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Date:   Sun, 18 Nov 2018 20:23:43 -0800
From:   Andrei Vagin <avagin@gmail.com>
To:     David Howells <dhowells@redhat.com>
Cc:     viro@zeniv.linux.org.uk,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Tejun Heo <tj@kernel.org>, Li Zefan <lizefan@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>, cgroups@vger.kernel.org,
        fenghua.yu@intel.com, torvalds@linux-foundation.org,
        ebiederm@xmission.com, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, mszeredi@redhat.com
Subject: Re: [PATCH 21/34] kernfs, sysfs, cgroup, intel_rdt: Support
 fs_context [ver #12]
Message-ID: <20181119042340.GA31532@gmail.com>
References: <153754740781.17872.7869536526927736855.stgit@warthog.procyon.org.uk>
 <153754758187.17872.2791003837321822804.stgit@warthog.procyon.org.uk>
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On Fri, Sep 21, 2018 at 05:33:01PM +0100, David Howells wrote:
> Make kernfs support superblock creation/mount/remount with fs_context.
> 
> This requires that sysfs, cgroup and intel_rdt, which are built on kernfs,
> be made to support fs_context also.
> 
> Notes:
> 
>  (1) A kernfs_fs_context struct is created to wrap fs_context and the
>      kernfs mount parameters are moved in here (or are in fs_context).
> 
>  (2) kernfs_mount{,_ns}() are made into kernfs_get_tree().  The extra
>      namespace tag parameter is passed in the context if desired
> 
>  (3) kernfs_free_fs_context() is provided as a destructor for the
>      kernfs_fs_context struct, but for the moment it does nothing except
>      get called in the right places.
> 
>  (4) sysfs doesn't wrap kernfs_fs_context since it has no parameters to
>      pass, but possibly this should be done anyway in case someone wants to
>      add a parameter in future.
> 
>  (5) A cgroup_fs_context struct is created to wrap kernfs_fs_context and
>      the cgroup v1 and v2 mount parameters are all moved there.
> 
>  (6) cgroup1 parameter parsing error messages are now handled by invalf(),
>      which allows userspace to collect them directly.
> 
>  (7) cgroup1 parameter cleanup is now done in the context destructor rather
>      than in the mount/get_tree and remount functions.
> 
> Weirdies:
> 
>  (*) cgroup_do_get_tree() calls cset_cgroup_from_root() with locks held,
>      but then uses the resulting pointer after dropping the locks.  I'm
>      told this is okay and needs commenting.
> 
>  (*) The cgroup refcount web.  This really needs documenting.
> 
>  (*) cgroup2 only has one root?
> 
> Add a suggestion from Thomas Gleixner in which the RDT enablement code is
> placed into its own function.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> cc: Tejun Heo <tj@kernel.org>
> cc: Li Zefan <lizefan@huawei.com>
> cc: Johannes Weiner <hannes@cmpxchg.org>
> cc: cgroups@vger.kernel.org
> cc: fenghua.yu@intel.com
> ---
> 
>  arch/x86/kernel/cpu/intel_rdt.h          |   15 +
>  arch/x86/kernel/cpu/intel_rdt_rdtgroup.c |  183 ++++++++++------
>  fs/kernfs/mount.c                        |   88 ++++----
>  fs/sysfs/mount.c                         |   67 ++++--
>  include/linux/cgroup.h                   |    3 
>  include/linux/kernfs.h                   |   39 ++-
>  kernel/cgroup/cgroup-internal.h          |   50 +++-
>  kernel/cgroup/cgroup-v1.c                |  345 ++++++++++++++++--------------
>  kernel/cgroup/cgroup.c                   |  264 +++++++++++++++--------
>  kernel/cgroup/cpuset.c                   |    4 
>  10 files changed, 640 insertions(+), 418 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/intel_rdt.h b/arch/x86/kernel/cpu/intel_rdt.h
> index 4e588f36228f..1461adc2c5e8 100644
> --- a/arch/x86/kernel/cpu/intel_rdt.h
> +++ b/arch/x86/kernel/cpu/intel_rdt.h
> @@ -33,6 +33,21 @@
>  #define RMID_VAL_ERROR			BIT_ULL(63)
>  #define RMID_VAL_UNAVAIL		BIT_ULL(62)
>  
> +
> +struct rdt_fs_context {
> +	struct kernfs_fs_context	kfc;
> +	bool				enable_cdpl2;
> +	bool				enable_cdpl3;
> +	bool				enable_mba_mbps;
> +};
> +
> +static inline struct rdt_fs_context *rdt_fc2context(struct fs_context *fc)
> +{
> +	struct kernfs_fs_context *kfc = fc->fs_private;
> +
> +	return container_of(kfc, struct rdt_fs_context, kfc);
> +}
> +
>  DECLARE_STATIC_KEY_FALSE(rdt_enable_key);
>  
>  /**
> diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
> index d6cb04c3a28b..34733a221669 100644
> --- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
> +++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
> @@ -24,6 +24,7 @@
>  #include <linux/cpu.h>
>  #include <linux/debugfs.h>
>  #include <linux/fs.h>
> +#include <linux/fs_parser.h>
>  #include <linux/sysfs.h>
>  #include <linux/kernfs.h>
>  #include <linux/seq_buf.h>
> @@ -1707,43 +1708,6 @@ static void cdp_disable_all(void)
>  		cdpl2_disable();
>  }
>  
> -static int parse_rdtgroupfs_options(char *data)
> -{
> -	char *token, *o = data;
> -	int ret = 0;
> -
> -	while ((token = strsep(&o, ",")) != NULL) {
> -		if (!*token) {
> -			ret = -EINVAL;
> -			goto out;
> -		}
> -
> -		if (!strcmp(token, "cdp")) {
> -			ret = cdpl3_enable();
> -			if (ret)
> -				goto out;
> -		} else if (!strcmp(token, "cdpl2")) {
> -			ret = cdpl2_enable();
> -			if (ret)
> -				goto out;
> -		} else if (!strcmp(token, "mba_MBps")) {
> -			ret = set_mba_sc(true);
> -			if (ret)
> -				goto out;
> -		} else {
> -			ret = -EINVAL;
> -			goto out;
> -		}
> -	}
> -
> -	return 0;
> -
> -out:
> -	pr_err("Invalid mount option \"%s\"\n", token);
> -
> -	return ret;
> -}
> -
>  /*
>   * We don't allow rdtgroup directories to be created anywhere
>   * except the root directory. Thus when looking for the rdtgroup
> @@ -1815,13 +1779,27 @@ static int mkdir_mondata_all(struct kernfs_node *parent_kn,
>  			     struct rdtgroup *prgrp,
>  			     struct kernfs_node **mon_data_kn);
>  
> -static struct dentry *rdt_mount(struct file_system_type *fs_type,
> -				int flags, const char *unused_dev_name,
> -				void *data, size_t data_size)
> +static int rdt_enable_ctx(struct rdt_fs_context *ctx)
> +{
> +	int ret = 0;
> +
> +	if (ctx->enable_cdpl2)
> +		ret = cdpl2_enable();
> +
> +	if (!ret && ctx->enable_cdpl3)
> +		ret = cdpl3_enable();
> +
> +	if (!ret && ctx->enable_mba_mbps)
> +		ret = set_mba_sc(true);
> +
> +	return ret;
> +}
> +
> +static int rdt_get_tree(struct fs_context *fc)
>  {
> +	struct rdt_fs_context *ctx = rdt_fc2context(fc);
>  	struct rdt_domain *dom;
>  	struct rdt_resource *r;
> -	struct dentry *dentry;
>  	int ret;
>  
>  	cpus_read_lock();
> @@ -1830,53 +1808,42 @@ static struct dentry *rdt_mount(struct file_system_type *fs_type,
>  	 * resctrl file system can only be mounted once.
