linux/kernel/rcu/update.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * Read-Copy Update mechanism for mutual exclusion
 *
 * Copyright IBM Corporation, 2001
 *
 * Authors: Dipankar Sarma <[email protected]>
 *	    Manfred Spraul <[email protected]>
 *
 * Based on the original work by Paul McKenney <[email protected]>
 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
 * Papers:
 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
 *
 * For detailed explanation of Read-Copy Update mechanism see -
 *		http://lse.sourceforge.net/locking/rcupdate.html
 *
 */
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/interrupt.h>
#include <linux/sched/signal.h>
#include <linux/sched/debug.h>
#include <linux/torture.h>
#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/cpu.h>
#include <linux/mutex.h>
#include <linux/export.h>
#include <linux/hardirq.h>
#include <linux/delay.h>
#include <linux/moduleparam.h>
#include <linux/kthread.h>
#include <linux/tick.h>
#include <linux/rcupdate_wait.h>
#include <linux/sched/isolation.h>
#include <linux/kprobes.h>
#include <linux/slab.h>
#include <linux/irq_work.h>
#include <linux/rcupdate_trace.h>

#define CREATE_TRACE_POINTS

#include "rcu.h"

#ifdef MODULE_PARAM_PREFIX
#undef MODULE_PARAM_PREFIX
#endif
#define MODULE_PARAM_PREFIX …

#ifndef CONFIG_TINY_RCU
module_param(rcu_expedited, int, 0444);
module_param(rcu_normal, int, 0444);
static int rcu_normal_after_boot = … IS_ENABLED(…);
#if !defined(CONFIG_PREEMPT_RT) || defined(CONFIG_NO_HZ_FULL)
module_param(rcu_normal_after_boot, int, 0444);
#endif
#endif /* #ifndef CONFIG_TINY_RCU */

#ifdef CONFIG_DEBUG_LOCK_ALLOC
/**
 * rcu_read_lock_held_common() - might we be in RCU-sched read-side critical section?
 * @ret:	Best guess answer if lockdep cannot be relied on
 *
 * Returns true if lockdep must be ignored, in which case ``*ret`` contains
 * the best guess described below.  Otherwise returns false, in which
 * case ``*ret`` tells the caller nothing and the caller should instead
 * consult lockdep.
 *
 * If CONFIG_DEBUG_LOCK_ALLOC is selected, set ``*ret`` to nonzero iff in an
 * RCU-sched read-side critical section.  In absence of
 * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
 * critical section unless it can prove otherwise.  Note that disabling
 * of preemption (including disabling irqs) counts as an RCU-sched
 * read-side critical section.  This is useful for debug checks in functions
 * that required that they be called within an RCU-sched read-side
 * critical section.
 *
 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
 * and while lockdep is disabled.
 *
 * Note that if the CPU is in the idle loop from an RCU point of view (ie:
 * that we are in the section between ct_idle_enter() and ct_idle_exit())
 * then rcu_read_lock_held() sets ``*ret`` to false even if the CPU did an
 * rcu_read_lock().  The reason for this is that RCU ignores CPUs that are
 * in such a section, considering these as in extended quiescent state,
 * so such a CPU is effectively never in an RCU read-side critical section
 * regardless of what RCU primitives it invokes.  This state of affairs is
 * required --- we need to keep an RCU-free window in idle where the CPU may
 * possibly enter into low power mode. This way we can notice an extended
 * quiescent state to other CPUs that started a grace period. Otherwise
 * we would delay any grace period as long as we run in the idle task.
 *
 * Similarly, we avoid claiming an RCU read lock held if the current
 * CPU is offline.
 */
static bool rcu_read_lock_held_common(bool *ret)
{ … }

int rcu_read_lock_sched_held(void)
{ … }
EXPORT_SYMBOL(…);
#endif

#ifndef CONFIG_TINY_RCU

/*
 * Should expedited grace-period primitives always fall back to their
 * non-expedited counterparts?  Intended for use within RCU.  Note
 * that if the user specifies both rcu_expedited and rcu_normal, then
 * rcu_normal wins.  (Except during the time period during boot from
 * when the first task is spawned until the rcu_set_runtime_mode()
 * core_initcall() is invoked, at which point everything is expedited.)
 */
bool rcu_gp_is_normal(void)
{ … }
EXPORT_SYMBOL_GPL(…);

static atomic_t rcu_async_hurry_nesting = …;
/*
 * Should call_rcu() callbacks be processed with urgency or are
 * they OK being executed with arbitrary delays?
 */
bool rcu_async_should_hurry(void)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * rcu_async_hurry - Make future async RCU callbacks not lazy.
 *
 * After a call to this function, future calls to call_rcu()
 * will be processed in a timely fashion.
 */
void rcu_async_hurry(void)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * rcu_async_relax - Make future async RCU callbacks lazy.
 *
 * After a call to this function, future calls to call_rcu()
 * will be processed in a lazy fashion.
 */
void rcu_async_relax(void)
{ … }
EXPORT_SYMBOL_GPL(…);

