6 files changed, 120 insertions, 2 deletions

diff --git a/ipc/Makefile b/ipc/Makefile
index 5fc5e33ea047..388e4d259f02 100644
--- a/ipc/Makefile
+++ b/ipc/Makefile
@@ -3,7 +3,8 @@
 #
 
 obj-$(CONFIG_SYSVIPC_COMPAT) += compat.o
-obj-$(CONFIG_SYSVIPC) += util.o msgutil.o msg.o sem.o shm.o
+obj_mem-$(CONFIG_MEMORY_HOTPLUG) += ipcns_notifier.o
+obj-$(CONFIG_SYSVIPC) += util.o msgutil.o msg.o sem.o shm.o $(obj_mem-y)
 obj-$(CONFIG_SYSVIPC_SYSCTL) += ipc_sysctl.o
 obj_mq-$(CONFIG_COMPAT) += compat_mq.o
 obj-$(CONFIG_POSIX_MQUEUE) += mqueue.o msgutil.o $(obj_mq-y)
diff --git a/ipc/ipcns_notifier.c b/ipc/ipcns_notifier.c
new file mode 100644
index 000000000000..0786af6ce3ec
--- /dev/null
+++ b/ipc/ipcns_notifier.c
@@ -0,0 +1,71 @@
+/*
+ * linux/ipc/ipcns_notifier.c
+ * Copyright (C) 2007 BULL SA. Nadia Derbey
+ *
+ * Notification mechanism for ipc namespaces:
+ * The callback routine registered in the memory chain invokes the ipcns
+ * notifier chain with the IPCNS_MEMCHANGED event.
+ * Each callback routine registered in the ipcns namespace recomputes msgmni
+ * for the owning namespace.
+ */
+
+#include <linux/msg.h>
+#include <linux/rcupdate.h>
+#include <linux/notifier.h>
+#include <linux/nsproxy.h>
+#include <linux/ipc_namespace.h>
+
+#include "util.h"
+
+
+
+static BLOCKING_NOTIFIER_HEAD(ipcns_chain);
+
+
+static int ipcns_callback(struct notifier_block *self,
+                                unsigned long action, void *arg)
+{
+        struct ipc_namespace *ns;
+
+        switch (action) {
+        case IPCNS_MEMCHANGED:   /* amount of lowmem has changed */
+                /*
+                 * It's time to recompute msgmni
+                 */
+                ns = container_of(self, struct ipc_namespace, ipcns_nb);
+                /*
+                 * No need to get a reference on the ns: the 1st job of
+                 * free_ipc_ns() is to unregister the callback routine.
+                 * blocking_notifier_chain_unregister takes the wr lock to do
+                 * it.
+                 * When this callback routine is called the rd lock is held by
+                 * blocking_notifier_call_chain.
+                 * So the ipc ns cannot be freed while we are here.
+                 */
+                recompute_msgmni(ns);
+                break;
+        default:
+                break;
+        }
+
+        return NOTIFY_OK;
+}
+
+int 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_register(&ipcns_chain, &ns->ipcns_nb);
+}
+
+int unregister_ipcns_notifier(struct ipc_namespace *ns)
+{
+        return blocking_notifier_chain_unregister(&ipcns_chain,
+                                                &ns->ipcns_nb);
+}
+
+int ipcns_notify(unsigned long val)
+{
+        return blocking_notifier_call_chain(&ipcns_chain, val, NULL);
+}
diff --git a/ipc/msg.c b/ipc/msg.c
index be8449d48a8e..7d9b0694c743 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -84,7 +84,7 @@ static int sysvipc_msg_proc_show(struct seq_file *s, void *it);
  * Also take into account the number of nsproxies created so far.
  * This should be done staying within the (MSGMNI , IPCMNI/nr_ipc_ns) range.
  */
-static void recompute_msgmni(struct ipc_namespace *ns)
+void recompute_msgmni(struct ipc_namespace *ns)
 {
         struct sysinfo i;
         unsigned long allowed;
diff --git a/ipc/namespace.c b/ipc/namespace.c
index fe3c97aa99dc..f7a35be2e771 100644
--- a/ipc/namespace.c
+++ b/ipc/namespace.c
@@ -26,6 +26,8 @@ static struct ipc_namespace *clone_ipc_ns(struct ipc_namespace *old_ns)
         msg_init_ns(ns);
         shm_init_ns(ns);
 
