[PATCH v4 03/25] notifier: Add atomic/blocking_notifier_has_unique_priority()

[Dmitry Osipenko <digetx@xxxxxxxxx>]

Add atomic/blocking_notifier_has_unique_priority() helpers which return
true if given handler has unique priority.

Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
---
 include/linux/notifier.h |  5 +++
 kernel/notifier.c        | 69 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+)

diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 924c9d7c8e73..2c4036f225e1 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -175,6 +175,11 @@ int raw_notifier_call_chain_robust(struct 
raw_notifier_head *nh,
 
 bool blocking_notifier_call_chain_is_empty(struct blocking_notifier_head *nh);
 
+bool atomic_notifier_has_unique_priority(struct atomic_notifier_head *nh,
+               struct notifier_block *nb);
+bool blocking_notifier_has_unique_priority(struct blocking_notifier_head *nh,
+               struct notifier_block *nb);
+
 #define NOTIFY_DONE            0x0000          /* Don't care */
 #define NOTIFY_OK              0x0001          /* Suits me */
 #define NOTIFY_STOP_MASK       0x8000          /* Don't call further */
diff --git a/kernel/notifier.c b/kernel/notifier.c
index b20cb7b9b1f0..7a325b742104 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -122,6 +122,19 @@ static int notifier_call_chain_robust(struct 
notifier_block **nl,
        return ret;
 }
 
+static int notifier_has_unique_priority(struct notifier_block **nl,
+                                       struct notifier_block *n)
+{
+       while (*nl && (*nl)->priority >= n->priority) {
+               if ((*nl)->priority == n->priority && *nl != n)
+                       return false;
+
+               nl = &((*nl)->next);
+       }
+
+       return true;
+}
+
 /*
  *     Atomic notifier chain routines.  Registration and unregistration
  *     use a spinlock, and call_chain is synchronized by RCU (no locks).
@@ -203,6 +216,30 @@ int atomic_notifier_call_chain(struct atomic_notifier_head 
*nh,
 EXPORT_SYMBOL_GPL(atomic_notifier_call_chain);
 NOKPROBE_SYMBOL(atomic_notifier_call_chain);
 
+/**
+ *     atomic_notifier_has_unique_priority - Checks whether notifier's 
priority is unique
+ *     @nh: Pointer to head of the atomic notifier chain
+ *     @n: Entry in notifier chain to check
+ *
+ *     Checks whether there is another notifier in the chain with the same 
priority.
+ *     Must be called in process context.
+ *
+ *     Returns true if priority is unique, false otherwise.
+ */
+bool atomic_notifier_has_unique_priority(struct atomic_notifier_head *nh,
+               struct notifier_block *n)
+{
+       unsigned long flags;
+       bool ret;
+
+       spin_lock_irqsave(&nh->lock, flags);
+       ret = notifier_has_unique_priority(&nh->head, n);
+       spin_unlock_irqrestore(&nh->lock, flags);
+
+       return ret;
+}
+EXPORT_SYMBOL_GPL(atomic_notifier_has_unique_priority);
+
 /*
  *     Blocking notifier chain routines.  All access to the chain is
  *     synchronized by an rwsem.
@@ -336,6 +373,38 @@ bool blocking_notifier_call_chain_is_empty(struct 
blocking_notifier_head *nh)
 }
 EXPORT_SYMBOL_GPL(blocking_notifier_call_chain_is_empty);
 
+/**
+ *     blocking_notifier_has_unique_priority - Checks whether notifier's 
priority is unique
+ *     @nh: Pointer to head of the blocking notifier chain
+ *     @n: Entry in notifier chain to check
+ *
+ *     Checks whether there is another notifier in the chain with the same 
priority.
+ *     Must be called in process context.
+ *
+ *     Returns true if priority is unique, false otherwise.
+ */
+bool blocking_notifier_has_unique_priority(struct blocking_notifier_head *nh,
+               struct notifier_block *n)
+{
+       bool 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_read().
+        */
+       if (system_state != SYSTEM_BOOTING)
+               down_read(&nh->rwsem);
+
+       ret = notifier_has_unique_priority(&nh->head, n);
+
+       if (system_state != SYSTEM_BOOTING)
+               up_read(&nh->rwsem);
+
+       return ret;
+}
+EXPORT_SYMBOL_GPL(blocking_notifier_has_unique_priority);
+
 /*
  *     Raw notifier chain routines.  There is no protection;
  *     the caller must provide it.  Use at your own risk!
-- 
2.33.1