linux/kernel/notifier.c

// SPDX-License-Identifier: GPL-2.0-only
#include <linux/kdebug.h>
#include <linux/kprobes.h>
#include <linux/export.h>
#include <linux/notifier.h>
#include <linux/rcupdate.h>
#include <linux/vmalloc.h>
#include <linux/reboot.h>

/*
 *	Notifier list for kernel code which wants to be called
 *	at shutdown. This is used to stop any idling DMA operations
 *	and the like.
 */
BLOCKING_NOTIFIER_HEAD(reboot_notifier_list);

/*
 *	Notifier chain core routines.  The exported routines below
 *	are layered on top of these, with appropriate locking added.
 */

static int notifier_chain_register(struct notifier_block **nl,
				   struct notifier_block *n,
				   bool unique_priority)
{
	while ((*nl) != NULL) {
		if (unlikely((*nl) == n)) {
			WARN(1, "notifier callback %ps already registered",
			     n->notifier_call);
			return -EEXIST;
		}
		if (n->priority > (*nl)->priority)
			break;
		if (n->priority == (*nl)->priority && unique_priority)
			return -EBUSY;
		nl = &((*nl)->next);
	}
	n->next = *nl;
	rcu_assign_pointer(*nl, n);
	return 0;
}

static int notifier_chain_unregister(struct notifier_block **nl,
		struct notifier_block *n)
{
	while ((*nl) != NULL) {
		if ((*nl) == n) {
			rcu_assign_pointer(*nl, n->next);
			return 0;
		}
		nl = &((*nl)->next);
	}
	return -ENOENT;
}

/**
 * notifier_call_chain - Informs the registered notifiers about an event.
 *	@nl:		Pointer to head of the blocking notifier chain
 *	@val:		Value passed unmodified to notifier function
 *	@v:		Pointer passed unmodified to notifier function
 *	@nr_to_call:	Number of notifier functions to be called. Don't care
 *			value of this parameter is -1.
 *	@nr_calls:	Records the number of notifications sent. Don't care
 *			value of this field is NULL.
 *	Return:		notifier_call_chain returns the value returned by the
 *			last notifier function called.
 */
static int notifier_call_chain(struct notifier_block **nl,
			       unsigned long val, void *v,
			       int nr_to_call, int *nr_calls)
{
	int ret = NOTIFY_DONE;
	struct notifier_block *nb, *next_nb;

	nb = rcu_dereference_raw(*nl);

	while (nb && nr_to_call) {
		next_nb = rcu_dereference_raw(nb->next);

#ifdef CONFIG_DEBUG_NOTIFIERS
		if (unlikely(!func_ptr_is_kernel_text(nb->notifier_call))) {
			WARN(1, "Invalid notifier called!");
			nb = next_nb;
			continue;
		}
#endif
		ret = nb->notifier_call(nb, val, v);

		if (nr_calls)
			(*nr_calls)++;

		if (ret & NOTIFY_STOP_MASK)
			break;
		nb = next_nb;
		nr_to_call--;
	}
	return ret;
}
NOKPROBE_SYMBOL(notifier_call_chain);

/**
 * notifier_call_chain_robust - Inform the registered notifiers about an event
 *                              and rollback on error.
 * @nl:		Pointer to head of the blocking notifier chain
 * @val_up:	Value passed unmodified to the notifier function
 * @val_down:	Value passed unmodified to the notifier function when recovering
 *              from an error on @val_up
 * @v:		Pointer passed unmodified to the notifier function
 *
 * NOTE:	It is important the @nl chain doesn't change between the two
 *		invocations of notifier_call_chain() such that we visit the
 *		exact same notifier callbacks; this rules out any RCU usage.
 *
 * Return:	the return value of the @val_up call.
 */
static int notifier_call_chain_robust(struct notifier_block **nl,
				     unsigned long val_up, unsigned long val_down,
				     void *v)
{
	int ret, nr = 0;

	ret = notifier_call_chain(nl, val_up, v, -1, &nr);
	if (ret & NOTIFY_STOP_MASK)
		notifier_call_chain(nl, val_down, v, nr-1, NULL);

	return ret;
}

/*
 *	Atomic notifier chain routines.  Registration and unregistration
 *	use a spinlock, and call_chain is synchronized by RCU (no locks).
 */

