ipc: recompute msgmni on ipc namespace creation/removal

Introduce a notification mechanism that aims at recomputing msgmni each time
an ipc namespace is created or removed.

The ipc namespace notifier chain already defined for memory hotplug management
is used for that purpose too.

Each time a new ipc namespace is allocated or an existing ipc namespace is
removed, the ipcns notifier chain is notified.  The callback routine for each
registered ipc namespace is then activated in order to recompute msgmni for
that namespace.

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>

3 files changed, 15 insertions, 2 deletions

diff --git a/ipc/Makefile b/ipc/Makefile
index 388e4d259f02..65c384395801 100644
--- a/ipc/Makefile
+++ b/ipc/Makefile
@@ -3,8 +3,7 @@
 #
 
 obj-$(CONFIG_SYSVIPC_COMPAT) += compat.o
-obj_mem-$(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) += util.o msgutil.o msg.o sem.o shm.o ipcns_notifier.o
 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
index 0786af6ce3ec..c7974609defc 100644
--- a/ipc/ipcns_notifier.c
+++ b/ipc/ipcns_notifier.c
@@ -29,6 +29,8 @@ static int ipcns_callback(struct notifier_block *self,
 
         switch (action) {
         case IPCNS_MEMCHANGED:   /* amount of lowmem has changed */
+        case IPCNS_CREATED:
+        case IPCNS_REMOVED:
                 /*
                  * It's time to recompute msgmni
                  */
diff --git a/ipc/namespace.c b/ipc/namespace.c
index f7a35be2e771..9171d948751e 100644
--- a/ipc/namespace.c
+++ b/ipc/namespace.c
@@ -26,6 +26,12 @@ static struct ipc_namespace *clone_ipc_ns(struct ipc_namespace *old_ns)
         msg_init_ns(ns);
         shm_init_ns(ns);
 
+        /*
+         * msgmni has already been computed for the new ipc ns.
+         * Thus, do the ipcns creation notification before registering that
+         * new ipcns in the chain.
+         */
+        ipcns_notify(IPCNS_CREATED);
         register_ipcns_notifier(ns);
 
         kref_init(&ns->kref);
@@ -97,4 +103,10 @@ void free_ipc_ns(struct kref *kref)
         shm_exit_ns(ns);
         kfree(ns);
         atomic_dec(&nr_ipc_ns);
+
+        /*
+         * Do the ipcns removal notification after decrementing nr_ipc_ns in
+         * order to have a correct value when recomputing msgmni.
+         */
+        ipcns_notify(IPCNS_REMOVED);
 }