>  	 */
>  	if (static_branch_unlikely(&rdt_enable_key)) {
> -		dentry = ERR_PTR(-EBUSY);
> +		ret = -EBUSY;
>  		goto out;
>  	}
>  
> -	ret = parse_rdtgroupfs_options(data);
> -	if (ret) {
> -		dentry = ERR_PTR(ret);
> +	ret = rdt_enable_ctx(ctx);
> +	if (ret < 0)
>  		goto out_cdp;
> -	}
>  
>  	closid_init();
>  
>  	ret = rdtgroup_create_info_dir(rdtgroup_default.kn);
> -	if (ret) {
> -		dentry = ERR_PTR(ret);
> -		goto out_cdp;
> -	}
> +	if (ret < 0)
> +		goto out_mba;
>  
>  	if (rdt_mon_capable) {
>  		ret = mongroup_create_dir(rdtgroup_default.kn,
>  					  NULL, "mon_groups",
>  					  &kn_mongrp);
> -		if (ret) {
> -			dentry = ERR_PTR(ret);
> +		if (ret < 0)
>  			goto out_info;
> -		}
>  		kernfs_get(kn_mongrp);
>  
>  		ret = mkdir_mondata_all(rdtgroup_default.kn,
>  					&rdtgroup_default, &kn_mondata);
> -		if (ret) {
> -			dentry = ERR_PTR(ret);
> +		if (ret < 0)
>  			goto out_mongrp;
> -		}
>  		kernfs_get(kn_mondata);
>  		rdtgroup_default.mon.mon_data_kn = kn_mondata;
>  	}
>  
>  	ret = rdt_pseudo_lock_init();
> -	if (ret) {
> -		dentry = ERR_PTR(ret);
> +	if (ret)
>  		goto out_mondata;
> -	}
>  
> -	dentry = kernfs_mount(fs_type, flags, rdt_root,
> -			      RDTGROUP_SUPER_MAGIC, NULL);
> -	if (IS_ERR(dentry))
> +	ret = kernfs_get_tree(fc);
> +	if (ret < 0)
>  		goto out_psl;
>  
>  	if (rdt_alloc_capable)
> @@ -1905,14 +1872,97 @@ static struct dentry *rdt_mount(struct file_system_type *fs_type,
>  		kernfs_remove(kn_mongrp);
>  out_info:
>  	kernfs_remove(kn_info);
> +out_mba:
> +	if (ctx->enable_mba_mbps)
> +		set_mba_sc(false);
>  out_cdp:
>  	cdp_disable_all();
>  out:
>  	rdt_last_cmd_clear();
>  	mutex_unlock(&rdtgroup_mutex);
>  	cpus_read_unlock();
> +	return ret;
> +}
> +
> +enum rdt_param {
> +	Opt_cdp,
> +	Opt_cdpl2,
> +	Opt_mba_mpbs,
> +	nr__rdt_params
> +};
> +
> +static const struct fs_parameter_spec rdt_param_specs[nr__rdt_params] = {
> +	[Opt_cdp]	= { fs_param_is_flag },
> +	[Opt_cdpl2]	= { fs_param_is_flag },
> +	[Opt_mba_mpbs]	= { fs_param_is_flag },
> +};
> +
> +static const char *const rdt_param_keys[nr__rdt_params] = {
> +	[Opt_cdp]	= "cdp",
> +	[Opt_cdpl2]	= "cdpl2",
> +	[Opt_mba_mpbs]	= "mba_mbps",
> +};
> +
> +static const struct fs_parameter_description rdt_fs_parameters = {
> +	.name		= "rdt",
> +	.nr_params	= nr__rdt_params,
> +	.keys		= rdt_param_keys,
> +	.specs		= rdt_param_specs,
> +	.no_source	= true,
> +};
> +
> +static int rdt_parse_param(struct fs_context *fc, struct fs_parameter *param)
> +{
> +	struct rdt_fs_context *ctx = rdt_fc2context(fc);
> +	struct fs_parse_result result;
> +	int opt;
>  
> -	return dentry;
> +	opt = fs_parse(fc, &rdt_fs_parameters, param, &result);
> +	if (opt < 0)
> +		return opt;
> +
> +	switch (opt) {
> +	case Opt_cdp:
> +		ctx->enable_cdpl3 = true;
> +		return 0;
> +	case Opt_cdpl2:
> +		ctx->enable_cdpl2 = true;
> +		return 0;
> +	case Opt_mba_mpbs:
> +		ctx->enable_mba_mbps = true;
> +		return 0;
> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static void rdt_fs_context_free(struct fs_context *fc)
> +{
> +	struct rdt_fs_context *ctx = rdt_fc2context(fc);
> +
> +	kernfs_free_fs_context(fc);
> +	kfree(ctx);
> +}
> +
> +static const struct fs_context_operations rdt_fs_context_ops = {
> +	.free		= rdt_fs_context_free,
> +	.parse_param	= rdt_parse_param,
> +	.get_tree	= rdt_get_tree,
> +};
> +
> +static int rdt_init_fs_context(struct fs_context *fc, struct dentry *reference)
> +{
> +	struct rdt_fs_context *ctx;
> +
> +	ctx = kzalloc(sizeof(struct rdt_fs_context), GFP_KERNEL);
> +	if (!ctx)
> +		return -ENOMEM;
> +
> +	ctx->kfc.root = rdt_root;
> +	ctx->kfc.magic = RDTGROUP_SUPER_MAGIC;
> +	fc->fs_private = &ctx->kfc;
> +	fc->ops = &rdt_fs_context_ops;
> +	return 0;
>  }
>  
>  static int reset_all_ctrls(struct rdt_resource *r)
> @@ -2085,9 +2135,10 @@ static void rdt_kill_sb(struct super_block *sb)
>  }
>  
>  static struct file_system_type rdt_fs_type = {
> -	.name    = "resctrl",
> -	.mount   = rdt_mount,
> -	.kill_sb = rdt_kill_sb,
> +	.name			= "resctrl",
> +	.init_fs_context	= rdt_init_fs_context,
> +	.parameters		= &rdt_fs_parameters,
> +	.kill_sb		= rdt_kill_sb,
>  };
>  
>  static int mon_addfile(struct kernfs_node *parent_kn, const char *name,
> diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
> index f70e0b69e714..56742632956c 100644
> --- a/fs/kernfs/mount.c
> +++ b/fs/kernfs/mount.c
> @@ -22,14 +22,13 @@
>  
>  struct kmem_cache *kernfs_node_cache;
>  
> -static int kernfs_sop_remount_fs(struct super_block *sb, int *flags,
> -				 char *data, size_t data_size)
> +int kernfs_reconfigure(struct fs_context *fc)
>  {
> -	struct kernfs_root *root = kernfs_info(sb)->root;
> +	struct kernfs_root *root = kernfs_info(fc->root->d_sb)->root;
>  	struct kernfs_syscall_ops *scops = root->syscall_ops;
>  
> -	if (scops && scops->remount_fs)
> -		return scops->remount_fs(root, flags, data);
> +	if (scops && scops->reconfigure)
> +		return scops->reconfigure(root, fc);
>  	return 0;
>  }
>  
> @@ -61,7 +60,6 @@ const struct super_operations kernfs_sops = {
>  	.drop_inode	= generic_delete_inode,
>  	.evict_inode	= kernfs_evict_inode,
>  
> -	.remount_fs	= kernfs_sop_remount_fs,
>  	.show_options	= kernfs_sop_show_options,
>  	.show_path	= kernfs_sop_show_path,
>  };
> @@ -219,7 +217,7 @@ struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
>  	} while (true);
>  }
>  
> -static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
> +static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
>  {
>  	struct kernfs_super_info *info = kernfs_info(sb);
>  	struct inode *inode;
> @@ -230,7 +228,7 @@ static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
>  	sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
>  	sb->s_blocksize = PAGE_SIZE;
>  	sb->s_blocksize_bits = PAGE_SHIFT;
> -	sb->s_magic = magic;
> +	sb->s_magic = kfc->magic;
>  	sb->s_op = &kernfs_sops;
>  	sb->s_xattr = kernfs_xattr_handlers;
>  	if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
> @@ -257,21 +255,20 @@ static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
>  	return 0;
>  }
>  
> -static int kernfs_test_super(struct super_block *sb, void *data)
> +static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
>  {
>  	struct kernfs_super_info *sb_info = kernfs_info(sb);
> -	struct kernfs_super_info *info = data;
> +	struct kernfs_super_info *info = fc->s_fs_info;
>  
>  	return sb_info->root == info->root && sb_info->ns == info->ns;
>  }
>  
> -static int kernfs_set_super(struct super_block *sb, void *data)
> +static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
>  {
> -	int error;
> -	error = set_anon_super(sb, data);
> -	if (!error)
> -		sb->s_fs_info = data;
> -	return error;
> +	struct kernfs_fs_context *kfc = fc->fs_private;
> +
> +	kfc->ns_tag = NULL;
> +	return set_anon_super_fc(sb, fc);
>  }
>  
>  /**
> @@ -288,63 +285,60 @@ const void *kernfs_super_ns(struct super_block *sb)
>  }
>  
>  /**
> - * kernfs_mount_ns - kernfs mount helper
> - * @fs_type: file_system_type of the fs being mounted
> - * @flags: mount flags specified for the mount
> - * @root: kernfs_root of the hierarchy being mounted
> - * @magic: file system specific magic number
> - * @new_sb_created: tell the caller if we allocated a new superblock
> - * @ns: optional namespace tag of the mount
> - *
> - * This is to be called from each kernfs user's file_system_type->mount()
> - * implementation, which should pass through the specified @fs_type and
> - * @flags, and specify the hierarchy and namespace tag to mount via @root
> - * and @ns, respectively.
