244 :         RCU_LOCKDEP_WARN(!rcu_is_watching(),
     658             :                          "rcu_read_lock() used illegally while idle");
     659           4 : }
     660             : 
     661             : /*
     662             :  * So where is rcu_write_lock()?  It does not exist, as there is no
     663             :  * way for writers to lock out RCU readers.  This is a feature, not
     664             :  * a bug -- this property is what provides RCU's performance benefits.
     665             :  * Of course, writers must coordinate with each other.  The normal
     666             :  * spinlock primitives work well for this, but any other technique may be
     667             :  * used as well.  RCU does not care how the writers keep out of each
     668             :  * others' way, as long as they do so.
     669             :  */
     670             : 
     671             : /**
     672             :  * rcu_read_unlock() - marks the end of an RCU read-side critical section.
     673             :  *
     674             :  * In most situations, rcu_read_unlock() is immune from deadlock.
     675             :  * However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()
     676             :  * is responsible for deboosting, which it does via rt_mutex_unlock().
     677             :  * Unfortunately, this function acquires the scheduler's runqueue and
     678             :  * priority-inheritance spinlocks.  This means that deadlock could result
     679             :  * if the caller of rcu_read_unlock() already holds one of these locks or
     680             :  * any lock that is ever acquired while holding them.
     681             :  *
     682             :  * That said, RCU readers are never priority boosted unless they were
     683             :  * preempted.  Therefore, one way to avoid deadlock is to make sure
     684             :  * that preemption never happens within any RCU read-side critical
     685             :  * section whose outermost rcu_read_unlock() is called with one of
     686             :  * rt_mutex_unlock()'s locks held.  Such preemption can be avoided in
     687             :  * a number of ways, for example, by invoking preempt_disable() before
     688             :  * critical section's outermost rcu_read_lock().
     689             :  *
     690             :  * Given that the set of locks acquired by rt_mutex_unlock() might change
     691             :  * at any time, a somewhat more future-proofed approach is to make sure
     692             :  * that that preemption never happens within any RCU read-side critical
     693             :  * section whose outermost rcu_read_unlock() is called with irqs disabled.
     694             :  * This approach relies on the fact that rt_mutex_unlock() currently only
     695             :  * acquires irq-disabled locks.
     696             :  *
     697             :  * The second of these two approaches is best in most situations,
     698             :  * however, the first approach can also be useful, at least to those
     699             :  * developers willing to keep abreast of the set of locks acquired by
     700             :  * rt_mutex_unlock().
     701             :  *
     702             :  * See rcu_read_lock() for more information.
     703             :  */
     704     1088478 : static inline void rcu_read_unlock(void)
     705             : {
     706     1088478 :         RCU_LOCKDEP_WARN(!rcu_is_watching(),
     707             :                          "rcu_read_unlock() used illegally while idle");
     708     1088587 :         __release(RCU);
     709     1088587 :         __rcu_read_unlock();
     710     1088460 :         rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
     711     1088254 : }
     712             : 
     713             : /**
     714             :  * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
     715             :  *
     716             :  * This is equivalent of rcu_read_lock(), but also disables softirqs.
     717             :  * Note that anything else that disables softirqs can also serve as
     718             :  * an RCU read-side critical section.
     719             :  *
     720             :  * Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
     721             :  * must occur in the same context, for example, it is illegal to invoke
     722             :  * rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
     723             :  * was invoked from some other task.
     724             :  */
     725         897 : static inline void rcu_read_lock_bh(void)
     726             : {
     727         897 :         local_bh_disable();
     728         897 :         __acquire(RCU_BH);
     729         897 :         rcu_lock_acquire(&rcu_bh_lock_map);
     730         897 :         RCU_LOCKDEP_WARN(!rcu_is_watching(),
     731             :                          "rcu_read_lock_bh() used illegally while idle");
     732         897 : }
     733             : 
     734             : /**
     735             :  * rcu_read_unlock_bh() - marks the end of a softirq-only RCU critical section
     736             :  *
     737             :  * See rcu_read_lock_bh() for more information.