/**
 *	atomic_notifier_chain_register - Add notifier to an atomic notifier chain
 *	@nh: Pointer to head of the atomic notifier chain
 *	@n: New entry in notifier chain
 *
 *	Adds a notifier to an atomic notifier chain.
 *
 *	Returns 0 on success, %-EEXIST on error.
 */
int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
		struct notifier_block *n)
{
	unsigned long flags;
	int ret;

	spin_lock_irqsave(&nh->lock, flags);
	ret = notifier_chain_register(&nh->head, n, false);
	spin_unlock_irqrestore(&nh->lock, flags);
	return ret;
}
EXPORT_SYMBOL_GPL(atomic_notifier_chain_register);

/**
 *	atomic_notifier_chain_register_unique_prio - Add notifier to an atomic notifier chain
 *	@nh: Pointer to head of the atomic notifier chain
 *	@n: New entry in notifier chain
 *
 *	Adds a notifier to an atomic notifier chain if there is no other
 *	notifier registered using the same priority.
 *
 *	Returns 0 on success, %-EEXIST or %-EBUSY on error.
 */
int atomic_notifier_chain_register_unique_prio(struct atomic_notifier_head *nh,
					       struct notifier_block *n)
{
	unsigned long flags;
	int ret;

	spin_lock_irqsave(&nh->lock, flags);
	ret = notifier_chain_register(&nh->head, n, true);
	spin_unlock_irqrestore(&nh->lock, flags);
	return ret;
}
EXPORT_SYMBOL_GPL(atomic_notifier_chain_register_unique_prio);

/**
 *	atomic_notifier_chain_unregister - Remove notifier from an atomic notifier chain
 *	@nh: Pointer to head of the atomic notifier chain
 *	@n: Entry to remove from notifier chain
 *
 *	Removes a notifier from an atomic notifier chain.
 *
 *	Returns zero on success or %-ENOENT on failure.
 */
int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
		struct notifier_block *n)
{
	unsigned long flags;
	int ret;

	spin_lock_irqsave(&nh->lock, flags);
	ret = notifier_chain_unregister(&nh->head, n);
	spin_unlock_irqrestore(&nh->lock, flags);
	synchronize_rcu();
	return ret;
}
EXPORT_SYMBOL_GPL(atomic_notifier_chain_unregister);

/**
 *	atomic_notifier_call_chain - Call functions in an atomic notifier chain
 *	@nh: Pointer to head of the atomic notifier chain
 *	@val: Value passed unmodified to notifier function
 *	@v: Pointer passed unmodified to notifier function
 *
 *	Calls each function in a notifier chain in turn.  The functions
 *	run in an atomic context, so they must not block.
 *	This routine uses RCU to synchronize with changes to the chain.
 *
 *	If the return value of the notifier can be and'ed
 *	with %NOTIFY_STOP_MASK then atomic_notifier_call_chain()
 *	will return immediately, with the return value of
 *	the notifier function which halted execution.
 *	Otherwise the return value is the return value
 *	of the last notifier function called.
 */
int atomic_notifier_call_chain(struct atomic_notifier_head *nh,
			       unsigned long val, void *v)
{
	int ret;

	rcu_read_lock();
	ret = notifier_call_chain(&nh->head, val, v, -1, NULL);
	rcu_read_unlock();

	return ret;
}
EXPORT_SYMBOL_GPL(atomic_notifier_call_chain);
NOKPROBE_SYMBOL(atomic_notifier_call_chain);

/**
 *	atomic_notifier_call_chain_is_empty - Check whether notifier chain is empty
 *	@nh: Pointer to head of the atomic notifier chain
 *
 *	Checks whether notifier chain is empty.
 *
 *	Returns true is notifier chain is empty, false otherwise.
 */
bool atomic_notifier_call_chain_is_empty(struct atomic_notifier_head *nh)
{
	return !rcu_access_pointer(nh->head);
}

