ipcns: extract create_ipc_ns()

[safe/jmp/linux-2.6] / ipc / namespace.c

diff --git a/ipc/namespace.c b/ipc/namespace.c
index 4b4dc6d..231ee53 100644 (file)
--- a/ipc/namespace.c
+++ b/ipc/namespace.c
@@ -9,23 +9,31 @@
 #include <linux/rcupdate.h>
 #include <linux/nsproxy.h>
 #include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/mount.h>
 
 #include "util.h"
 
-static struct ipc_namespace *clone_ipc_ns(struct ipc_namespace *old_ns)
+static struct ipc_namespace *create_ipc_ns(void)
 {
        struct ipc_namespace *ns;
+       int err;
 
        ns = kmalloc(sizeof(struct ipc_namespace), GFP_KERNEL);
        if (ns == NULL)
                return ERR_PTR(-ENOMEM);
 
+       atomic_set(&ns->count, 1);
+       err = mq_init_ns(ns);
+       if (err) {
+               kfree(ns);
+               return ERR_PTR(err);
+       }
        atomic_inc(&nr_ipc_ns);
 
        sem_init_ns(ns);
        msg_init_ns(ns);
        shm_init_ns(ns);
-       mq_init_ns(ns);
 
        /*
         * msgmni has already been computed for the new ipc ns.
@@ -35,24 +43,14 @@ static struct ipc_namespace *clone_ipc_ns(struct ipc_namespace *old_ns)
        ipcns_notify(IPCNS_CREATED);
        register_ipcns_notifier(ns);
 
-       kref_init(&ns->kref);
        return ns;
 }
 
 struct ipc_namespace *copy_ipcs(unsigned long flags, struct ipc_namespace *ns)
 {
-       struct ipc_namespace *new_ns;
-
-       BUG_ON(!ns);
-       get_ipc_ns(ns);
-
        if (!(flags & CLONE_NEWIPC))
-               return ns;
-
-       new_ns = clone_ipc_ns(ns);
-
-       put_ipc_ns(ns);
-       return new_ns;
+               return get_ipc_ns(ns);
+       return create_ipc_ns();
 }
 
 /*
@@ -85,11 +83,34 @@ void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
        up_write(&ids->rw_mutex);
 }
 
-void free_ipc_ns(struct kref *kref)
+/*
+ * put_ipc_ns - drop a reference to an ipc namespace.
+ * @ns: the namespace to put
+ *
+ * If this is the last task in the namespace exiting, and
+ * it is dropping the refcount to 0, then it can race with
+ * a task in another ipc namespace but in a mounts namespace
+ * which has this ipcns's mqueuefs mounted, doing some action
+ * with one of the mqueuefs files.  That can raise the refcount.
+ * So dropping the refcount, and raising the refcount when
+ * accessing it through the VFS, are protected with mq_lock.
+ *
+ * (Clearly, a task raising the refcount on its own ipc_ns
+ * needn't take mq_lock since it can't race with the last task
+ * in the ipcns exiting).
+ */
+void put_ipc_ns(struct ipc_namespace *ns)
 {
-       struct ipc_namespace *ns;
+       if (atomic_dec_and_lock(&ns->count, &mq_lock)) {
+               mq_clear_sbinfo(ns);
+               spin_unlock(&mq_lock);
+               mq_put_mnt(ns);
+               free_ipc_ns(ns);
+       }
+}
 
-       ns = container_of(kref, struct ipc_namespace, kref);
+void free_ipc_ns(struct ipc_namespace *ns)
+{
        /*
         * Unregistering the hotplug notifier at the beginning guarantees
         * that the ipc namespace won't be freed while we are inside the
@@ -102,7 +123,6 @@ void free_ipc_ns(struct kref *kref)
        sem_exit_ns(ns);
        msg_exit_ns(ns);
        shm_exit_ns(ns);
-       mq_exit_ns(ns);
        kfree(ns);
        atomic_dec(&nr_ipc_ns);