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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: Nick Piggin <npiggin@kernel.dk>
This commit is contained in:
Nick Piggin 2011-01-07 17:49:20 +11:00
parent 3e880fb5e4
commit 5adcee1d8d
1 changed files with 22 additions and 5 deletions
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27
kernel/cgroup.c
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@ -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)
{
static const struct dentry_operations cgroup_dops = {
return 1;
}
static struct dentry *cgroup_lookup(struct inode *dir,
struct dentry *dentry, struct nameidata *nd)
{
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;