> + * kernfs_get_tree - kernfs filesystem access/retrieval helper
> + * @fc: The filesystem context.
>   *
> - * The return value can be passed to the vfs layer verbatim.
> + * This is to be called from each kernfs user's fs_context->ops->get_tree()
> + * implementation, which should set the specified ->@fs_type and ->@flags, and
> + * specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
> + * respectively.
>   */
> -struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
> -				struct kernfs_root *root, unsigned long magic,
> -				bool *new_sb_created, const void *ns)
> +int kernfs_get_tree(struct fs_context *fc)
>  {
> +	struct kernfs_fs_context *kfc = fc->fs_private;
>  	struct super_block *sb;
>  	struct kernfs_super_info *info;
>  	int error;
>  
>  	info = kzalloc(sizeof(*info), GFP_KERNEL);
>  	if (!info)
> -		return ERR_PTR(-ENOMEM);
> +		return -ENOMEM;
>  
> -	info->root = root;
> -	info->ns = ns;
> +	info->root = kfc->root;
> +	info->ns = kfc->ns_tag;
>  	INIT_LIST_HEAD(&info->node);
>  
> -	sb = sget_userns(fs_type, kernfs_test_super, kernfs_set_super, flags,
> -			 &init_user_ns, info);
> -	if (IS_ERR(sb) || sb->s_fs_info != info)
> -		kfree(info);
> +	fc->s_fs_info = info;
> +	sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
>  	if (IS_ERR(sb))
> -		return ERR_CAST(sb);
> -
> -	if (new_sb_created)
> -		*new_sb_created = !sb->s_root;
> +		return PTR_ERR(sb);
>  
>  	if (!sb->s_root) {
>  		struct kernfs_super_info *info = kernfs_info(sb);
>  
> -		error = kernfs_fill_super(sb, magic);
> +		kfc->new_sb_created = true;
> +
> +		error = kernfs_fill_super(sb, kfc);
>  		if (error) {
>  			deactivate_locked_super(sb);
> -			return ERR_PTR(error);
> +			return error;
>  		}
>  		sb->s_flags |= SB_ACTIVE;
>  
>  		mutex_lock(&kernfs_mutex);
> -		list_add(&info->node, &root->supers);
> +		list_add(&info->node, &info->root->supers);
>  		mutex_unlock(&kernfs_mutex);
>  	}
>  
> -	return dget(sb->s_root);
> +	fc->root = dget(sb->s_root);
> +	return 0;
> +}
> +
> +void kernfs_free_fs_context(struct fs_context *fc)
> +{
> +	/* Note that we don't deal with kfc->ns_tag here. */
> +	kfree(fc->s_fs_info);
> +	fc->s_fs_info = NULL;
>  }
>  
>  /**
> diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
> index 77302c35b0ff..1e1c0ccc6a36 100644
> --- a/fs/sysfs/mount.c
> +++ b/fs/sysfs/mount.c
> @@ -13,6 +13,7 @@
>  #include <linux/magic.h>
>  #include <linux/mount.h>
>  #include <linux/init.h>
> +#include <linux/slab.h>
>  #include <linux/user_namespace.h>
>  
>  #include "sysfs.h"
> @@ -20,27 +21,55 @@
>  static struct kernfs_root *sysfs_root;
>  struct kernfs_node *sysfs_root_kn;
>  
> -static struct dentry *sysfs_mount(struct file_system_type *fs_type,
> -	int flags, const char *dev_name, void *data, size_t data_size)
> +static int sysfs_get_tree(struct fs_context *fc)
>  {
> -	struct dentry *root;
> -	void *ns;
> -	bool new_sb = false;
> +	struct kernfs_fs_context *kfc = fc->fs_private;
> +	int ret;
>  
> -	if (!(flags & SB_KERNMOUNT)) {
> +	ret = kernfs_get_tree(fc);
> +	if (ret)
> +		return ret;
> +
> +	if (kfc->new_sb_created)
> +		fc->root->d_sb->s_iflags |= SB_I_USERNS_VISIBLE;
> +	return 0;
> +}
> +
> +static void sysfs_fs_context_free(struct fs_context *fc)
> +{
> +	struct kernfs_fs_context *kfc = fc->fs_private;
> +
> +	if (kfc->ns_tag)
> +		kobj_ns_drop(KOBJ_NS_TYPE_NET, kfc->ns_tag);
> +	kernfs_free_fs_context(fc);
> +	kfree(kfc);
> +}
> +
> +static const struct fs_context_operations sysfs_fs_context_ops = {
> +	.free		= sysfs_fs_context_free,
> +	.get_tree	= sysfs_get_tree,
> +};
> +
> +static int sysfs_init_fs_context(struct fs_context *fc,
> +				 struct dentry *reference)
> +{
> +	struct kernfs_fs_context *kfc;
> +
> +	if (!(fc->sb_flags & SB_KERNMOUNT)) {
>  		if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
> -			return ERR_PTR(-EPERM);
> +			return -EPERM;
>  	}
>  
> -	ns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
> -	root = kernfs_mount_ns(fs_type, flags, sysfs_root,
> -				SYSFS_MAGIC, &new_sb, ns);
> -	if (!new_sb)
> -		kobj_ns_drop(KOBJ_NS_TYPE_NET, ns);
> -	else if (!IS_ERR(root))
> -		root->d_sb->s_iflags |= SB_I_USERNS_VISIBLE;
> +	kfc = kzalloc(sizeof(struct kernfs_fs_context), GFP_KERNEL);
> +	if (!kfc)
> +		return -ENOMEM;
>  
> -	return root;
> +	kfc->ns_tag = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
> +	kfc->root = sysfs_root;
> +	kfc->magic = SYSFS_MAGIC;
> +	fc->fs_private = kfc;
> +	fc->ops = &sysfs_fs_context_ops;
> +	return 0;
>  }
>  
>  static void sysfs_kill_sb(struct super_block *sb)
> @@ -52,10 +81,10 @@ static void sysfs_kill_sb(struct super_block *sb)
>  }
>  
>  static struct file_system_type sysfs_fs_type = {
> -	.name		= "sysfs",
> -	.mount		= sysfs_mount,
> -	.kill_sb	= sysfs_kill_sb,
> -	.fs_flags	= FS_USERNS_MOUNT,
> +	.name			= "sysfs",
> +	.init_fs_context	= sysfs_init_fs_context,
> +	.kill_sb		= sysfs_kill_sb,
> +	.fs_flags		= FS_USERNS_MOUNT,
>  };
>  
>  int __init sysfs_init(void)
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 32c553556bbd..13b6379648ec 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -859,10 +859,11 @@ copy_cgroup_ns(unsigned long flags, struct user_namespace *user_ns,
>  
>  #endif /* !CONFIG_CGROUPS */
>  
> -static inline void get_cgroup_ns(struct cgroup_namespace *ns)
> +static inline struct cgroup_namespace *get_cgroup_ns(struct cgroup_namespace *ns)
>  {
>  	if (ns)
>  		refcount_inc(&ns->count);
> +	return ns;
>  }
>  
>  static inline void put_cgroup_ns(struct cgroup_namespace *ns)
> diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
> index 0f6bb8e1bc83..051709212f55 100644
> --- a/include/linux/kernfs.h
> +++ b/include/linux/kernfs.h
> @@ -17,6 +17,7 @@
>  #include <linux/atomic.h>
>  #include <linux/uidgid.h>
>  #include <linux/wait.h>
> +#include <linux/fs_context.h>
>  
>  struct file;
>  struct dentry;
> @@ -27,6 +28,7 @@ struct super_block;
>  struct file_system_type;
>  struct fs_context;
>  
> +struct kernfs_fs_context;
>  struct kernfs_open_node;
>  struct kernfs_iattrs;
>  
> @@ -168,7 +170,7 @@ struct kernfs_node {
>   * kernfs_node parameter.
>   */
>  struct kernfs_syscall_ops {
> -	int (*remount_fs)(struct kernfs_root *root, int *flags, char *data);
> +	int (*reconfigure)(struct kernfs_root *root, struct fs_context *fc);
>  	int (*show_options)(struct seq_file *sf, struct kernfs_root *root);
>  
>  	int (*mkdir)(struct kernfs_node *parent, const char *name,
> @@ -269,6 +271,18 @@ struct kernfs_ops {
>  #endif
>  };
>  
> +/*
> + * The kernfs superblock creation/mount parameter context.
