Revert "cgroup: remove redundant variable in cgroup_mount()"
This reverts commit 0c7bf3e8cab7900e17ce7f97104c39927d835469.
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>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5eb20cd..f873c46 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1694,6 +1694,7 @@
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 @@
* 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 @@
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;
}
