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>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 66a416b..163c890 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -763,6 +763,8 @@
* -> 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 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 @@
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 @@
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;