Delay struct net freeing while there's a sysfs instance refering to it

	* new refcount in struct net, controlling actual freeing of the memory
	* new method in kobj_ns_type_operations (->drop_ns())
	* ->current_ns() semantics change - it's supposed to be followed by
corresponding ->drop_ns().  For struct net in case of CONFIG_NET_NS it bumps
the new refcount; net_drop_ns() decrements it and calls net_free() if the
last reference has been dropped.  Method renamed to ->grab_current_ns().
	* old net_free() callers call net_drop_ns() instead.
	* sysfs_exit_ns() is gone, along with a large part of callchain
leading to it; now that the references stored in ->ns[...] stay valid we
do not need to hunt them down and replace them with NULL.  That fixes
problems in sysfs_lookup() and sysfs_readdir(), along with getting rid
of sb->s_instances abuse.

	Note that struct net *shutdown* logics has not changed - net_cleanup()
is called exactly when it used to be called.  The only thing postponed by
having a sysfs instance refering to that struct net is actual freeing of
memory occupied by struct net.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 12 insertions, 27 deletions

diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index 266895783b47..e34f0d99ea4e 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -95,6 +95,14 @@ static int sysfs_set_super(struct super_block *sb, void *data)
         return error;
 }
 
+static void free_sysfs_super_info(struct sysfs_super_info *info)
+{
+        int type;
+        for (type = KOBJ_NS_TYPE_NONE; type < KOBJ_NS_TYPES; type++)
+                kobj_ns_drop(type, info->ns[type]);
+        kfree(info);
+}
+
 static struct dentry *sysfs_mount(struct file_system_type *fs_type,
         int flags, const char *dev_name, void *data)
 {
@@ -108,11 +116,11 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
                 return ERR_PTR(-ENOMEM);
 
         for (type = KOBJ_NS_TYPE_NONE; type < KOBJ_NS_TYPES; type++)
-                info->ns[type] = kobj_ns_current(type);
+                info->ns[type] = kobj_ns_grab_current(type);
 
         sb = sget(fs_type, sysfs_test_super, sysfs_set_super, info);
         if (IS_ERR(sb) || sb->s_fs_info != info)
-                kfree(info);
+                free_sysfs_super_info(info);
         if (IS_ERR(sb))
                 return ERR_CAST(sb);
         if (!sb->s_root) {
@@ -131,12 +139,11 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
 static void sysfs_kill_sb(struct super_block *sb)
 {
         struct sysfs_super_info *info = sysfs_info(sb);
-
         /* Remove the superblock from fs_supers/s_instances
          * so we can't find it, before freeing sysfs_super_info.
          */
         kill_anon_super(sb);
-        kfree(info);
+        free_sysfs_super_info(info);
 }
 
 static struct file_system_type sysfs_fs_type = {
@@ -145,28 +152,6 @@ static struct file_system_type sysfs_fs_type = {
         .kill_sb        = sysfs_kill_sb,
 };
 
-void sysfs_exit_ns(enum kobj_ns_type type, const void *ns)
-{
-        struct super_block *sb;
-
-        mutex_lock(&sysfs_mutex);
-        spin_lock(&sb_lock);
-        list_for_each_entry(sb, &sysfs_fs_type.fs_supers, s_instances) {
-                struct sysfs_super_info *info = sysfs_info(sb);
-                /*
-                 * If we see a superblock on the fs_supers/s_instances
-                 * list the unmount has not completed and sb->s_fs_info
-                 * points to a valid struct sysfs_super_info.
-                 */
-                /* Ignore superblocks with the wrong ns */
-                if (info->ns[type] != ns)
-                        continue;
-                info->ns[type] = NULL;
-        }
-        spin_unlock(&sb_lock);
-        mutex_unlock(&sysfs_mutex);
-}
-
 int __init sysfs_init(void)
 {
         int err = -ENOMEM;
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 3d28af31d863..2ed2404f3113 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -136,7 +136,7 @@ struct sysfs_addrm_cxt {
  * instance).
  */
 struct sysfs_super_info {
-        const void *ns[KOBJ_NS_TYPES];
+        void *ns[KOBJ_NS_TYPES];
 };
 #define sysfs_info(SB) ((struct sysfs_super_info *)(SB->s_fs_info))
 extern struct sysfs_dirent sysfs_root;