     738             :  */
     739         897 : static inline void rcu_read_unlock_bh(void)
     740             : {
     741         897 :         RCU_LOCKDEP_WARN(!rcu_is_watching(),
     742             :                          "rcu_read_unlock_bh() used illegally while idle");
     743         897 :         rcu_lock_release(&rcu_bh_lock_map);
     744         897 :         __release(RCU_BH);
     745         897 :         local_bh_enable();
     746         897 : }
     747             : 
     748             : /**
     749             :  * rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
     750             :  *
     751             :  * This is equivalent of rcu_read_lock(), but disables preemption.
     752             :  * Read-side critical sections can also be introduced by anything else
     753             :  * that disables preemption, including local_irq_disable() and friends.
     754             :  *
     755             :  * Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
     756             :  * must occur in the same context, for example, it is illegal to invoke
     757             :  * rcu_read_unlock_sched() from process context if the matching
     758             :  * rcu_read_lock_sched() was invoked from an NMI handler.
     759             :  */
     760       46442 : static inline void rcu_read_lock_sched(void)
     761             : {
     762       46442 :         preempt_disable();
     763       46445 :         __acquire(RCU_SCHED);
     764       46445 :         rcu_lock_acquire(&rcu_sched_lock_map);
     765       46444 :         RCU_LOCKDEP_WARN(!rcu_is_watching(),
     766             :                          "rcu_read_lock_sched() used illegally while idle");
     767       46452 : }
     768             : 
     769             : /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
     770    32815884 : static inline notrace void rcu_read_lock_sched_notrace(void)
     771             : {
     772    32815884 :         preempt_disable_notrace();
     773    32821220 :         __acquire(RCU_SCHED);
     774             : }
     775             : 
     776             : /**
     777             :  * rcu_read_unlock_sched() - marks the end of a RCU-classic critical section
     778             :  *
     779             :  * See rcu_read_lock_sched() for more information.
     780             :  */
     781       46444 : static inline void rcu_read_unlock_sched(void)
     782             : {
     783       46444 :         RCU_LOCKDEP_WARN(!rcu_is_watching(),
     784             :                          "rcu_read_unlock_sched() used illegally while idle");
     785       46446 :         rcu_lock_release(&rcu_sched_lock_map);
     786       46441 :         __release(RCU_SCHED);
     787       46441 :         preempt_enable();
     788       46441 : }
     789             : 
     790             : /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
     791    32811999 : static inline notrace void rcu_read_unlock_sched_notrace(void)
     792             : {
     793    32811999 :         __release(RCU_SCHED);
     794    32811999 :         preempt_enable_notrace();
     795    32835935 : }
     796             : 
     797             : /**
     798             :  * RCU_INIT_POINTER() - initialize an RCU protected pointer
     799             :  * @p: The pointer to be initialized.
     800             :  * @v: The value to initialized the pointer to.
     801             :  *
     802             :  * Initialize an RCU-protected pointer in special cases where readers
     803             :  * do not need ordering constraints on the CPU or the compiler.  These
     804             :  * special cases are:
     805             :  *
     806             :  * 1.   This use of RCU_INIT_POINTER() is NULLing out the pointer *or*
     807             :  * 2.   The caller has taken whatever steps are required to prevent
     808             :  *      RCU readers from concurrently accessing this pointer *or*
     809             :  * 3.   The referenced data structure has already been exposed to
     810             :  *      readers either at compile time or via rcu_assign_pointer() *and*
     811             :  *
     812             :  *      a.      You have not made *any* reader-visible changes to
     813             :  *              this structure since then *or*
     814             :  *      b.      It is OK for readers accessing this structure from its
     815             :  *              new location to see the old state of the structure.  (For
     816             :  *              example, the changes were to statistical counters or to
     817             :  *              other state where exact synchronization is not required.)
     818             :  *
     819             :  * Failure to follow these rules governing use of RCU_INIT_POINTER() will
     820             :  * result in impossible-to-diagnose memory corruption.  As in the structures
     821             :  * will look OK in crash dumps, but any concurrent RCU readers might
     822             :  * see pre-initialized values of the referenced data structure.  So
     823             :  * please be very careful how you use RCU_INIT_POINTER()!!!
     824             :  *
     825             :  * If you are creating an RCU-protected linked structure that is accessed
     826             :  * by a single external-to-structure RCU-protected pointer, then you may
     827             :  * use RCU_INIT_POINTER() to initialize the internal RCU-protected
     828             :  * pointers, but you must use rcu_assign_pointer() to initialize the
     829             :  * external-to-structure pointer *after* you have completely initialized
     830             :  * the reader-accessible portions of the linked structure.
