> @@ -1291,6 +1324,7 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
> struct cgroupfs_root *new_root;
>
> /* First find the desired set of subsystems */
> + down_read(&subsys_mutex);
Hmm.. this can lead to deadlock. sget() returns success with sb->s_umount
held, so here we have:
down_read(&subsys_mutex);
down_write(&sb->s_umount);
On the other hand, sb->s_umount is held before calling kill_sb(),
so when umounting we have:
down_write(&sb->s_umount);
down_read(&subsys_mutex);
> ret = parse_cgroupfs_options(data, &opts);
> if (ret)
> goto out_err;
> @@ -1367,6 +1401,8 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
> free_cg_links(&tmp_cg_links);
> goto drop_new_super;
> }
> + /* done with subsys stuff and no other failure case */
> + up_read(&subsys_mutex);
>
> /* EBUSY should be the only error here */
> BUG_ON(ret);
> @@ -1415,6 +1451,7 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
> drop_new_super:
> deactivate_locked_super(sb);
> out_err:
> + up_read(&subsys_mutex);
> kfree(opts.release_agent);
> kfree(opts.name);
>
> @@ -1434,10 +1471,12 @@ static void cgroup_kill_sb(struct super_block *sb) {
> BUG_ON(!list_empty(&cgrp->children));
> BUG_ON(!list_empty(&cgrp->sibling));
>
> + down_read(&subsys_mutex);
> mutex_lock(&cgroup_mutex);
>
> /* Rebind all subsystems back to the default hierarchy */
> ret = rebind_subsystems(root, 0);
> + up_read(&subsys_mutex);
> /* Shouldn't be able to fail ... */
> BUG_ON(ret);
>
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