diff options
| author | Tejun Heo <tj@kernel.org> | 2012-11-19 08:13:36 -0800 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2012-11-19 08:13:36 -0800 |
| commit | febfcef60d4f9457785b45aab548bc7ee5ea158f (patch) | |
| tree | 70fab0e8ec07aec4142f1dc228f307e6b1d79de0 | |
| parent | 4e139afc22cb98d0d032ffce0285bfcc73ca5217 (diff) | |
cgroup: cgroup->dentry isn't a RCU pointer
cgroup->dentry is marked and used as a RCU pointer; however, it isn't
one - the final dentry put doesn't go through call_rcu(). cgroup and
dentry share the same RCU freeing rule via synchronize_rcu() in
cgroup_diput() (kfree_rcu() used on cgrp is unnecessary). If cgrp is
accessible under RCU read lock, so is its dentry and dereferencing
cgrp->dentry doesn't need any further RCU protection or annotation.
While not being accurate, before the previous patch, the RCU accessors
served a purpose as memory barriers - cgroup->dentry used to be
assigned after the cgroup was made visible to cgroup_path(), so the
assignment and dereferencing in cgroup_path() needed the memory
barrier pair. Now that list_add_tail_rcu() happens after
cgroup->dentry is assigned, this no longer is necessary.
Remove the now unnecessary and misleading RCU annotations from
cgroup->dentry. To make up for the removal of rcu_dereference_check()
in cgroup_path(), add an explicit rcu_lockdep_assert(), which asserts
the dereference rule of @cgrp, not cgrp->dentry.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
| -rw-r--r-- | include/linux/cgroup.h | 2 | ||||
| -rw-r--r-- | kernel/cgroup.c | 11 |
2 files changed, 7 insertions, 6 deletions
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 8f64b459fbd..d605857c4bf 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -165,7 +165,7 @@ struct cgroup { struct list_head files; /* my files */ struct cgroup *parent; /* my parent */ - struct dentry __rcu *dentry; /* cgroup fs entry, RCU protected */ + struct dentry *dentry; /* cgroup fs entry, RCU protected */ /* Private pointers for each registered subsystem */ struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT]; diff --git a/kernel/cgroup.c b/kernel/cgroup.c index d62a529db2f..affc76d7f73 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -1756,9 +1756,11 @@ static struct kobject *cgroup_kobj; */ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen) { + struct dentry *dentry = cgrp->dentry; char *start; - struct dentry *dentry = rcu_dereference_check(cgrp->dentry, - cgroup_lock_is_held()); + + rcu_lockdep_assert(rcu_read_lock_held() || cgroup_lock_is_held(), + "cgroup_path() called without proper locking"); if (!dentry || cgrp == dummytop) { /* @@ -1782,8 +1784,7 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen) if (!cgrp) break; - dentry = rcu_dereference_check(cgrp->dentry, - cgroup_lock_is_held()); + dentry = cgrp->dentry; if (!cgrp->parent) continue; if (--start < buf) @@ -4124,7 +4125,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry, /* allocation complete, commit to creation */ dentry->d_fsdata = cgrp; - rcu_assign_pointer(cgrp->dentry, dentry); + cgrp->dentry = dentry; list_add_tail(&cgrp->allcg_node, &root->allcg_list); list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children); root->number_of_cgroups++; |