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Commit 9a9686b6 authored by Li Zefan's avatar Li Zefan Committed by Paul E. McKenney
Browse files

cgroup: Fix an RCU warning in cgroup_path() 



with CONFIG_PROVE_RCU=y, a warning can be triggered:

  # mount -t cgroup -o debug xxx /mnt
  # cat /proc/$$/cgroup

...
kernel/cgroup.c:1649 invoked rcu_dereference_check() without protection!
...

This is a false-positive, because cgroup_path() can be called
with either rcu_read_lock() held or cgroup_mutex held.

Signed-off-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent e35ec2d2

kernel/cgroup.c

+9 −3
Original line number Diff line number Diff line
@@ -1646,7 +1646,9 @@ static inline struct cftype *__d_cft(struct dentry *dentry) 
int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)

{

	char *start;

	struct dentry *dentry = rcu_dereference(cgrp->dentry);

	struct dentry *dentry = rcu_dereference_check(cgrp->dentry,

						      rcu_read_lock_held() ||

						      cgroup_lock_is_held());



	if (!dentry || cgrp == dummytop) {

		/*
@@ -1662,13 +1664,17 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen) 
	*--start = '\0';

	for (;;) {

		int len = dentry->d_name.len;



		if ((start -= len) < buf)

			return -ENAMETOOLONG;

		memcpy(start, cgrp->dentry->d_name.name, len);

		memcpy(start, dentry->d_name.name, len);

		cgrp = cgrp->parent;

		if (!cgrp)

			break;

		dentry = rcu_dereference(cgrp->dentry);



		dentry = rcu_dereference_check(cgrp->dentry,

					       rcu_read_lock_held() ||

					       cgroup_lock_is_held());

		if (!cgrp->parent)

			continue;

		if (--start < buf)