> + */
> +struct kernfs_fs_context {
> +	struct kernfs_root	*root;		/* Root of the hierarchy being mounted */
> +	void			*ns_tag;	/* Namespace tag of the mount (or NULL) */
> +	unsigned long		magic;		/* File system specific magic number */
> +
> +	/* The following are set/used by kernfs_mount() */
> +	bool			new_sb_created;	/* Set to T if we allocated a new sb */
> +};
> +
>  #ifdef CONFIG_KERNFS
>  
>  static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
> @@ -354,9 +368,8 @@ int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr);
>  void kernfs_notify(struct kernfs_node *kn);
>  
>  const void *kernfs_super_ns(struct super_block *sb);
> -struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
> -			       struct kernfs_root *root, unsigned long magic,
> -			       bool *new_sb_created, const void *ns);
> +int kernfs_get_tree(struct fs_context *fc);
> +void kernfs_free_fs_context(struct fs_context *fc);
>  void kernfs_kill_sb(struct super_block *sb);
>  struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns);
>  int kernfs_reconfigure(struct fs_context *fc);
> @@ -461,11 +474,10 @@ static inline void kernfs_notify(struct kernfs_node *kn) { }
>  static inline const void *kernfs_super_ns(struct super_block *sb)
>  { return NULL; }
>  
> -static inline struct dentry *
> -kernfs_mount_ns(struct file_system_type *fs_type, int flags,
> -		struct kernfs_root *root, unsigned long magic,
> -		bool *new_sb_created, const void *ns)
> -{ return ERR_PTR(-ENOSYS); }
> +static inline int kernfs_get_tree(struct fs_context *fc)
> +{ return -ENOSYS; }
> +
> +static inline void kernfs_free_fs_context(struct fs_context *fc) { }
>  
>  static inline void kernfs_kill_sb(struct super_block *sb) { }
>  
> @@ -547,13 +559,4 @@ static inline int kernfs_rename(struct kernfs_node *kn,
>  	return kernfs_rename_ns(kn, new_parent, new_name, NULL);
>  }
>  
> -static inline struct dentry *
> -kernfs_mount(struct file_system_type *fs_type, int flags,
> -		struct kernfs_root *root, unsigned long magic,
> -		bool *new_sb_created)
> -{
> -	return kernfs_mount_ns(fs_type, flags, root,
> -				magic, new_sb_created, NULL);
> -}
> -
>  #endif	/* __LINUX_KERNFS_H */
> diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
> index 75568fcf2180..35012d2aca97 100644
> --- a/kernel/cgroup/cgroup-internal.h
> +++ b/kernel/cgroup/cgroup-internal.h
> @@ -34,6 +34,33 @@ extern char trace_cgroup_path[TRACE_CGROUP_PATH_LEN];
>  		}							\
>  	} while (0)
>  
> +/*
> + * The cgroup filesystem superblock creation/mount context.
> + */
> +struct cgroup_fs_context {
> +	struct kernfs_fs_context kfc;
> +	struct cgroup_root	*root;
> +	struct cgroup_namespace	*ns;
> +	u8		version;		/* cgroups version */
> +	unsigned int	flags;			/* CGRP_ROOT_* flags */
> +
> +	/* cgroup1 bits */
> +	bool		cpuset_clone_children;
> +	bool		none;			/* User explicitly requested empty subsystem */
> +	bool		all_ss;			/* Seen 'all' option */
> +	bool		one_ss;			/* Seen 'none' option */
> +	u16		subsys_mask;		/* Selected subsystems */
> +	char		*name;			/* Hierarchy name */
> +	char		*release_agent;		/* Path for release notifications */
> +};
> +
> +static inline struct cgroup_fs_context *cgroup_fc2context(struct fs_context *fc)
> +{
> +	struct kernfs_fs_context *kfc = fc->fs_private;
> +
> +	return container_of(kfc, struct cgroup_fs_context, kfc);
> +}
> +
>  /*
>   * A cgroup can be associated with multiple css_sets as different tasks may
>   * belong to different cgroups on different hierarchies.  In the other
> @@ -115,16 +142,6 @@ struct cgroup_mgctx {
>  #define DEFINE_CGROUP_MGCTX(name)						\
>  	struct cgroup_mgctx name = CGROUP_MGCTX_INIT(name)
>  
> -struct cgroup_sb_opts {
> -	u16 subsys_mask;
> -	unsigned int flags;
> -	char *release_agent;
> -	bool cpuset_clone_children;
> -	char *name;
> -	/* User explicitly requested empty subsystem */
> -	bool none;
> -};
> -
>  extern struct mutex cgroup_mutex;
>  extern spinlock_t css_set_lock;
>  extern struct cgroup_subsys *cgroup_subsys[];
> @@ -195,12 +212,10 @@ int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
>  			  struct cgroup_namespace *ns);
>  
>  void cgroup_free_root(struct cgroup_root *root);
> -void init_cgroup_root(struct cgroup_root *root, struct cgroup_sb_opts *opts);
> +void init_cgroup_root(struct cgroup_fs_context *ctx);
>  int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask, int ref_flags);
>  int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask);
> -struct dentry *cgroup_do_mount(struct file_system_type *fs_type, int flags,
> -			       struct cgroup_root *root, unsigned long magic,
> -			       struct cgroup_namespace *ns);
> +int cgroup_do_get_tree(struct fs_context *fc);
>  
>  int cgroup_migrate_vet_dst(struct cgroup *dst_cgrp);
>  void cgroup_migrate_finish(struct cgroup_mgctx *mgctx);
> @@ -244,14 +259,15 @@ extern const struct proc_ns_operations cgroupns_operations;
>   */
>  extern struct cftype cgroup1_base_files[];
>  extern struct kernfs_syscall_ops cgroup1_kf_syscall_ops;
> +extern const struct fs_parameter_description cgroup1_fs_parameters;
>  
>  int proc_cgroupstats_show(struct seq_file *m, void *v);
>  bool cgroup1_ssid_disabled(int ssid);
>  void cgroup1_pidlist_destroy_all(struct cgroup *cgrp);
>  void cgroup1_release_agent(struct work_struct *work);
>  void cgroup1_check_for_release(struct cgroup *cgrp);
> -struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
> -			     void *data, unsigned long magic,
> -			     struct cgroup_namespace *ns);
> +int cgroup1_parse_param(struct fs_context *fc, struct fs_parameter *param);
> +int cgroup1_validate(struct fs_context *fc);
> +int cgroup1_get_tree(struct fs_context *fc);
>  
>  #endif /* __CGROUP_INTERNAL_H */
> diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
> index 51063e7a93c2..d8b325c3c2eb 100644
> --- a/kernel/cgroup/cgroup-v1.c
> +++ b/kernel/cgroup/cgroup-v1.c
> @@ -13,9 +13,12 @@
>  #include <linux/delayacct.h>
>  #include <linux/pid_namespace.h>
>  #include <linux/cgroupstats.h>
> +#include <linux/fs_parser.h>
>  
>  #include <trace/events/cgroup.h>
>  
> +#define cg_invalf(fc, fmt, ...) ({ pr_err(fmt, ## __VA_ARGS__); -EINVAL; })
> +
>  /*
>   * pidlists linger the following amount before being destroyed.  The goal
>   * is avoiding frequent destruction in the middle of consecutive read calls
> @@ -903,92 +906,61 @@ static int cgroup1_show_options(struct seq_file *seq, struct kernfs_root *kf_roo
>  	return 0;
>  }
>  
> -static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
> -{
> -	char *token, *o = data;
> -	bool all_ss = false, one_ss = false;
> -	u16 mask = U16_MAX;
> -	struct cgroup_subsys *ss;
> -	int nr_opts = 0;
> -	int i;
> -
> -#ifdef CONFIG_CPUSETS
> -	mask = ~((u16)1 << cpuset_cgrp_id);
> -#endif
> +enum cgroup1_param {
> +	Opt_all,
> +	Opt_clone_children,
> +	Opt_cpuset_v2_mode,
> +	Opt_name,
> +	Opt_none,
> +	Opt_noprefix,
> +	Opt_release_agent,
> +	Opt_xattr,
> +	nr__cgroup1_params
> +};
>  
> -	memset(opts, 0, sizeof(*opts));