+        register_ipcns_notifier(ns);
+
         kref_init(&ns->kref);
         return ns;
 }
@@ -81,6 +83,15 @@ void free_ipc_ns(struct kref *kref)
         struct ipc_namespace *ns;
 
         ns = container_of(kref, struct ipc_namespace, kref);
+        /*
+         * Unregistering the hotplug notifier at the beginning guarantees
+         * that the ipc namespace won't be freed while we are inside the
+         * callback routine. Since the blocking_notifier_chain_XXX routines
+         * hold a rw lock on the notifier list, unregister_ipcns_notifier()
+         * won't take the rw lock before blocking_notifier_call_chain() has
+         * released the rd lock.
+         */
+        unregister_ipcns_notifier(ns);
         sem_exit_ns(ns);
         msg_exit_ns(ns);
         shm_exit_ns(ns);
diff --git a/ipc/util.c b/ipc/util.c
index c27f0e92f489..2d545d7144a7 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -33,6 +33,7 @@
 #include <linux/audit.h>
 #include <linux/nsproxy.h>
 #include <linux/rwsem.h>
+#include <linux/memory.h>
 #include <linux/ipc_namespace.h>
 
 #include <asm/unistd.h>
@@ -55,11 +56,41 @@ struct ipc_namespace init_ipc_ns = {
 atomic_t nr_ipc_ns = ATOMIC_INIT(1);
 
 
+#ifdef CONFIG_MEMORY_HOTPLUG
+
+static int ipc_memory_callback(struct notifier_block *self,
+                                unsigned long action, void *arg)
+{
+        switch (action) {
+        case MEM_ONLINE:    /* memory successfully brought online */
+        case MEM_OFFLINE:   /* or offline: it's time to recompute msgmni */
+                /*
+                 * This is done by invoking the ipcns notifier chain with the
+                 * IPC_MEMCHANGED event.
+                 */
+                ipcns_notify(IPCNS_MEMCHANGED);
+                break;
+        case MEM_GOING_ONLINE:
+        case MEM_GOING_OFFLINE:
+        case MEM_CANCEL_ONLINE:
+        case MEM_CANCEL_OFFLINE:
+        default:
+                break;
+        }
+
+        return NOTIFY_OK;
+}
+
+#endif /* CONFIG_MEMORY_HOTPLUG */
+
 /**
  *      ipc_init        -       initialise IPC subsystem
  *
  *      The various system5 IPC resources (semaphores, messages and shared
  *      memory) are initialised
+ *      A callback routine is registered into the memory hotplug notifier
+ *      chain: since msgmni scales to lowmem this callback routine will be
+ *      called upon successful memory add / remove to recompute msmgni.
  */
  
 static int __init ipc_init(void)
@@ -67,6 +98,8 @@ static int __init ipc_init(void)
         sem_init();
         msg_init();
         shm_init();
+        hotplug_memory_notifier(ipc_memory_callback, IPC_CALLBACK_PRI);
+        register_ipcns_notifier(&init_ipc_ns);
         return 0;
 }
 __initcall(ipc_init);
diff --git a/ipc/util.h b/ipc/util.h
index f37d160c98fe..0e3d79037a2a 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -124,6 +124,8 @@ extern void free_msg(struct msg_msg *msg);
 extern struct msg_msg *load_msg(const void __user *src, int len);
 extern int store_msg(void __user *dest, struct msg_msg *msg, int len);
 
+extern void recompute_msgmni(struct ipc_namespace *);
+
 static inline int ipc_buildid(int id, int seq)
 {
         return SEQ_MULTIPLIER * seq + id;