/*
 *	Blocking notifier chain routines.  All access to the chain is
 *	synchronized by an rwsem.
 */

static int __blocking_notifier_chain_register(struct blocking_notifier_head *nh,
					      struct notifier_block *n,
					      bool unique_priority)
{
	int ret;

	/*
	 * This code gets used during boot-up, when task switching is
	 * not yet working and interrupts must remain disabled.  At
	 * such times we must not call down_write().
	 */
	if (unlikely(system_state == SYSTEM_BOOTING))
		return notifier_chain_register(&nh->head, n, unique_priority);

	down_write(&nh->rwsem);
	ret = notifier_chain_register(&nh->head, n, unique_priority);
	up_write(&nh->rwsem);
	return ret;
}

/**
 *	blocking_notifier_chain_register - Add notifier to a blocking notifier chain
 *	@nh: Pointer to head of the blocking notifier chain
 *	@n: New entry in notifier chain
 *
 *	Adds a notifier to a blocking notifier chain.
 *	Must be called in process context.
 *
 *	Returns 0 on success, %-EEXIST on error.
 */
int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
		struct notifier_block *n)
{
	return __blocking_notifier_chain_register(nh, n, false);
}
EXPORT_SYMBOL_GPL(blocking_notifier_chain_register);

/**
 *	blocking_notifier_chain_register_unique_prio - Add notifier to a blocking notifier chain
 *	@nh: Pointer to head of the blocking notifier chain
 *	@n: New entry in notifier chain
 *
 *	Adds a notifier to an blocking notifier chain if there is no other
 *	notifier registered using the same priority.
 *
 *	Returns 0 on success, %-EEXIST or %-EBUSY on error.
 */
int blocking_notifier_chain_register_unique_prio(struct blocking_notifier_head *nh,
						 struct notifier_block *n)
{
	return __blocking_notifier_chain_register(nh, n, true);
}
EXPORT_SYMBOL_GPL(blocking_notifier_chain_register_unique_prio);

/**
 *	blocking_notifier_chain_unregister - Remove notifier from a blocking notifier chain
 *	@nh: Pointer to head of the blocking notifier chain
 *	@n: Entry to remove from notifier chain
 *
 *	Removes a notifier from a blocking notifier chain.
 *	Must be called from process context.
 *
 *	Returns zero on success or %-ENOENT on failure.
 */
int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
		struct notifier_block *n)
{
	int ret;

	/*
	 * This code gets used during boot-up, when task switching is
	 * not yet working and interrupts must remain disabled.  At
	 * such times we must not call down_write().
	 */
	if (unlikely(system_state == SYSTEM_BOOTING))
		return notifier_chain_unregister(&nh->head, n);

	down_write(&nh->rwsem);
	ret = notifier_chain_unregister(&nh->head, n);
	up_write(&nh->rwsem);
	return ret;
}
EXPORT_SYMBOL_GPL(blocking_notifier_chain_unregister);

int blocking_notifier_call_chain_robust(struct blocking_notifier_head *nh,
		unsigned long val_up, unsigned long val_down, void *v)
{
	int ret = NOTIFY_DONE;

	/*
	 * We check the head outside the lock, but if this access is
	 * racy then it does not matter what the result of the test
	 * is, we re-check the list after having taken the lock anyway:
	 */
	if (rcu_access_pointer(nh->head)) {
		down_read(&nh->rwsem);
		ret = notifier_call_chain_robust(&nh->head, val_up, val_down, v);
		up_read(&nh->rwsem);
	}
	return ret;
}
EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_robust);

/**
 *	blocking_notifier_call_chain - Call functions in a blocking notifier chain
 *	@nh: Pointer to head of the blocking notifier chain
 *	@val: Value passed unmodified to notifier function
 *	@v: Pointer passed unmodified to notifier function
 *
 *	Calls each function in a notifier chain in turn.  The functions
 *	run in a process context, so they are allowed to block.
 *
 *	If the return value of the notifier can be and'ed
 *	with %NOTIFY_STOP_MASK then blocking_notifier_call_chain()
 *	will return immediately, with the return value of
 *	the notifier function which halted execution.
 *	Otherwise the return value is the return value
 *	of the last notifier function called.
 */
int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
		unsigned long val, void *v)
{
	int ret = NOTIFY_DONE;

