Revert "cgroup: remove redundant variable in cgroup_mount()" (e756c7b6) · Commits · 戴 / test

This reverts commit . 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:

Andrey Wagin <avagin@gmail.com> Signed-off-by:

Zefan Li <lizefan@huawei.com> Signed-off-by:

Tejun Heo <tj@kernel.org>

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 @@ out_free:
		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;
		}

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