1 files changed, 123 insertions, 1 deletions

diff --git a/kernel/sys.c b/kernel/sys.c
index 2314867ae34f..fd5c71006775 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -153,7 +153,7 @@ static int __kprobes notifier_call_chain(struct notifier_block **nl,
 
 /*
  *      Atomic notifier chain routines.  Registration and unregistration
- *      use a mutex, and call_chain is synchronized by RCU (no locks).
+ *      use a spinlock, and call_chain is synchronized by RCU (no locks).
  */
 
 /**
@@ -401,6 +401,128 @@ int raw_notifier_call_chain(struct raw_notifier_head *nh,
 
 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
+ *
+ *      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);
+        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);
+        init_srcu_struct(&nh->srcu);
+        nh->head = NULL;
+}
+
+EXPORT_SYMBOL_GPL(srcu_init_notifier_head);
+
 /**
  *      register_reboot_notifier - Register function to be called at reboot time
  *      @nb: Info about notifier function to be called