> +static const struct fs_parameter_spec cgroup1_param_specs[nr__cgroup1_params] = {
> +	[Opt_all]		= { fs_param_is_flag },
> +	[Opt_clone_children]	= { fs_param_is_flag },
> +	[Opt_cpuset_v2_mode]	= { fs_param_is_flag },
> +	[Opt_name]		= { fs_param_is_string },
> +	[Opt_none]		= { fs_param_is_flag },
> +	[Opt_noprefix]		= { fs_param_is_flag },
> +	[Opt_release_agent]	= { fs_param_is_string },
> +	[Opt_xattr]		= { fs_param_is_flag },
> +};
>  
> -	while ((token = strsep(&o, ",")) != NULL) {
> -		nr_opts++;
> +static const char *const cgroup1_param_keys[nr__cgroup1_params] = {
> +	[Opt_all]		= "all",
> +	[Opt_clone_children]	= "clone_children",
> +	[Opt_cpuset_v2_mode]	= "cpuset_v2_mode",
> +	[Opt_name]		= "name",
> +	[Opt_none]		= "none",
> +	[Opt_noprefix]		= "noprefix",
> +	[Opt_release_agent]	= "release_agent",
> +	[Opt_xattr]		= "xattr",
> +};
>  
> -		if (!*token)
> -			return -EINVAL;
> -		if (!strcmp(token, "none")) {
> -			/* Explicitly have no subsystems */
> -			opts->none = true;
> -			continue;
> -		}
> -		if (!strcmp(token, "all")) {
> -			/* Mutually exclusive option 'all' + subsystem name */
> -			if (one_ss)
> -				return -EINVAL;
> -			all_ss = true;
> -			continue;
> -		}
> -		if (!strcmp(token, "noprefix")) {
> -			opts->flags |= CGRP_ROOT_NOPREFIX;
> -			continue;
> -		}
> -		if (!strcmp(token, "clone_children")) {
> -			opts->cpuset_clone_children = true;
> -			continue;
> -		}
> -		if (!strcmp(token, "cpuset_v2_mode")) {
> -			opts->flags |= CGRP_ROOT_CPUSET_V2_MODE;
> -			continue;
> -		}
> -		if (!strcmp(token, "xattr")) {
> -			opts->flags |= CGRP_ROOT_XATTR;
> -			continue;
> -		}
> -		if (!strncmp(token, "release_agent=", 14)) {
> -			/* Specifying two release agents is forbidden */
> -			if (opts->release_agent)
> -				return -EINVAL;
> -			opts->release_agent =
> -				kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL);
> -			if (!opts->release_agent)
> -				return -ENOMEM;
> -			continue;
> -		}
> -		if (!strncmp(token, "name=", 5)) {
> -			const char *name = token + 5;
> -			/* Can't specify an empty name */
> -			if (!strlen(name))
> -				return -EINVAL;
> -			/* Must match [\w.-]+ */
> -			for (i = 0; i < strlen(name); i++) {
> -				char c = name[i];
> -				if (isalnum(c))
> -					continue;
> -				if ((c == '.') || (c == '-') || (c == '_'))
> -					continue;
> -				return -EINVAL;
> -			}
> -			/* Specifying two names is forbidden */
> -			if (opts->name)
> -				return -EINVAL;
> -			opts->name = kstrndup(name,
> -					      MAX_CGROUP_ROOT_NAMELEN - 1,
> -					      GFP_KERNEL);
> -			if (!opts->name)
> -				return -ENOMEM;
> +const struct fs_parameter_description cgroup1_fs_parameters = {
> +	.name		= "cgroup1",
> +	.nr_params	= nr__cgroup1_params,
> +	.keys		= cgroup1_param_keys,
> +	.specs		= cgroup1_param_specs,
> +	.no_source	= true,
> +};
>  
> -			continue;
> -		}
> +int cgroup1_parse_param(struct fs_context *fc, struct fs_parameter *param)
> +{
> +	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
> +	struct cgroup_subsys *ss;
> +	struct fs_parse_result result;
> +	int opt, i;
>  
> +	opt = fs_parse(fc, &cgroup1_fs_parameters, param, &result);
> +	if (opt == -ENOPARAM) {
> +		if (strcmp(param->key, "source") == 0)
> +			return 0;
>  		for_each_subsys(ss, i) {
> -			if (strcmp(token, ss->legacy_name))
> +			if (strcmp(param->key, ss->legacy_name) != 0)
>  				continue;
>  			if (!cgroup_ssid_enabled(i))
>  				continue;
> @@ -996,75 +968,144 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
>  				continue;
>  
>  			/* Mutually exclusive option 'all' + subsystem name */
> -			if (all_ss)
> -				return -EINVAL;
> -			opts->subsys_mask |= (1 << i);
> -			one_ss = true;
> +			if (ctx->all_ss)
> +				return cg_invalf(fc, "cgroup1: subsys name conflicts with all");
> +			ctx->subsys_mask |= (1 << i);
> +			ctx->one_ss = true;
> +			return 0;
> +		}
>  
> -			break;
> +		return cg_invalf(fc, "cgroup1: Unknown subsys name '%s'", param->key);
> +	}
> +	if (opt < 0)
> +		return opt;
> +
> +	switch (opt) {
> +	case Opt_none:
> +		/* Explicitly have no subsystems */
> +		ctx->none = true;
> +		return 0;
> +	case Opt_all:
> +		/* Mutually exclusive option 'all' + subsystem name */
> +		if (ctx->one_ss)
> +			return cg_invalf(fc, "cgroup1: all conflicts with subsys name");
> +		ctx->all_ss = true;
> +		return 0;
> +	case Opt_noprefix:
> +		ctx->flags |= CGRP_ROOT_NOPREFIX;
> +		return 0;
> +	case Opt_clone_children:
> +		ctx->cpuset_clone_children = true;
> +		return 0;
> +	case Opt_cpuset_v2_mode:
> +		ctx->flags |= CGRP_ROOT_CPUSET_V2_MODE;
> +		return 0;
> +	case Opt_xattr:
> +		ctx->flags |= CGRP_ROOT_XATTR;
> +		return 0;
> +	case Opt_release_agent:
> +		/* Specifying two release agents is forbidden */
> +		if (ctx->release_agent)
> +			return cg_invalf(fc, "cgroup1: release_agent respecified");
> +		ctx->release_agent = param->string;
> +		param->string = NULL;
> +		if (!ctx->release_agent)
> +			return -ENOMEM;
> +		return 0;
> +
> +	case Opt_name:
> +		/* Can't specify an empty name */
> +		if (!param->size)
> +			return cg_invalf(fc, "cgroup1: Empty name");
> +		if (param->size > MAX_CGROUP_ROOT_NAMELEN - 1)
> +			return cg_invalf(fc, "cgroup1: Name too long");
> +		/* Must match [\w.-]+ */
> +		for (i = 0; i < param->size; i++) {
> +			char c = param->string[i];
> +			if (isalnum(c))
> +				continue;
> +			if ((c == '.') || (c == '-') || (c == '_'))
> +				continue;
> +			return cg_invalf(fc, "cgroup1: Invalid name");
>  		}
> -		if (i == CGROUP_SUBSYS_COUNT)
> -			return -ENOENT;
> +		/* Specifying two names is forbidden */
> +		if (ctx->name)
> +			return cg_invalf(fc, "cgroup1: name respecified");
> +		ctx->name = param->string;
> +		param->string = NULL;
> +		return 0;
>  	}
>  
> +	return 0;
> +}
> +
> +/*
> + * Validate the options that have been parsed.
> + */
> +int cgroup1_validate(struct fs_context *fc)
> +{
> +	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
> +	struct cgroup_subsys *ss;
> +	u16 mask = U16_MAX;
> +	int i;
> +
> +#ifdef CONFIG_CPUSETS
> +	mask = ~((u16)1 << cpuset_cgrp_id);
> +#endif
> +
>  	/*
>  	 * If the 'all' option was specified select all the subsystems,
>  	 * otherwise if 'none', 'name=' and a subsystem name options were
>  	 * not specified, let's default to 'all'
>  	 */
> -	if (all_ss || (!one_ss && !opts->none && !opts->name))
> +	if (ctx->all_ss || (!ctx->one_ss && !ctx->none && !ctx->name))
>  		for_each_subsys(ss, i)
>  			if (cgroup_ssid_enabled(i) && !cgroup1_ssid_disabled(i))
> -				opts->subsys_mask |= (1 << i);
> +				ctx->subsys_mask |= (1 << i);
>  
>  	/*
>  	 * We either have to specify by name or by subsystems. (So all
>  	 * empty hierarchies must have a name).
>  	 */
> -	if (!opts->subsys_mask && !opts->name)
> -		return -EINVAL;
> +	if (!ctx->subsys_mask && !ctx->name)
> +		return cg_invalf(fc, "cgroup1: Need name or subsystem set");
>  
>  	/*
>  	 * Option noprefix was introduced just for backward compatibility
>  	 * with the old cpuset, so we allow noprefix only if mounting just
>  	 * the cpuset subsystem.