	/*
	 * We check the head outside the lock, but if this access is
	 * racy then it does not matter what the result of the test
	 * is, we re-check the list after having taken the lock anyway:
	 */
	if (rcu_access_pointer(nh->head)) {
		down_read(&nh->rwsem);
		ret = notifier_call_chain(&nh->head, val, v, -1, NULL);
		up_read(&nh->rwsem);
	}
	return ret;
}
EXPORT_SYMBOL_GPL(blocking_notifier_call_chain);

/*
 *	Raw notifier chain routines.  There is no protection;
 *	the caller must provide it.  Use at your own risk!
 */

/**
 *	raw_notifier_chain_register - Add notifier to a raw notifier chain
 *	@nh: Pointer to head of the raw notifier chain
 *	@n: New entry in notifier chain
 *
 *	Adds a notifier to a raw notifier chain.
 *	All locking must be provided by the caller.
 *
 *	Returns 0 on success, %-EEXIST on error.
 */
int raw_notifier_chain_register(struct raw_notifier_head *nh,
		struct notifier_block *n)
{
	return notifier_chain_register(&nh->head, n, false);
}
EXPORT_SYMBOL_GPL(raw_notifier_chain_register);

/**
 *	raw_notifier_chain_unregister - Remove notifier from a raw notifier chain
 *	@nh: Pointer to head of the raw notifier chain
 *	@n: Entry to remove from notifier chain
 *
 *	Removes a notifier from a raw notifier chain.
 *	All locking must be provided by the caller.
 *
 *	Returns zero on success or %-ENOENT on failure.
 */
int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
		struct notifier_block *n)
{
	return notifier_chain_unregister(&nh->head, n);
}
EXPORT_SYMBOL_GPL(raw_notifier_chain_unregister);

int raw_notifier_call_chain_robust(struct raw_notifier_head *nh,
		unsigned long val_up, unsigned long val_down, void *v)
{
	return notifier_call_chain_robust(&nh->head, val_up, val_down, v);
}
EXPORT_SYMBOL_GPL(raw_notifier_call_chain_robust);

/**
 *	raw_notifier_call_chain - Call functions in a raw notifier chain
 *	@nh: Pointer to head of the raw notifier chain
 *	@val: Value passed unmodified to notifier function
 *	@v: Pointer passed unmodified to notifier function
 *
 *	Calls each function in a notifier chain in turn.  The functions
 *	run in an undefined context.
 *	All locking must be provided by the caller.
 *
 *	If the return value of the notifier can be and'ed
 *	with %NOTIFY_STOP_MASK then raw_notifier_call_chain()
 *	will return immediately, with the return value of
 *	the notifier function which halted execution.
 *	Otherwise the return value is the return value
 *	of the last notifier function called.
 */
int raw_notifier_call_chain(struct raw_notifier_head *nh,
		unsigned long val, void *v)
{
	return notifier_call_chain(&nh->head, val, v, -1, NULL);
}
EXPORT_SYMBOL_GPL(raw_notifier_call_chain);

/*
 *	SRCU notifier chain routines.    Registration and unregistration
 *	use a mutex, and call_chain is synchronized by SRCU (no locks).
 */

/**
 *	srcu_notifier_chain_register - Add notifier to an SRCU notifier chain
 *	@nh: Pointer to head of the SRCU notifier chain
 *	@n: New entry in notifier chain
 *
 *	Adds a notifier to an SRCU notifier chain.
 *	Must be called in process context.
 *
 *	Returns 0 on success, %-EEXIST on error.
 */
int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
		struct notifier_block *n)
{
	int ret;

	/*
	 * This code gets used during boot-up, when task switching is
	 * not yet working and interrupts must remain disabled.  At
	 * such times we must not call mutex_lock().
	 */
	if (unlikely(system_state == SYSTEM_BOOTING))
		return notifier_chain_register(&nh->head, n, false);

	mutex_lock(&nh->mutex);
	ret = notifier_chain_register(&nh->head, n, false);
	mutex_unlock(&nh->mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(srcu_notifier_chain_register);