     831             :  *
     832             :  * Note that unlike rcu_assign_pointer(), RCU_INIT_POINTER() provides no
     833             :  * ordering guarantees for either the CPU or the compiler.
     834             :  */
     835             : #define RCU_INIT_POINTER(p, v) \
     836             :         do { \
     837             :                 rcu_check_sparse(p, __rcu); \
     838             :                 WRITE_ONCE(p, RCU_INITIALIZER(v)); \
     839             :         } while (0)
     840             : 
     841             : /**
     842             :  * RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
     843             :  * @p: The pointer to be initialized.
     844             :  * @v: The value to initialized the pointer to.
     845             :  *
     846             :  * GCC-style initialization for an RCU-protected pointer in a structure field.
     847             :  */
     848             : #define RCU_POINTER_INITIALIZER(p, v) \
     849             :                 .p = RCU_INITIALIZER(v)
     850             : 
     851             : /*
     852             :  * Does the specified offset indicate that the corresponding rcu_head
     853             :  * structure can be handled by kvfree_rcu()?
     854             :  */
     855             : #define __is_kvfree_rcu_offset(offset) ((offset) < 4096)
     856             : 
     857             : /**
     858             :  * kfree_rcu() - kfree an object after a grace period.
     859             :  * @ptr: pointer to kfree for both single- and double-argument invocations.
     860             :  * @rhf: the name of the struct rcu_head within the type of @ptr,
     861             :  *       but only for double-argument invocations.
     862             :  *
     863             :  * Many rcu callbacks functions just call kfree() on the base structure.
     864             :  * These functions are trivial, but their size adds up, and furthermore
     865             :  * when they are used in a kernel module, that module must invoke the
     866             :  * high-latency rcu_barrier() function at module-unload time.
     867             :  *
     868             :  * The kfree_rcu() function handles this issue.  Rather than encoding a
     869             :  * function address in the embedded rcu_head structure, kfree_rcu() instead
     870             :  * encodes the offset of the rcu_head structure within the base structure.
     871             :  * Because the functions are not allowed in the low-order 4096 bytes of
     872             :  * kernel virtual memory, offsets up to 4095 bytes can be accommodated.
     873             :  * If the offset is larger than 4095 bytes, a compile-time error will
     874             :  * be generated in kvfree_rcu_arg_2(). If this error is triggered, you can
     875             :  * either fall back to use of call_rcu() or rearrange the structure to
     876             :  * position the rcu_head structure into the first 4096 bytes.
     877             :  *
     878             :  * Note that the allowable offset might decrease in the future, for example,
     879             :  * to allow something like kmem_cache_free_rcu().
     880             :  *
     881             :  * The BUILD_BUG_ON check must not involve any function calls, hence the
     882             :  * checks are done in macros here.
     883             :  */
     884             : #define kfree_rcu kvfree_rcu
     885             : 
     886             : /**
     887             :  * kvfree_rcu() - kvfree an object after a grace period.
     888             :  *
     889             :  * This macro consists of one or two arguments and it is
     890             :  * based on whether an object is head-less or not. If it
     891             :  * has a head then a semantic stays the same as it used
     892             :  * to be before:
     893             :  *
     894             :  *     kvfree_rcu(ptr, rhf);
     895             :  *
     896             :  * where @ptr is a pointer to kvfree(), @rhf is the name
     897             :  * of the rcu_head structure within the type of @ptr.
     898             :  *
     899             :  * When it comes to head-less variant, only one argument
     900             :  * is passed and that is just a pointer which has to be
     901             :  * freed after a grace period. Therefore the semantic is
     902             :  *
     903             :  *     kvfree_rcu(ptr);
     904             :  *
     905             :  * where @ptr is a pointer to kvfree().
     906             :  *
     907             :  * Please note, head-less way of freeing is permitted to
     908             :  * use from a context that has to follow might_sleep()
     909             :  * annotation. Otherwise, please switch and embed the
     910             :  * rcu_head structure within the type of @ptr.