>  	 */
> -	if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask))
> -		return -EINVAL;
> +	if ((ctx->flags & CGRP_ROOT_NOPREFIX) && (ctx->subsys_mask & mask))
> +		return cg_invalf(fc, "cgroup1: noprefix used incorrectly");
>  
>  	/* Can't specify "none" and some subsystems */
> -	if (opts->subsys_mask && opts->none)
> -		return -EINVAL;
> +	if (ctx->subsys_mask && ctx->none)
> +		return cg_invalf(fc, "cgroup1: none used incorrectly");
>  
>  	return 0;
>  }
>  
> -static int cgroup1_remount(struct kernfs_root *kf_root, int *flags, char *data)
> +static int cgroup1_reconfigure(struct kernfs_root *kf_root, struct fs_context *fc)
>  {
> -	int ret = 0;
> +	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
>  	struct cgroup_root *root = cgroup_root_from_kf(kf_root);
> -	struct cgroup_sb_opts opts;
>  	u16 added_mask, removed_mask;
> +	int ret = 0;
>  
>  	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
>  
> -	/* See what subsystems are wanted */
> -	ret = parse_cgroupfs_options(data, &opts);
> -	if (ret)
> -		goto out_unlock;
> -
> -	if (opts.subsys_mask != root->subsys_mask || opts.release_agent)
> +	if (ctx->subsys_mask != root->subsys_mask || ctx->release_agent)
>  		pr_warn("option changes via remount are deprecated (pid=%d comm=%s)\n",
>  			task_tgid_nr(current), current->comm);
>  
> -	added_mask = opts.subsys_mask & ~root->subsys_mask;
> -	removed_mask = root->subsys_mask & ~opts.subsys_mask;
> +	added_mask = ctx->subsys_mask & ~root->subsys_mask;
> +	removed_mask = root->subsys_mask & ~ctx->subsys_mask;
>  
>  	/* Don't allow flags or name to change at remount */
> -	if ((opts.flags ^ root->flags) ||
> -	    (opts.name && strcmp(opts.name, root->name))) {
> -		pr_err("option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"\n",
> -		       opts.flags, opts.name ?: "", root->flags, root->name);
> +	if ((ctx->flags ^ root->flags) ||
> +	    (ctx->name && strcmp(ctx->name, root->name))) {
> +		cg_invalf(fc, "option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"",
> +		       ctx->flags, ctx->name ?: "", root->flags, root->name);
>  		ret = -EINVAL;
>  		goto out_unlock;
>  	}
> @@ -1081,17 +1122,15 @@ static int cgroup1_remount(struct kernfs_root *kf_root, int *flags, char *data)
>  
>  	WARN_ON(rebind_subsystems(&cgrp_dfl_root, removed_mask));
>  
> -	if (opts.release_agent) {
> +	if (ctx->release_agent) {
>  		spin_lock(&release_agent_path_lock);
> -		strcpy(root->release_agent_path, opts.release_agent);
> +		strcpy(root->release_agent_path, ctx->release_agent);
>  		spin_unlock(&release_agent_path_lock);
>  	}
>  
>  	trace_cgroup_remount(root);
>  
>   out_unlock:
> -	kfree(opts.release_agent);
> -	kfree(opts.name);
>  	mutex_unlock(&cgroup_mutex);
>  	return ret;
>  }
> @@ -1099,31 +1138,26 @@ static int cgroup1_remount(struct kernfs_root *kf_root, int *flags, char *data)
>  struct kernfs_syscall_ops cgroup1_kf_syscall_ops = {
>  	.rename			= cgroup1_rename,
>  	.show_options		= cgroup1_show_options,
> -	.remount_fs		= cgroup1_remount,
> +	.reconfigure		= cgroup1_reconfigure,
>  	.mkdir			= cgroup_mkdir,
>  	.rmdir			= cgroup_rmdir,
>  	.show_path		= cgroup_show_path,
>  };
>  
> -struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
> -			     void *data, unsigned long magic,
> -			     struct cgroup_namespace *ns)
> +/*
> + * Find or create a v1 cgroups superblock.
> + */
> +int cgroup1_get_tree(struct fs_context *fc)
>  {
> +	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
>  	struct super_block *pinned_sb = NULL;
> -	struct cgroup_sb_opts opts;
>  	struct cgroup_root *root;
>  	struct cgroup_subsys *ss;
> -	struct dentry *dentry;
>  	int i, ret;
>  	bool new_root = false;
>  
>  	cgroup_lock_and_drain_offline(&cgrp_dfl_root.cgrp);
>  
> -	/* First find the desired set of subsystems */
> -	ret = parse_cgroupfs_options(data, &opts);
> -	if (ret)
> -		goto out_unlock;
> -
>  	/*
>  	 * Destruction of cgroup root is asynchronous, so subsystems may
>  	 * still be dying after the previous unmount.  Let's drain the
> @@ -1132,15 +1166,13 @@ struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
>  	 * starting.  Testing ref liveliness is good enough.
>  	 */
>  	for_each_subsys(ss, i) {
> -		if (!(opts.subsys_mask & (1 << i)) ||
> +		if (!(ctx->subsys_mask & (1 << i)) ||
>  		    ss->root == &cgrp_dfl_root)
>  			continue;
>  
>  		if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) {
>  			mutex_unlock(&cgroup_mutex);
> -			msleep(10);
> -			ret = restart_syscall();
> -			goto out_free;
> +			goto err_restart;
>  		}
>  		cgroup_put(&ss->root->cgrp);
>  	}
> @@ -1156,8 +1188,8 @@ struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
>  		 * name matches but sybsys_mask doesn't, we should fail.
>  		 * Remember whether name matched.
>  		 */
> -		if (opts.name) {
> -			if (strcmp(opts.name, root->name))
> +		if (ctx->name) {
> +			if (strcmp(ctx->name, root->name))
>  				continue;
>  			name_match = true;
>  		}
> @@ -1166,15 +1198,15 @@ struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
>  		 * If we asked for subsystems (or explicitly for no
>  		 * subsystems) then they must match.
>  		 */
> -		if ((opts.subsys_mask || opts.none) &&
> -		    (opts.subsys_mask != root->subsys_mask)) {
> +		if ((ctx->subsys_mask || ctx->none) &&
> +		    (ctx->subsys_mask != root->subsys_mask)) {
>  			if (!name_match)
>  				continue;
>  			ret = -EBUSY;
> -			goto out_unlock;
> +			goto err_unlock;
>  		}
>  
> -		if (root->flags ^ opts.flags)
> +		if (root->flags ^ ctx->flags)
>  			pr_warn("new mount options do not match the existing superblock, will be ignored\n");
>  
>  		/*
> @@ -1195,11 +1227,10 @@ struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
>  			mutex_unlock(&cgroup_mutex);
>  			if (!IS_ERR_OR_NULL(pinned_sb))
>  				deactivate_super(pinned_sb);
> -			msleep(10);
> -			ret = restart_syscall();
> -			goto out_free;
> +			goto err_restart;
>  		}
>  
> +		ctx->root = root;
>  		ret = 0;
>  		goto out_unlock;
>  	}
> @@ -1209,41 +1240,35 @@ struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
>  	 * specification is allowed for already existing hierarchies but we
>  	 * can't create new one without subsys specification.
