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authorTejun Heo <tj@kernel.org>2014-02-08 10:26:34 -0500
committerTejun Heo <tj@kernel.org>2014-02-08 10:26:34 -0500
commit48573a893303986e3b0b2974d6fb11f3d1bb7064 (patch)
treea01edf5728485e7637a25b08020f210a3ae0d67e
parentb58c89986a77a23658682a100eb15d8edb571ebb (diff)
downloadlinux-48573a893303986e3b0b2974d6fb11f3d1bb7064.tar.gz
cgroup: fix locking in cgroup_cfts_commit()
cgroup_cfts_commit() walks the cgroup hierarchy that the target subsystem is attached to and tries to apply the file changes. Due to the convolution with inode locking, it can't keep cgroup_mutex locked while iterating. It currently holds only RCU read lock around the actual iteration and then pins the found cgroup using dget(). Unfortunately, this is incorrect. Although the iteration does check cgroup_is_dead() before invoking dget(), there's nothing which prevents the dentry from going away inbetween. Note that this is different from the usual css iterations where css_tryget() is used to pin the css - css_tryget() tests whether the css can be pinned and fails if not. The problem can be solved by simply holding cgroup_mutex instead of RCU read lock around the iteration, which actually reduces LOC. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> Cc: stable@vger.kernel.org
-rw-r--r--kernel/cgroup.c11
1 files changed, 2 insertions, 9 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 0eb7b868e1a..3edf7163b84 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2763,10 +2763,7 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add)
*/
update_before = cgroup_serial_nr_next;
- mutex_unlock(&cgroup_mutex);
-
/* add/rm files for all cgroups created before */
- rcu_read_lock();
css_for_each_descendant_pre(css, cgroup_css(root, ss)) {
struct cgroup *cgrp = css->cgroup;
@@ -2775,23 +2772,19 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add)
inode = cgrp->dentry->d_inode;
dget(cgrp->dentry);
- rcu_read_unlock();
-
dput(prev);
prev = cgrp->dentry;
+ mutex_unlock(&cgroup_mutex);
mutex_lock(&inode->i_mutex);
mutex_lock(&cgroup_mutex);
if (cgrp->serial_nr < update_before && !cgroup_is_dead(cgrp))
ret = cgroup_addrm_files(cgrp, cfts, is_add);
- mutex_unlock(&cgroup_mutex);
mutex_unlock(&inode->i_mutex);
-
- rcu_read_lock();
if (ret)
break;
}
- rcu_read_unlock();
+ mutex_unlock(&cgroup_mutex);
dput(prev);
deactivate_super(sb);
return ret;