static atomic_t rcu_expedited_nesting = …;
/*
 * Should normal grace-period primitives be expedited?  Intended for
 * use within RCU.  Note that this function takes the rcu_expedited
 * sysfs/boot variable and rcu_scheduler_active into account as well
 * as the rcu_expedite_gp() nesting.  So looping on rcu_unexpedite_gp()
 * until rcu_gp_is_expedited() returns false is a -really- bad idea.
 */
bool rcu_gp_is_expedited(void)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * rcu_expedite_gp - Expedite future RCU grace periods
 *
 * After a call to this function, future calls to synchronize_rcu() and
 * friends act as the corresponding synchronize_rcu_expedited() function
 * had instead been called.
 */
void rcu_expedite_gp(void)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * rcu_unexpedite_gp - Cancel prior rcu_expedite_gp() invocation
 *
 * Undo a prior call to rcu_expedite_gp().  If all prior calls to
 * rcu_expedite_gp() are undone by a subsequent call to rcu_unexpedite_gp(),
 * and if the rcu_expedited sysfs/boot parameter is not set, then all
 * subsequent calls to synchronize_rcu() and friends will return to
 * their normal non-expedited behavior.
 */
void rcu_unexpedite_gp(void)
{ … }
EXPORT_SYMBOL_GPL(…);

static bool rcu_boot_ended __read_mostly;

/*
 * Inform RCU of the end of the in-kernel boot sequence.
 */
void rcu_end_inkernel_boot(void)
{ … }

/*
 * Let rcutorture know when it is OK to turn it up to eleven.
 */
bool rcu_inkernel_boot_has_ended(void)
{ … }
EXPORT_SYMBOL_GPL(…);

#endif /* #ifndef CONFIG_TINY_RCU */

/*
 * Test each non-SRCU synchronous grace-period wait API.  This is
 * useful just after a change in mode for these primitives, and
 * during early boot.
 */
void rcu_test_sync_prims(void)
{ … }

#if !defined(CONFIG_TINY_RCU)

/*
 * Switch to run-time mode once RCU has fully initialized.
 */
static int __init rcu_set_runtime_mode(void)
{ … }
core_initcall(rcu_set_runtime_mode);

#endif /* #if !defined(CONFIG_TINY_RCU) */

#ifdef CONFIG_DEBUG_LOCK_ALLOC
static struct lock_class_key rcu_lock_key;
struct lockdep_map rcu_lock_map = …;
EXPORT_SYMBOL_GPL(…);

static struct lock_class_key rcu_bh_lock_key;
struct lockdep_map rcu_bh_lock_map = …;
EXPORT_SYMBOL_GPL(…);

static struct lock_class_key rcu_sched_lock_key;
struct lockdep_map rcu_sched_lock_map = …;
EXPORT_SYMBOL_GPL(…);

// Tell lockdep when RCU callbacks are being invoked.
static struct lock_class_key rcu_callback_key;
struct lockdep_map rcu_callback_map = …;
EXPORT_SYMBOL_GPL(…);

noinstr int notrace debug_lockdep_rcu_enabled(void)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * rcu_read_lock_held() - might we be in RCU read-side critical section?
 *
 * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
 * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
 * this assumes we are in an RCU read-side critical section unless it can
 * prove otherwise.  This is useful for debug checks in functions that
 * require that they be called within an RCU read-side critical section.
 *
 * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
 * and while lockdep is disabled.
 *
 * Note that rcu_read_lock() and the matching rcu_read_unlock() must
 * occur in the same context, for example, it is illegal to invoke
 * rcu_read_unlock() in process context if the matching rcu_read_lock()
 * was invoked from within an irq handler.
 *
 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
 * offline from an RCU perspective, so check for those as well.
 */
int rcu_read_lock_held(void)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
 *
 * Check for bottom half being disabled, which covers both the
 * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
 * will show the situation.  This is useful for debug checks in functions
 * that require that they be called within an RCU read-side critical
 * section.
 *
 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
 *
 * Note that rcu_read_lock_bh() is disallowed if the CPU is either idle or
 * offline from an RCU perspective, so check for those as well.
 */
int rcu_read_lock_bh_held(void)
{ … }
EXPORT_SYMBOL_GPL(…);

int rcu_read_lock_any_held(void)
{ … }
EXPORT_SYMBOL_GPL(…);

#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */

/**
 * wakeme_after_rcu() - Callback function to awaken a task after grace period
 * @head: Pointer to rcu_head member within rcu_synchronize structure
 *
 * Awaken the corresponding task now that a grace period has elapsed.
 */
void wakeme_after_rcu(struct rcu_head *head)
{ … }
EXPORT_SYMBOL_GPL(…);

void __wait_rcu_gp(bool checktiny, unsigned int state, int n, call_rcu_func_t *crcu_array,
		   struct rcu_synchronize *rs_array)
{ … }
EXPORT_SYMBOL_GPL(…);

void finish_rcuwait(struct rcuwait *w)
{ … }
EXPORT_SYMBOL_GPL(…);

