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

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* 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 <[email protected]>
This commit is contained in:
Al Viro 2011-06-08 21:13:01 -04:00
commit a685e08987
8 changed files with 55 additions and 72 deletions
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37
fs/sysfs/mount.c
View file

@ -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;

2
fs/sysfs/sysfs.h
View file

@ -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;