FreeBSD/Linux Kernel Cross Reference
sys/kernel/notifier.c

     #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)
    {
            while ((*nl) != NULL) {
                    if (n->priority > (*nl)->priority)
                            break;
                    nl = &((*nl)->next);
            }
            n->next = *nl;
            rcu_assign_pointer(*nl, n);
            return 0;
    }
    
    static int notifier_chain_cond_register(struct notifier_block **nl,
                    struct notifier_block *n)
    {
            while ((*nl) != NULL) {
                    if ((*nl) == n)
                            return 0;
                    if (n->priority > (*nl)->priority)
                            break;
                    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.
     *      @returns:       notifier_call_chain returns the value returned by the
     *                      last notifier function called.
     */
    static int __kprobes 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) == NOTIFY_STOP_MASK)
                            break;
                   nb = next_nb;
                   nr_to_call--;
           }
           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.
    *
    *      Currently always returns zero.
    */
   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);
           spin_unlock_irqrestore(&nh->lock, flags);
           return ret;
   }
   EXPORT_SYMBOL_GPL(atomic_notifier_chain_register);
   
   /**
    *      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
    *      @nr_to_call: See the comment for notifier_call_chain.
    *      @nr_calls: See the comment for notifier_call_chain.
    *
    *      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 __kprobes __atomic_notifier_call_chain(struct atomic_notifier_head *nh,
                                           unsigned long val, void *v,
                                           int nr_to_call, int *nr_calls)
   {
           int ret;
   
           rcu_read_lock();
           ret = notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls);
           rcu_read_unlock();
           return ret;
   }
   EXPORT_SYMBOL_GPL(__atomic_notifier_call_chain);
   
   int __kprobes atomic_notifier_call_chain(struct atomic_notifier_head *nh,
                   unsigned long val, void *v)
   {
           return __atomic_notifier_call_chain(nh, val, v, -1, NULL);
   }
   EXPORT_SYMBOL_GPL(atomic_notifier_call_chain);
   
   /*
    *      Blocking notifier chain routines.  All access to the chain is
    *      synchronized by an rwsem.
    */
   
   /**
    *      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.
    *
    *      Currently always returns zero.
    */
   int blocking_notifier_chain_register(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_register(&nh->head, n);
   
           down_write(&nh->rwsem);
           ret = notifier_chain_register(&nh->head, n);
           up_write(&nh->rwsem);
           return ret;
   }
   EXPORT_SYMBOL_GPL(blocking_notifier_chain_register);
   
   /**
    *      blocking_notifier_chain_cond_register - Cond 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, only if not already
    *      present in the chain.
    *      Must be called in process context.
    *
    *      Currently always returns zero.
    */
   int blocking_notifier_chain_cond_register(struct blocking_notifier_head *nh,
                   struct notifier_block *n)
   {
           int ret;
   
           down_write(&nh->rwsem);
           ret = notifier_chain_cond_register(&nh->head, n);
           up_write(&nh->rwsem);
           return ret;
   }
   EXPORT_SYMBOL_GPL(blocking_notifier_chain_cond_register);
   
   /**
    *      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);
   
   /**
    *      __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
    *      @nr_to_call: See comment for notifier_call_chain.
    *      @nr_calls: See comment for notifier_call_chain.
    *
    *      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 nr_to_call, int *nr_calls)
   {
           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_dereference_raw(nh->head)) {
                   down_read(&nh->rwsem);
                   ret = notifier_call_chain(&nh->head, val, v, nr_to_call,
                                           nr_calls);
                   up_read(&nh->rwsem);
           }
           return ret;
   }
   EXPORT_SYMBOL_GPL(__blocking_notifier_call_chain);
   
   int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
                   unsigned long val, void *v)
   {
           return __blocking_notifier_call_chain(nh, val, v, -1, NULL);
   }
   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.
    *
    *      Currently always returns zero.
    */
   int raw_notifier_chain_register(struct raw_notifier_head *nh,
                   struct notifier_block *n)
   {
           return notifier_chain_register(&nh->head, n);
   }
   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);
   
   /**
    *      __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
    *      @nr_to_call: See comment for notifier_call_chain.
    *      @nr_calls: See comment for notifier_call_chain
    *
    *      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,
                                 int nr_to_call, int *nr_calls)
   {
           return notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls);
   }
   EXPORT_SYMBOL_GPL(__raw_notifier_call_chain);
   
   int raw_notifier_call_chain(struct raw_notifier_head *nh,
                   unsigned long val, void *v)
   {
           return __raw_notifier_call_chain(nh, 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.
    *
    *      Currently always returns zero.
    */
   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);
   
           mutex_lock(&nh->mutex);
           ret = notifier_chain_register(&nh->head, n);
           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
    *      @nr_to_call: See comment for notifier_call_chain.
    *      @nr_calls: See comment for notifier_call_chain
    *
    *      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 nr_to_call, int *nr_calls)
   {
           int ret;
           int idx;
   
           idx = srcu_read_lock(&nh->srcu);
           ret = notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls);
           srcu_read_unlock(&nh->srcu, idx);
           return ret;
   }
   EXPORT_SYMBOL_GPL(__srcu_notifier_call_chain);
   
   int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
                   unsigned long val, void *v)
   {
           return __srcu_notifier_call_chain(nh, val, v, -1, NULL);
   }
   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 __kprobes 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,
   
           };
           return atomic_notifier_call_chain(&die_chain, val, &args);
   }
   
   int register_die_notifier(struct notifier_block *nb)
   {
           vmalloc_sync_all();
           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);

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