>  	 */
> -	if (!opts.subsys_mask && !opts.none) {
> -		ret = -EINVAL;
> -		goto out_unlock;
> +	if (!ctx->subsys_mask && !ctx->none) {
> +		ret = cg_invalf(fc, "cgroup1: No subsys list or none specified");
> +		goto err_unlock;
>  	}
>  
>  	/* Hierarchies may only be created in the initial cgroup namespace. */
> -	if (ns != &init_cgroup_ns) {
> +	if (ctx->ns != &init_cgroup_ns) {
>  		ret = -EPERM;
> -		goto out_unlock;
> +		goto err_unlock;
>  	}
>  
>  	root = kzalloc(sizeof(*root), GFP_KERNEL);
>  	if (!root) {
>  		ret = -ENOMEM;
> -		goto out_unlock;
> +		goto err_unlock;
>  	}
>  	new_root = true;
> +	ctx->root = root;
>  
> -	init_cgroup_root(root, &opts);
> +	init_cgroup_root(ctx);
>  
> -	ret = cgroup_setup_root(root, opts.subsys_mask, PERCPU_REF_INIT_DEAD);
> +	ret = cgroup_setup_root(root, ctx->subsys_mask, PERCPU_REF_INIT_DEAD);
>  	if (ret)
> -		cgroup_free_root(root);
> +		goto err_unlock;
>  
>  out_unlock:
>  	mutex_unlock(&cgroup_mutex);
> -out_free:
> -	kfree(opts.release_agent);
> -	kfree(opts.name);
> -
> -	if (ret)
> -		return ERR_PTR(ret);
>  
> -	dentry = cgroup_do_mount(&cgroup_fs_type, flags, root,
> -				 CGROUP_SUPER_MAGIC, ns);
> +	ret = cgroup_do_get_tree(fc);
>  
>  	/*
>  	 * There's a race window after we release cgroup_mutex and before
> @@ -1256,6 +1281,7 @@ struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
>  		percpu_ref_reinit(&root->cgrp.self.refcnt);
>  		mutex_unlock(&cgroup_mutex);
>  	}
> +	cgroup_get(&root->cgrp);
>  
>  	/*
>  	 * If @pinned_sb, we're reusing an existing root and holding an
> @@ -1264,7 +1290,14 @@ struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags,
>  	if (pinned_sb)
>  		deactivate_super(pinned_sb);
>  
> -	return dentry;
> +	return ret;
> +
> +err_restart:
> +	msleep(10);
> +	return restart_syscall();
> +err_unlock:
> +	mutex_unlock(&cgroup_mutex);
> +	return ret;
>  }
>  
>  static int __init cgroup1_wq_init(void)
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 48dbf249bec5..3c3c40cad257 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -54,6 +54,7 @@
>  #include <linux/proc_ns.h>
>  #include <linux/nsproxy.h>
>  #include <linux/file.h>
> +#include <linux/fs_parser.h>
>  #include <linux/sched/cputime.h>
>  #include <net/sock.h>
>  
> @@ -1737,25 +1738,51 @@ int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
>  	return len;
>  }
>  
> -static int parse_cgroup_root_flags(char *data, unsigned int *root_flags)
> -{
> -	char *token;
> +enum cgroup2_param {
> +	Opt_nsdelegate,
> +	nr__cgroup2_params
> +};
>  
> -	*root_flags = 0;
> +static const struct fs_parameter_spec cgroup2_param_specs[nr__cgroup2_params] = {
> +	[Opt_nsdelegate]	= { fs_param_is_flag },
> +};
>  
> -	if (!data)
> -		return 0;
> +static const char *const cgroup2_param_keys[nr__cgroup2_params] = {
> +	[Opt_nsdelegate]	= "nsdelegate",
> +};
>  
> -	while ((token = strsep(&data, ",")) != NULL) {
> -		if (!strcmp(token, "nsdelegate")) {
> -			*root_flags |= CGRP_ROOT_NS_DELEGATE;
> -			continue;
> -		}
> +static const struct fs_parameter_description cgroup2_fs_parameters = {
> +	.name		= "cgroup2",
> +	.nr_params	= nr__cgroup2_params,
> +	.keys		= cgroup2_param_keys,
> +	.specs		= cgroup2_param_specs,
> +	.no_source	= true,
> +};
>  
> -		pr_err("cgroup2: unknown option \"%s\"\n", token);
> -		return -EINVAL;
> +static int cgroup2_parse_param(struct fs_context *fc, struct fs_parameter *param)
> +{
> +	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
> +	struct fs_parse_result result;
> +	int opt;
> +
> +	opt = fs_parse(fc, &cgroup2_fs_parameters, param, &result);
> +	if (opt < 0)
> +		return opt;
> +
> +	switch (opt) {
> +	case Opt_nsdelegate:
> +		ctx->flags |= CGRP_ROOT_NS_DELEGATE;
> +		return 0;
>  	}
>  
> +	return -EINVAL;
> +}
> +
> +static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
> +{
> +	if (current->nsproxy->cgroup_ns == &init_cgroup_ns &&
> +	    cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE)
> +		seq_puts(seq, ",nsdelegate");
>  	return 0;
>  }
>  
> @@ -1769,23 +1796,11 @@ static void apply_cgroup_root_flags(unsigned int root_flags)
>  	}
>  }
>  
> -static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root)
> -{
> -	if (cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE)
> -		seq_puts(seq, ",nsdelegate");
> -	return 0;
> -}
> -
> -static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
> +static int cgroup_reconfigure(struct kernfs_root *kf_root, struct fs_context *fc)
>  {
> -	unsigned int root_flags;
> -	int ret;
> +	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
>  
> -	ret = parse_cgroup_root_flags(data, &root_flags);
> -	if (ret)
> -		return ret;
> -
> -	apply_cgroup_root_flags(root_flags);
> +	apply_cgroup_root_flags(ctx->flags);
>  	return 0;
>  }
>  
> @@ -1873,8 +1888,9 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
>  	INIT_WORK(&cgrp->release_agent_work, cgroup1_release_agent);
>  }
>  
> -void init_cgroup_root(struct cgroup_root *root, struct cgroup_sb_opts *opts)
> +void init_cgroup_root(struct cgroup_fs_context *ctx)
>  {
> +	struct cgroup_root *root = ctx->root;
>  	struct cgroup *cgrp = &root->cgrp;
>  
>  	INIT_LIST_HEAD(&root->root_list);
> @@ -1883,12 +1899,12 @@ void init_cgroup_root(struct cgroup_root *root, struct cgroup_sb_opts *opts)
>  	init_cgroup_housekeeping(cgrp);
>  	idr_init(&root->cgroup_idr);
>  
> -	root->flags = opts->flags;
> -	if (opts->release_agent)
> -		strscpy(root->release_agent_path, opts->release_agent, PATH_MAX);
> -	if (opts->name)
> -		strscpy(root->name, opts->name, MAX_CGROUP_ROOT_NAMELEN);
> -	if (opts->cpuset_clone_children)
> +	root->flags = ctx->flags;
> +	if (ctx->release_agent)
> +		strscpy(root->release_agent_path, ctx->release_agent, PATH_MAX);
> +	if (ctx->name)
> +		strscpy(root->name, ctx->name, MAX_CGROUP_ROOT_NAMELEN);
> +	if (ctx->cpuset_clone_children)
>  		set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags);
>  }
>  
> @@ -1993,57 +2009,53 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask, int ref_flags)
>  	return ret;
>  }
>  
> -struct dentry *cgroup_do_mount(struct file_system_type *fs_type, int flags,
> -			       struct cgroup_root *root, unsigned long magic,
> -			       struct cgroup_namespace *ns)
> +int cgroup_do_get_tree(struct fs_context *fc)
>  {
> -	struct dentry *dentry;
> -	bool new_sb;
> +	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
> +	int ret;
>  
> -	dentry = kernfs_mount(fs_type, flags, root->kf_root, magic, &new_sb);
> +	ctx->kfc.root = ctx->root->kf_root;
> +
> +	ret = kernfs_get_tree(fc);
> +	if (ret < 0)
> +		goto out_cgrp;
>  
>  	/*
>  	 * In non-init cgroup namespace, instead of root cgroup's dentry,
>  	 * we return the dentry corresponding to the cgroupns->root_cgrp.
>  	 */
> -	if (!IS_ERR(dentry) && ns != &init_cgroup_ns) {
> +	if (ctx->ns != &init_cgroup_ns) {
>  		struct dentry *nsdentry;
>  		struct cgroup *cgrp;
>  
>  		mutex_lock(&cgroup_mutex);
>  		spin_lock_irq(&css_set_lock);
>  
> -		cgrp = cset_cgroup_from_root(ns->root_cset, root);
> +		cgrp = cset_cgroup_from_root(ctx->ns->root_cset, ctx->root);
>  
>  		spin_unlock_irq(&css_set_lock);
>  		mutex_unlock(&cgroup_mutex);
>  
> -		nsdentry = kernfs_node_dentry(cgrp->kn, dentry->d_sb);
> -		dput(dentry);
> -		dentry = nsdentry;
> +		nsdentry = kernfs_node_dentry(cgrp->kn, fc->root->d_sb);
> +		if (IS_ERR(nsdentry))
> +			return PTR_ERR(nsdentry);
> +		dput(fc->root);
> +		fc->root = nsdentry;
>  	}
>  
> -	if (IS_ERR(dentry) || !new_sb)
> -		cgroup_put(&root->cgrp);

I don't see where this cgroup_put() has been moved.

With this patch, the next script works only once, on the second attempt
it hangs up on mounting a cgroup file system.

This is the only suspicious place in this patch what I have found.

