[PATCH 8/8] Re-enable msgmni automatic recomputing msgmni if set to negative

[Nadia . Derbey]

[PATCH 08/08]

This patch is 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@xxxxxxxx>

---
 include/linux/ipc_namespace.h |    1 
 include/linux/notifier.h      |    4 +++
 ipc/ipc_sysctl.c              |   45 ++++++++++++++++++++++++++++++++----------
 ipc/ipcns_notifier.c          |    9 ++++++++
 kernel/notifier.c             |   38 +++++++++++++++++++++++++++++++++++
 5 files changed, 87 insertions(+), 10 deletions(-)

Index: linux-2.6.24-mm1/ipc/ipc_sysctl.c
===================================================================
--- linux-2.6.24-mm1.orig/ipc/ipc_sysctl.c	2008-02-08 16:08:32.000000000 +0100
+++ linux-2.6.24-mm1/ipc/ipc_sysctl.c	2008-02-11 14:32:09.000000000 +0100
@@ -15,6 +15,8 @@
 #include <linux/sysctl.h>
 #include <linux/uaccess.h>
 #include <linux/ipc_namespace.h>
+#include <linux/msg.h>
+#include "util.h"
 
 static void *get_ipc(ctl_table *table)
 {
@@ -24,6 +26,27 @@ static void *get_ipc(ctl_table *table)
 	return which;
 }
 
+/*
+ * Routine that is called when a tunable has successfully been changed by
+ * hand and it has a callback routine registered on the ipc namespace notifier
+ * chain: we don't want such tunables to be recomputed anymore upon memory
+ * add/remove or ipc namespace creation/removal.
+ * They can come back to a recomputable state by being set to a <0 value.
+ */
+static void tunable_set_callback(int val)
+{
+	if (val >= 0)
+		unregister_ipcns_notifier(current->nsproxy->ipc_ns);
+	else {
+		/*
+		 * Re-enable automatic recomputing only if not already
+		 * enabled.
+		 */
+		recompute_msgmni(current->nsproxy->ipc_ns);
+		cond_register_ipcns_notifier(current->nsproxy->ipc_ns);
+	}
+}
+
 #ifdef CONFIG_PROC_FS
 static int proc_ipc_dointvec(ctl_table *table, int write, struct file *filp,
 	void __user *buffer, size_t *lenp, loff_t *ppos)
@@ -38,17 +61,17 @@ static int proc_ipc_dointvec(ctl_table *
 static int proc_ipc_callback_dointvec(ctl_table *table, int write,
 	struct file *filp, void __user *buffer, size_t *lenp, loff_t *ppos)
 {
+	struct ctl_table ipc_table;
 	size_t lenp_bef = *lenp;
 	int rc;
 
-	rc = proc_ipc_dointvec(table, write, filp, buffer, lenp, ppos);
+	memcpy(&ipc_table, table, sizeof(ipc_table));
+	ipc_table.data = get_ipc(table);
+
+	rc = proc_dointvec(&ipc_table, write, filp, buffer, lenp, ppos);
 
 	if (write && !rc && lenp_bef == *lenp)
-		/*
-		 * Tunable has successfully been changed from userland:
-		 * disable its automatic recomputing.
-		 */
-		unregister_ipcns_notifier(current->nsproxy->ipc_ns);
+		tunable_set_callback(*((int *)(ipc_table.data)));
 
 	return rc;
 }
@@ -119,12 +142,14 @@ static int sysctl_ipc_registered_data(ct
 	rc = sysctl_ipc_data(table, name, nlen, oldval, oldlenp, newval,
 		newlen);
 
-	if (newval && newlen && rc > 0)
+	if (newval && newlen && rc > 0) {
 		/*
-		 * Tunable has successfully been changed from userland:
-		 * disable its automatic recomputing.
+		 * Tunable has successfully been changed from userland
 		 */
-		unregister_ipcns_notifier(current->nsproxy->ipc_ns);
+		int *data = get_ipc(table);
+
+		tunable_set_callback(*data);
+	}
 
 	return rc;
 }
Index: linux-2.6.24-mm1/kernel/notifier.c
===================================================================
--- linux-2.6.24-mm1.orig/kernel/notifier.c	2008-02-07 13:40:46.000000000 +0100
+++ linux-2.6.24-mm1/kernel/notifier.c	2008-02-11 14:54:34.000000000 +0100
@@ -31,6 +31,21 @@ static int notifier_chain_register(struc
 	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(str
 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
Index: linux-2.6.24-mm1/include/linux/notifier.h
===================================================================
--- linux-2.6.24-mm1.orig/include/linux/notifier.h	2008-02-07 13:40:35.000000000 +0100
+++ linux-2.6.24-mm1/include/linux/notifier.h	2008-02-11 14:55:06.000000000 +0100
@@ -121,6 +121,10 @@ extern int raw_notifier_chain_register(s
 extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
 		struct notifier_block *nb);
 
+extern int blocking_notifier_chain_cond_register(
+		struct blocking_notifier_head *nh,
+		struct notifier_block *nb);
+
 extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
 		struct notifier_block *nb);
 extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
Index: linux-2.6.24-mm1/include/linux/ipc_namespace.h
===================================================================
--- linux-2.6.24-mm1.orig/include/linux/ipc_namespace.h	2008-02-08 14:35:08.000000000 +0100
+++ linux-2.6.24-mm1/include/linux/ipc_namespace.h	2008-02-11 11:19:31.000000000 +0100
@@ -52,6 +52,7 @@ extern atomic_t nr_ipc_ns;
 #define INIT_IPC_NS(ns)		.ns		= &init_ipc_ns,
 
 extern int register_ipcns_notifier(struct ipc_namespace *);
+extern int cond_register_ipcns_notifier(struct ipc_namespace *);
 extern int unregister_ipcns_notifier(struct ipc_namespace *);
 extern int ipcns_notify(unsigned long);
 
Index: linux-2.6.24-mm1/ipc/ipcns_notifier.c
===================================================================
--- linux-2.6.24-mm1.orig/ipc/ipcns_notifier.c	2008-02-08 14:36:05.000000000 +0100
+++ linux-2.6.24-mm1/ipc/ipcns_notifier.c	2008-02-11 12:24:39.000000000 +0100
@@ -61,6 +61,15 @@ int register_ipcns_notifier(struct ipc_n
 	return blocking_notifier_chain_register(&ipcns_chain, &ns->ipcns_nb);
 }
 
+int cond_register_ipcns_notifier(struct ipc_namespace *ns)
+{
+	memset(&ns->ipcns_nb, 0, sizeof(ns->ipcns_nb));
+	ns->ipcns_nb.notifier_call = ipcns_callback;
+	ns->ipcns_nb.priority = IPCNS_CALLBACK_PRI;
+	return blocking_notifier_chain_cond_register(&ipcns_chain,
+							&ns->ipcns_nb);
+}
+
 int unregister_ipcns_notifier(struct ipc_namespace *ns)
 {
 	return blocking_notifier_chain_unregister(&ipcns_chain,

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