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Commit e756c7b6 authored by Zefan Li's avatar Zefan Li Committed by Tejun Heo
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Revert "cgroup: remove redundant variable in cgroup_mount()" 



This reverts commit 0c7bf3e8.

If there are child cgroups in the cgroupfs and then we umount it,
the superblock will be destroyed but the cgroup_root will be kept
around. When we mount it again, cgroup_mount() will find this
cgroup_root and allocate a new sb for it.

So with this commit we will be trapped in a dead loop in the case
described above, because kernfs_pin_sb() keeps returning NULL.

Currently I don't see how we can avoid using both pinned_sb and
new_sb, so just revert it.

Cc: Al Viro <viro@ZenIV.linux.org.uk>
Reported-by: default avatarAndrey Wagin <avagin@gmail.com>
Signed-off-by: default avatarZefan Li <lizefan@huawei.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 0c7bf3e8

kernel/cgroup.c

+7 −4
Original line number Diff line number Diff line
@@ -1694,6 +1694,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, 
	struct dentry *dentry;

	int ret;

	int i;

	bool new_sb;



	/*

	 * The first time anyone tries to mount a cgroup, enable the list
@@ -1784,7 +1785,7 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, 
		 * path is super cold.  Let's just sleep a bit and retry.

		 */

		pinned_sb = kernfs_pin_sb(root->kf_root, NULL);

		if (IS_ERR_OR_NULL(pinned_sb) ||

		if (IS_ERR(pinned_sb) ||

		    !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) {

			mutex_unlock(&cgroup_mutex);

			if (!IS_ERR_OR_NULL(pinned_sb))
@@ -1830,16 +1831,18 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, 
		return ERR_PTR(ret);



	dentry = kernfs_mount(fs_type, flags, root->kf_root,

				CGROUP_SUPER_MAGIC, NULL);

	if (IS_ERR(dentry) || pinned_sb)

				CGROUP_SUPER_MAGIC, &new_sb);

	if (IS_ERR(dentry) || !new_sb)

		cgroup_put(&root->cgrp);



	/*

	 * If @pinned_sb, we're reusing an existing root and holding an

	 * extra ref on its sb.  Mount is complete.  Put the extra ref.

	 */

	if (pinned_sb)

	if (pinned_sb) {

		WARN_ON(new_sb);

		deactivate_super(pinned_sb);

	}



	return dentry;

}