ipc: re-enable msgmni automatic recomputing msgmni if set to negative

The enhancement as asked for by Yasunori: if msgmni is set to a negative
value, register it back into the ipcns notifier chain.

A new interface has been added to the notification mechanism:
notifier_chain_cond_register() registers a notifier block only if not already
registered.  With that new interface we avoid taking care of the states
changes in procfs.

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Cc: Yasunori Goto <y-goto@jp.fujitsu.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Mingming Cao <cmm@us.ibm.com>
Cc: Pierre Peiffer <pierre.peiffer@bull.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 38 insertions, 0 deletions

diff --git a/kernel/notifier.c b/kernel/notifier.c
index 643360d1bb14..823be11584ef 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -31,6 +31,21 @@ static int notifier_chain_register(struct notifier_block **nl,
         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)
 {
@@ -205,6 +220,29 @@ int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
 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