#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
void init_rcu_head(struct rcu_head *head)
{ … }
EXPORT_SYMBOL_GPL(…);

void destroy_rcu_head(struct rcu_head *head)
{ … }
EXPORT_SYMBOL_GPL(…);

static bool rcuhead_is_static_object(void *addr)
{ … }

/**
 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 * @head: pointer to rcu_head structure to be initialized
 *
 * This function informs debugobjects of a new rcu_head structure that
 * has been allocated as an auto variable on the stack.  This function
 * is not required for rcu_head structures that are statically defined or
 * that are dynamically allocated on the heap.  This function has no
 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 */
void init_rcu_head_on_stack(struct rcu_head *head)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 * @head: pointer to rcu_head structure to be initialized
 *
 * This function informs debugobjects that an on-stack rcu_head structure
 * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 * function is not required for rcu_head structures that are statically
 * defined or that are dynamically allocated on the heap.  Also as with
 * init_rcu_head_on_stack(), this function has no effect for
 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 */
void destroy_rcu_head_on_stack(struct rcu_head *head)
{ … }
EXPORT_SYMBOL_GPL(…);

const struct debug_obj_descr rcuhead_debug_descr = …;
EXPORT_SYMBOL_GPL(…);
#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */

#if defined(CONFIG_TREE_RCU) || defined(CONFIG_RCU_TRACE)
void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
			       unsigned long secs,
			       unsigned long c_old, unsigned long c)
{ … }
EXPORT_SYMBOL_GPL(…);
#else
#define do_trace_rcu_torture_read …
#endif

#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST) || IS_ENABLED(CONFIG_LOCK_TORTURE_TEST) || IS_MODULE(CONFIG_LOCK_TORTURE_TEST)
/* Get rcutorture access to sched_setaffinity(). */
long torture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
{ … }
EXPORT_SYMBOL_GPL(…);
#endif

int rcu_cpu_stall_notifiers __read_mostly; // !0 = provide stall notifiers (rarely useful)
EXPORT_SYMBOL_GPL(…);

#ifdef CONFIG_RCU_STALL_COMMON
int rcu_cpu_stall_ftrace_dump __read_mostly;
module_param(rcu_cpu_stall_ftrace_dump, int, 0644);
#ifdef CONFIG_RCU_CPU_STALL_NOTIFIER
module_param(rcu_cpu_stall_notifiers, int, 0444);
#endif // #ifdef CONFIG_RCU_CPU_STALL_NOTIFIER
int rcu_cpu_stall_suppress __read_mostly; // !0 = suppress stall warnings.
EXPORT_SYMBOL_GPL(…);
module_param(rcu_cpu_stall_suppress, int, 0644);
int rcu_cpu_stall_timeout __read_mostly = …;
module_param(rcu_cpu_stall_timeout, int, 0644);
int rcu_exp_cpu_stall_timeout __read_mostly = …;
module_param(rcu_exp_cpu_stall_timeout, int, 0644);
int rcu_cpu_stall_cputime __read_mostly = … IS_ENABLED(…);
module_param(rcu_cpu_stall_cputime, int, 0644);
bool rcu_exp_stall_task_details __read_mostly;
module_param(rcu_exp_stall_task_details, bool, 0644);
#endif /* #ifdef CONFIG_RCU_STALL_COMMON */

// Suppress boot-time RCU CPU stall warnings and rcutorture writer stall
// warnings.  Also used by rcutorture even if stall warnings are excluded.
int rcu_cpu_stall_suppress_at_boot __read_mostly; // !0 = suppress boot stalls.
EXPORT_SYMBOL_GPL(…);
module_param(rcu_cpu_stall_suppress_at_boot, int, 0444);

/**
 * get_completed_synchronize_rcu - Return a pre-completed polled state cookie
 *
 * Returns a value that will always be treated by functions like
 * poll_state_synchronize_rcu() as a cookie whose grace period has already
 * completed.
 */
unsigned long get_completed_synchronize_rcu(void)
{ … }
EXPORT_SYMBOL_GPL(…);

#ifdef CONFIG_PROVE_RCU

/*
 * Early boot self test parameters.
 */
static bool rcu_self_test;
module_param(rcu_self_test, bool, 0444);

static int rcu_self_test_counter;

static void test_callback(struct rcu_head *r)
{ … }

DEFINE_STATIC_SRCU(…);
static unsigned long early_srcu_cookie;

struct early_boot_kfree_rcu { … };

static void early_boot_test_call_rcu(void)
{ … }

void rcu_early_boot_tests(void)
{ … }

static int rcu_verify_early_boot_tests(void)
{ … }
late_initcall(rcu_verify_early_boot_tests);
#else
void rcu_early_boot_tests(void) {}
#endif /* CONFIG_PROVE_RCU */

#include "tasks.h"

#ifndef CONFIG_TINY_RCU

/*
 * Print any significant non-default boot-time settings.
 */
void __init rcupdate_announce_bootup_oddness(void)
{ … }

#endif /* #ifndef CONFIG_TINY_RCU */