drm/modes: Fix drm_mode_vrefres() docs

[drm/drm-misc.git] / 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>

#define CREATE_TRACE_POINTS
#include <trace/events/notifier.h>

/*
 *      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);
        trace_notifier_register((void *)n->notifier_call);
        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);
                        trace_notifier_unregister((void *)n->notifier_call);
                        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
                trace_notifier_run((void *)nb->notifier_call);
                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);