     911             :  */
     912             : #define kvfree_rcu(...) KVFREE_GET_MACRO(__VA_ARGS__,           \
     913             :         kvfree_rcu_arg_2, kvfree_rcu_arg_1)(__VA_ARGS__)
     914             : 
     915             : #define KVFREE_GET_MACRO(_1, _2, NAME, ...) NAME
     916             : #define kvfree_rcu_arg_2(ptr, rhf)                                      \
     917             : do {                                                                    \
     918             :         typeof (ptr) ___p = (ptr);                                      \
     919             :                                                                         \
     920             :         if (___p) {                                                                     \
     921             :                 BUILD_BUG_ON(!__is_kvfree_rcu_offset(offsetof(typeof(*(ptr)), rhf)));   \
     922             :                 kvfree_call_rcu(&((___p)->rhf), (rcu_callback_t)(unsigned long)          \
     923             :                         (offsetof(typeof(*(ptr)), rhf)));                               \
     924             :         }                                                                               \
     925             : } while (0)
     926             : 
     927             : #define kvfree_rcu_arg_1(ptr)                                   \
     928             : do {                                                            \
     929             :         typeof(ptr) ___p = (ptr);                               \
     930             :                                                                 \
     931             :         if (___p)                                               \
     932             :                 kvfree_call_rcu(NULL, (rcu_callback_t) (___p)); \
     933             : } while (0)
     934             : 
     935             : /*
     936             :  * Place this after a lock-acquisition primitive to guarantee that
     937             :  * an UNLOCK+LOCK pair acts as a full barrier.  This guarantee applies
     938             :  * if the UNLOCK and LOCK are executed by the same CPU or if the
     939             :  * UNLOCK and LOCK operate on the same lock variable.
     940             :  */
     941             : #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE
     942             : #define smp_mb__after_unlock_lock()     smp_mb()  /* Full ordering for lock. */
     943             : #else /* #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
     944             : #define smp_mb__after_unlock_lock()     do { } while (0)
     945             : #endif /* #else #ifdef CONFIG_ARCH_WEAK_RELEASE_ACQUIRE */
     946             : 
     947             : 
     948             : /* Has the specified rcu_head structure been handed to call_rcu()? */
     949             : 
     950             : /**
     951             :  * rcu_head_init - Initialize rcu_head for rcu_head_after_call_rcu()
     952             :  * @rhp: The rcu_head structure to initialize.
     953             :  *
     954             :  * If you intend to invoke rcu_head_after_call_rcu() to test whether a
     955             :  * given rcu_head structure has already been passed to call_rcu(), then
     956             :  * you must also invoke this rcu_head_init() function on it just after
     957             :  * allocating that structure.  Calls to this function must not race with
     958             :  * calls to call_rcu(), rcu_head_after_call_rcu(), or callback invocation.
     959             :  */
     960          39 : static inline void rcu_head_init(struct rcu_head *rhp)
     961             : {
     962          39 :         rhp->func = (rcu_callback_t)~0L;
     963             : }
     964             : 
     965             : /**
     966             :  * rcu_head_after_call_rcu() - Has this rcu_head been passed to call_rcu()?
     967             :  * @rhp: The rcu_head structure to test.
     968             :  * @f: The function passed to call_rcu() along with @rhp.
     969             :  *
     970             :  * Returns @true if the @rhp has been passed to call_rcu() with @func,
     971             :  * and @false otherwise.  Emits a warning in any other case, including
     972             :  * the case where @rhp has already been invoked after a grace period.
     973             :  * Calls to this function must not race with callback invocation.  One way
     974             :  * to avoid such races is to enclose the call to rcu_head_after_call_rcu()
     975             :  * in an RCU read-side critical section that includes a read-side fetch
     976             :  * of the pointer to the structure containing @rhp.
     977             :  */
     978             : static inline bool
     979           0 : rcu_head_after_call_rcu(struct rcu_head *rhp, rcu_callback_t f)
     980             : {
     981           0 :         rcu_callback_t func = READ_ONCE(rhp->func);
     982             : 
     983           0 :         if (func == f)
     984             :                 return true;
     985           0 :         WARN_ON_ONCE(func != (rcu_callback_t)~0L);
     986             :         return false;
     987             : }
     988             : 
     989             : /* kernel/ksysfs.c definitions */
     990             : extern int rcu_expedited;
     991             : extern int rcu_normal;
     992             : 
     993             : #endif /* __LINUX_RCUPDATE_H */

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