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Commit 5adcee1d authored by Nick Piggin's avatar Nick Piggin
Browse files

cgroup fs: avoid switching ->d_op on live dentry 



Switching d_op on a live dentry is racy in general, so avoid it. In this case
it is a negative dentry, which is safer, but there are still concurrent ops
which may be called on d_op in that case (eg. d_revalidate). So in general
a filesystem may not do this. Fix cgroupfs so as not to do this.

Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
parent 3e880fb5

kernel/cgroup.c

+22 −5
Original line number Diff line number Diff line
@@ -763,6 +763,8 @@ EXPORT_SYMBOL_GPL(cgroup_unlock); 
 * -> cgroup_mkdir.

 */



static struct dentry *cgroup_lookup(struct inode *dir,

			struct dentry *dentry, struct nameidata *nd);

static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode);

static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);

static int cgroup_populate_dir(struct cgroup *cgrp);
@@ -2180,7 +2182,7 @@ static const struct file_operations cgroup_file_operations = { 
};



static const struct inode_operations cgroup_dir_inode_operations = {

	.lookup = simple_lookup,

	.lookup = cgroup_lookup,

	.mkdir = cgroup_mkdir,

	.rmdir = cgroup_rmdir,

	.rename = cgroup_rename,
@@ -2196,13 +2198,29 @@ static inline struct cftype *__file_cft(struct file *file) 
	return __d_cft(file->f_dentry);

}



static int cgroup_create_file(struct dentry *dentry, mode_t mode,

				struct super_block *sb)

static int cgroup_delete_dentry(struct dentry *dentry)

{

	return 1;

}



static struct dentry *cgroup_lookup(struct inode *dir,

			struct dentry *dentry, struct nameidata *nd)

{

	static const struct dentry_operations cgroup_dops = {

	static const struct dentry_operations cgroup_dentry_operations = {

		.d_delete = cgroup_delete_dentry,

		.d_iput = cgroup_diput,

	};



	if (dentry->d_name.len > NAME_MAX)

		return ERR_PTR(-ENAMETOOLONG);

	dentry->d_op = &cgroup_dentry_operations;

	d_add(dentry, NULL);

	return NULL;

}



static int cgroup_create_file(struct dentry *dentry, mode_t mode,

				struct super_block *sb)

{

	struct inode *inode;



	if (!dentry)
@@ -2228,7 +2246,6 @@ static int cgroup_create_file(struct dentry *dentry, mode_t mode, 
		inode->i_size = 0;

		inode->i_fop = &cgroup_file_operations;

	}

	dentry->d_op = &cgroup_dops;

	d_instantiate(dentry, inode);

	dget(dentry);	/* Extra count - pin the dentry in core */

	return 0;