/**
 *	srcu_notifier_chain_unregister - Remove notifier from an SRCU notifier chain
 *	@nh: Pointer to head of the SRCU notifier chain
 *	@n: Entry to remove from notifier chain
 *
 *	Removes a notifier from an SRCU notifier chain.
 *	Must be called from process context.
 *
 *	Returns zero on success or %-ENOENT on failure.
 */
int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
		struct notifier_block *n)
{
	int ret;

	/*
	 * This code gets used during boot-up, when task switching is
	 * not yet working and interrupts must remain disabled.  At
	 * such times we must not call mutex_lock().
	 */
	if (unlikely(system_state == SYSTEM_BOOTING))
		return notifier_chain_unregister(&nh->head, n);

	mutex_lock(&nh->mutex);
	ret = notifier_chain_unregister(&nh->head, n);
	mutex_unlock(&nh->mutex);
	synchronize_srcu(&nh->srcu);
	return ret;
}
EXPORT_SYMBOL_GPL(srcu_notifier_chain_unregister);

/**
 *	srcu_notifier_call_chain - Call functions in an SRCU notifier chain
 *	@nh: Pointer to head of the SRCU notifier chain
 *	@val: Value passed unmodified to notifier function
 *	@v: Pointer passed unmodified to notifier function
 *
 *	Calls each function in a notifier chain in turn.  The functions
 *	run in a process context, so they are allowed to block.
 *
 *	If the return value of the notifier can be and'ed
 *	with %NOTIFY_STOP_MASK then srcu_notifier_call_chain()
 *	will return immediately, with the return value of
 *	the notifier function which halted execution.
 *	Otherwise the return value is the return value
 *	of the last notifier function called.
 */
int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
		unsigned long val, void *v)
{
	int ret;
	int idx;

	idx = srcu_read_lock(&nh->srcu);
	ret = notifier_call_chain(&nh->head, val, v, -1, NULL);
	srcu_read_unlock(&nh->srcu, idx);
	return ret;
}
EXPORT_SYMBOL_GPL(srcu_notifier_call_chain);

/**
 *	srcu_init_notifier_head - Initialize an SRCU notifier head
 *	@nh: Pointer to head of the srcu notifier chain
 *
 *	Unlike other sorts of notifier heads, SRCU notifier heads require
 *	dynamic initialization.  Be sure to call this routine before
 *	calling any of the other SRCU notifier routines for this head.
 *
 *	If an SRCU notifier head is deallocated, it must first be cleaned
 *	up by calling srcu_cleanup_notifier_head().  Otherwise the head's
 *	per-cpu data (used by the SRCU mechanism) will leak.
 */
void srcu_init_notifier_head(struct srcu_notifier_head *nh)
{
	mutex_init(&nh->mutex);
	if (init_srcu_struct(&nh->srcu) < 0)
		BUG();
	nh->head = NULL;
}
EXPORT_SYMBOL_GPL(srcu_init_notifier_head);

static ATOMIC_NOTIFIER_HEAD(die_chain);

int notrace notify_die(enum die_val val, const char *str,
	       struct pt_regs *regs, long err, int trap, int sig)
{
	struct die_args args = {
		.regs	= regs,
		.str	= str,
		.err	= err,
		.trapnr	= trap,
		.signr	= sig,

	};
	RCU_LOCKDEP_WARN(!rcu_is_watching(),
			   "notify_die called but RCU thinks we're quiescent");
	return atomic_notifier_call_chain(&die_chain, val, &args);
}
NOKPROBE_SYMBOL(notify_die);

int register_die_notifier(struct notifier_block *nb)
{
	return atomic_notifier_chain_register(&die_chain, nb);
}
EXPORT_SYMBOL_GPL(register_die_notifier);

int unregister_die_notifier(struct notifier_block *nb)
{
	return atomic_notifier_chain_unregister(&die_chain, nb);
}
EXPORT_SYMBOL_GPL(unregister_die_notifier);