[root@fc24 ~]# cat fs-vs-cg 
d=$(mktemp -d /tmp/cg.XXXXXX)
mkdir $d/a
mkdir $d/b
mount -t cgroup -o none,name=xxxx xxx $d/a
mount -t cgroup -o none,name=xxxx xxx $d/b
umount $d/a
umount $d/b

[root@fc24 ~]# unshare -m --propagation private bash -x fs-vs-cg
++ mktemp -d /tmp/cg.XXXXXX
+ d=/tmp/cg.yUfagS
+ mkdir /tmp/cg.yUfagS/a
+ mkdir /tmp/cg.yUfagS/b
+ mount -t cgroup -o none,name=xxxx xxx /tmp/cg.yUfagS/a
+ mount -t cgroup -o none,name=xxxx xxx /tmp/cg.yUfagS/b
+ umount /tmp/cg.yUfagS/a
+ umount /tmp/cg.yUfagS/b
[root@fc24 ~]# unshare -m --propagation private bash -x fs-vs-cg
++ mktemp -d /tmp/cg.XXXXXX
+ d=/tmp/cg.ippWUn
+ mkdir /tmp/cg.ippWUn/a
+ mkdir /tmp/cg.ippWUn/b
+ mount -t cgroup -o none,name=xxxx xxx /tmp/cg.ippWUn/a
^Z
[1]+  Stopped                 unshare -m --propagation private bash -x fs-vs-cg

[root@fc24 ~]# ps
  PID TTY          TIME CMD
  556 pts/0    00:00:00 bash
  591 pts/0    00:00:00 bash
  595 pts/0    00:00:00 mount
  596 pts/0    00:00:00 ps

[root@fc24 ~]# bg
[1]+ unshare -m --propagation private bash -x fs-vs-cg &

[root@fc24 ~]# cat /proc/595/stack 
[<0>] msleep+0x38/0x40
[<0>] cgroup1_get_tree+0x4e1/0x72c
[<0>] vfs_get_tree+0x5e/0x140
[<0>] do_mount+0x326/0xc70
[<0>] ksys_mount+0xba/0xd0
[<0>] __x64_sys_mount+0x21/0x30
[<0>] do_syscall_64+0x60/0x210
[<0>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[<0>] 0xffffffffffffffff

> +	ret = 0;
> +	if (ctx->kfc.new_sb_created)
> +		goto out_cgrp;
> +	apply_cgroup_root_flags(ctx->flags);
> +	return 0;
>  
> -	return dentry;
> +out_cgrp:
> +	return ret;
>  }
>  
> -static struct dentry *cgroup_mount(struct file_system_type *fs_type,
> -			 int flags, const char *unused_dev_name,
> -			 void *data, size_t data_size)
> +static int cgroup_get_tree(struct fs_context *fc)
>  {
> -	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
> -	struct dentry *dentry;
> -	int ret;
> -
> -	get_cgroup_ns(ns);
> -
> -	/* Check if the caller has permission to mount. */
> -	if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) {
> -		put_cgroup_ns(ns);
> -		return ERR_PTR(-EPERM);
> -	}
> +	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
>  
>  	/*
>  	 * The first time anyone tries to mount a cgroup, enable the list
> @@ -2052,29 +2064,96 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
>  	if (!use_task_css_set_links)
>  		cgroup_enable_task_cg_lists();
>  
> -	if (fs_type == &cgroup2_fs_type) {
> -		unsigned int root_flags;
> -
> -		ret = parse_cgroup_root_flags(data, &root_flags);
> -		if (ret) {
> -			put_cgroup_ns(ns);
> -			return ERR_PTR(ret);
> -		}
> +	switch (ctx->version) {
> +	case 1:
> +		return cgroup1_get_tree(fc);
>  
> +	case 2:
>  		cgrp_dfl_visible = true;
>  		cgroup_get_live(&cgrp_dfl_root.cgrp);
>  
> -		dentry = cgroup_do_mount(&cgroup2_fs_type, flags, &cgrp_dfl_root,
> -					 CGROUP2_SUPER_MAGIC, ns);
> -		if (!IS_ERR(dentry))
> -			apply_cgroup_root_flags(root_flags);
> -	} else {
> -		dentry = cgroup1_mount(&cgroup_fs_type, flags, data,
> -				       CGROUP_SUPER_MAGIC, ns);
> +		ctx->root = &cgrp_dfl_root;
> +		return cgroup_do_get_tree(fc);
> +
> +	default:
> +		BUG();
> +	}
> +}
> +
> +static int cgroup_parse_param(struct fs_context *fc, struct fs_parameter *param)
> +{
> +	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
> +
> +	if (ctx->version == 1)
> +		return cgroup1_parse_param(fc, param);
> +
> +	return cgroup2_parse_param(fc, param);
> +}
> +
> +static int cgroup_validate(struct fs_context *fc)
> +{
> +	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
> +
> +	if (ctx->version == 1)
> +		return cgroup1_validate(fc);
> +	return 0;
> +}
> +
> +/*
> + * Destroy a cgroup filesystem context.
> + */
> +static void cgroup_fs_context_free(struct fs_context *fc)
> +{
> +	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
> +
> +	kfree(ctx->name);
> +	kfree(ctx->release_agent);
> +	if (ctx->root)
> +		cgroup_put(&ctx->root->cgrp);
> +	put_cgroup_ns(ctx->ns);
> +	kernfs_free_fs_context(fc);
> +	kfree(ctx);
> +}
> +
> +static const struct fs_context_operations cgroup_fs_context_ops = {
> +	.free		= cgroup_fs_context_free,
> +	.parse_param	= cgroup_parse_param,
> +	.validate	= cgroup_validate,
> +	.get_tree	= cgroup_get_tree,
> +	.reconfigure	= kernfs_reconfigure,
> +};
> +
> +/*
> + * Initialise the cgroup filesystem creation/reconfiguration context.  Notably,
> + * we select the namespace we're going to use.
> + */
> +static int cgroup_init_fs_context(struct fs_context *fc, struct dentry *reference)
> +{
> +	struct cgroup_fs_context *ctx;
> +	struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
> +
> +	switch (fc->purpose) {
> +	case FS_CONTEXT_FOR_UMOUNT:
> +	case FS_CONTEXT_FOR_EMERGENCY_RO:
> +		return -EOPNOTSUPP;
> +	default:
> +		break;
>  	}
>  
> -	put_cgroup_ns(ns);
> -	return dentry;
> +	/* Check if the caller has permission to mount. */
> +	if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
> +		return -EPERM;
> +
> +	ctx = kzalloc(sizeof(struct cgroup_fs_context), GFP_KERNEL);
> +	if (!ctx)
> +		return -ENOMEM;
> +
> +	ctx->ns = get_cgroup_ns(ns);
> +	ctx->version = (fc->fs_type == &cgroup2_fs_type) ? 2 : 1;
> +	ctx->kfc.magic = (ctx->version == 2) ? CGROUP2_SUPER_MAGIC : CGROUP_SUPER_MAGIC;
> +	fc->fs_private = &ctx->kfc;
> +	fc->ops = &cgroup_fs_context_ops;
> +	return 0;
>  }
>  
>  static void cgroup_kill_sb(struct super_block *sb)
> @@ -2099,17 +2178,19 @@ static void cgroup_kill_sb(struct super_block *sb)
>  }
>  
>  struct file_system_type cgroup_fs_type = {
> -	.name = "cgroup",
> -	.mount = cgroup_mount,
> -	.kill_sb = cgroup_kill_sb,
> -	.fs_flags = FS_USERNS_MOUNT,
> +	.name			= "cgroup",
> +	.init_fs_context	= cgroup_init_fs_context,
> +	.parameters		= &cgroup1_fs_parameters,
> +	.kill_sb		= cgroup_kill_sb,
> +	.fs_flags		= FS_USERNS_MOUNT,
>  };
>  
>  static struct file_system_type cgroup2_fs_type = {
> -	.name = "cgroup2",
> -	.mount = cgroup_mount,
> -	.kill_sb = cgroup_kill_sb,
> -	.fs_flags = FS_USERNS_MOUNT,
> +	.name			= "cgroup2",
> +	.init_fs_context	= cgroup_init_fs_context,
> +	.parameters		= &cgroup2_fs_parameters,
> +	.kill_sb		= cgroup_kill_sb,
> +	.fs_flags		= FS_USERNS_MOUNT,
>  };
>  
>  int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
> @@ -5179,7 +5260,7 @@ int cgroup_rmdir(struct kernfs_node *kn)
>  
>  static struct kernfs_syscall_ops cgroup_kf_syscall_ops = {
>  	.show_options		= cgroup_show_options,
> -	.remount_fs		= cgroup_remount,
> +	.reconfigure		= cgroup_reconfigure,
>  	.mkdir			= cgroup_mkdir,
>  	.rmdir			= cgroup_rmdir,
>  	.show_path		= cgroup_show_path,
> @@ -5246,11 +5327,12 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
>   */
>  int __init cgroup_init_early(void)
>  {
> -	static struct cgroup_sb_opts __initdata opts;
> +	static struct cgroup_fs_context __initdata ctx;
>  	struct cgroup_subsys *ss;
>  	int i;
>  
> -	init_cgroup_root(&cgrp_dfl_root, &opts);
> +	ctx.root = &cgrp_dfl_root;
> +	init_cgroup_root(&ctx);
>  	cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
>  
>  	RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index df78e166028c..b4ad1a52f006 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -324,10 +324,8 @@ static int cpuset_get_tree(struct fs_context *fc)
>  	int ret = -ENODEV;
>  
>  	cgroup_fs = get_fs_type("cgroup");
> -	if (cgroup_fs) {
> -		ret = PTR_ERR(cgroup_fs);
> +	if (!cgroup_fs)
>  		goto out;
> -	}
>  
>  	cg_fc = vfs_new_fs_context(cgroup_fs, NULL, fc->sb_flags, fc->sb_flags,
>  				   fc->purpose);