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Commit 05ef1d7c authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: introduce struct cfent 



This patch adds cfent (cgroup file entry) which is the association
between a cgroup and a file.  This is in-cgroup representation of
files under a cgroup directory.  This simplifies walking walking
cgroup files and thus cgroup_clear_directory(), which is now
implemented in two parts - cgroup_rm_file() and a loop around it.

cgroup_rm_file() will be used to implement cftype removal and cfent is
scheduled to serve cgroup specific per-file data (e.g. for sysfs-like
"sever" semantics).

v2: - cfe was freed from cgroup_rm_file() which led to use-after-free
      if the file had openers at the time of removal.  Moved to
      cgroup_diput().

    - cgroup_clear_directory() triggered WARN_ON_ONCE() if d_subdirs
      wasn't empty after removing all files.  This triggered
      spuriously if some files were open during directory clearing.
      Removed.

v3: - In cgroup_diput(), WARN_ONCE(!list_empty(&cfe->node)) could be
      spuriously triggered for root cgroups because they don't go
      through cgroup_clear_directory() on unmount.  Don't trigger WARN
      for root cgroups.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
Cc: Glauber Costa <glommer@parallels.com>
parent f6ea9372

include/linux/cgroup.h

+1 −0
Original line number Diff line number Diff line
@@ -175,6 +175,7 @@ struct cgroup { 
	 */

	struct list_head sibling;	/* my parent's children */

	struct list_head children;	/* my children */

	struct list_head files;		/* my files */



	struct cgroup *parent;		/* my parent */

	struct dentry __rcu *dentry;	/* cgroup fs entry, RCU protected */

kernel/cgroup.c

+77 −36
Original line number Diff line number Diff line
@@ -147,6 +147,15 @@ struct cgroupfs_root { 
 */

static struct cgroupfs_root rootnode;



/*

 * cgroupfs file entry, pointed to from leaf dentry->d_fsdata.

 */

struct cfent {

	struct list_head		node;

	struct dentry			*dentry;

	struct cftype			*type;

};



/*

 * CSS ID -- ID per subsys's Cgroup Subsys State(CSS). used only when

 * cgroup_subsys->use_id != 0.
@@ -287,11 +296,16 @@ static inline struct cgroup *__d_cgrp(struct dentry *dentry) 
	return dentry->d_fsdata;

}



static inline struct cftype *__d_cft(struct dentry *dentry)

static inline struct cfent *__d_cfe(struct dentry *dentry)

{

	return dentry->d_fsdata;

}



static inline struct cftype *__d_cft(struct dentry *dentry)

{

	return __d_cfe(dentry)->type;

}



/* the list of cgroups eligible for automatic release. Protected by

 * release_list_lock */

static LIST_HEAD(release_list);
@@ -877,6 +891,14 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode) 
		BUG_ON(!list_empty(&cgrp->pidlists));



		kfree_rcu(cgrp, rcu_head);

	} else {

		struct cfent *cfe = __d_cfe(dentry);

		struct cgroup *cgrp = dentry->d_parent->d_fsdata;



		WARN_ONCE(!list_empty(&cfe->node) &&

			  cgrp != &cgrp->root->top_cgroup,

			  "cfe still linked for %s\n", cfe->type->name);

		kfree(cfe);

	}

	iput(inode);

}
@@ -895,34 +917,36 @@ static void remove_dir(struct dentry *d) 
	dput(parent);

}



static void cgroup_clear_directory(struct dentry *dentry)

static int cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)

{

	struct list_head *node;

	struct cfent *cfe;



	BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));

	spin_lock(&dentry->d_lock);

	node = dentry->d_subdirs.next;

	while (node != &dentry->d_subdirs) {

		struct dentry *d = list_entry(node, struct dentry, d_u.d_child);

	lockdep_assert_held(&cgrp->dentry->d_inode->i_mutex);

	lockdep_assert_held(&cgroup_mutex);



		spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);

		list_del_init(node);

		if (d->d_inode) {

			/* This should never be called on a cgroup

			 * directory with child cgroups */

			BUG_ON(d->d_inode->i_mode & S_IFDIR);

			dget_dlock(d);

			spin_unlock(&d->d_lock);

			spin_unlock(&dentry->d_lock);

	list_for_each_entry(cfe, &cgrp->files, node) {

		struct dentry *d = cfe->dentry;



		if (cft && cfe->type != cft)

			continue;



		dget(d);

		d_delete(d);

			simple_unlink(dentry->d_inode, d);

		simple_unlink(d->d_inode, d);

		list_del_init(&cfe->node);

		dput(d);

			spin_lock(&dentry->d_lock);

		} else

			spin_unlock(&d->d_lock);

		node = dentry->d_subdirs.next;



		return 0;

	}

	spin_unlock(&dentry->d_lock);

	return -ENOENT;

}



static void cgroup_clear_directory(struct dentry *dir)

{

	struct cgroup *cgrp = __d_cgrp(dir);



	while (!list_empty(&cgrp->files))

		cgroup_rm_file(cgrp, NULL);

}



/*
@@ -1352,6 +1376,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp) 
{

	INIT_LIST_HEAD(&cgrp->sibling);

	INIT_LIST_HEAD(&cgrp->children);

	INIT_LIST_HEAD(&cgrp->files);

	INIT_LIST_HEAD(&cgrp->css_sets);

	INIT_LIST_HEAD(&cgrp->release_list);

	INIT_LIST_HEAD(&cgrp->pidlists);
@@ -2619,7 +2644,9 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys, 
			   const struct cftype *cft)

{

	struct dentry *dir = cgrp->dentry;

	struct cgroup *parent = __d_cgrp(dir);

	struct dentry *dentry;

	struct cfent *cfe;

	int error;

	umode_t mode;

	char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
@@ -2635,17 +2662,31 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys, 
		strcat(name, ".");

	}

	strcat(name, cft->name);



	BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));



	cfe = kzalloc(sizeof(*cfe), GFP_KERNEL);

	if (!cfe)

		return -ENOMEM;



	dentry = lookup_one_len(name, dir, strlen(name));

	if (!IS_ERR(dentry)) {

	if (IS_ERR(dentry)) {

		error = PTR_ERR(dentry);

		goto out;

	}



	mode = cgroup_file_mode(cft);

		error = cgroup_create_file(dentry, mode | S_IFREG,

						cgrp->root->sb);

		if (!error)

			dentry->d_fsdata = (void *)cft;

	error = cgroup_create_file(dentry, mode | S_IFREG, cgrp->root->sb);

	if (!error) {

		cfe->type = (void *)cft;

		cfe->dentry = dentry;

		dentry->d_fsdata = cfe;

		list_add_tail(&cfe->node, &parent->files);

		cfe = NULL;

	}

	dput(dentry);

	} else

		error = PTR_ERR(dentry);

out:

	kfree(cfe);

	return error;

}