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cgroup: always use RCU accessors for protected accesses

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kernel/cgroup.c still has places where a RCU pointer is set and
accessed directly without going through RCU_INIT_POINTER() or
rcu_dereference_protected().  They're all properly protected accesses
so nothing is broken but it leads to spurious sparse RCU address space
warnings.

Substitute direct accesses with RCU_INIT_POINTER() and
rcu_dereference_protected().  Note that %true is specified as the
extra condition for all derference updates.  This isn't ideal as all
it does is suppressing warning without actually policing
synchronization rules; however, most are scheduled to be removed
pretty soon along with css_id itself, so no reason to be more
elaborate.

Combined with the previous changes, this removes all RCU related
sparse warnings from cgroup.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Acked-by; Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2013-06-21 15:52:33 -07:00
parent a8ad805cfd
commit a4ea1cc906
1 changed files with 12 additions and 9 deletions
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21
kernel/cgroup.c
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@ -1427,7 +1427,7 @@ static void init_cgroup_root(struct cgroupfs_root *root)
INIT_LIST_HEAD(&root->root_list);
root->number_of_cgroups = 1;
cgrp->root = root;
cgrp->name = &root_cgroup_name;
RCU_INIT_POINTER(cgrp->name, &root_cgroup_name);
init_cgroup_housekeeping(cgrp);
}
@ -2558,7 +2558,7 @@ static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry,
return ret;
}
old_name = cgrp->name;
old_name = rcu_dereference_protected(cgrp->name, true);
rcu_assign_pointer(cgrp->name, name);
kfree_rcu(old_name, rcu_head);
@ -4177,13 +4177,15 @@ static int cgroup_populate_dir(struct cgroup *cgrp, bool base_files,
/* This cgroup is ready now */
for_each_root_subsys(cgrp->root, ss) {
struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
struct css_id *id = rcu_dereference_protected(css->id, true);
/*
* Update id->css pointer and make this css visible from
* CSS ID functions. This pointer will be dereferened
* from RCU-read-side without locks.
*/
if (css->id)
rcu_assign_pointer(css->id->css, css);
if (id)
rcu_assign_pointer(id->css, css);
}
return 0;
@ -4863,7 +4865,7 @@ int __init cgroup_init_early(void)
css_set_count = 1;
init_cgroup_root(&cgroup_dummy_root);
cgroup_root_count = 1;
init_task.cgroups = &init_css_set;
RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
init_cgrp_cset_link.cset = &init_css_set;
init_cgrp_cset_link.cgrp = cgroup_dummy_top;
@ -5380,7 +5382,8 @@ bool css_is_ancestor(struct cgroup_subsys_state *child,
void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
{
struct css_id *id = css->id;
struct css_id *id = rcu_dereference_protected(css->id, true);
/* When this is called before css_id initialization, id can be NULL */
if (!id)
return;
@ -5446,8 +5449,8 @@ static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss,
return PTR_ERR(newid);
newid->stack[0] = newid->id;
newid->css = rootcss;
rootcss->id = newid;
RCU_INIT_POINTER(newid->css, rootcss);
RCU_INIT_POINTER(rootcss->id, newid);
return 0;
}
@ -5461,7 +5464,7 @@ static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
subsys_id = ss->subsys_id;
parent_css = parent->subsys[subsys_id];
child_css = child->subsys[subsys_id];
parent_id = parent_css->id;
parent_id = rcu_dereference_protected(parent_css->id, true);
depth = parent_id->depth + 1;
child_id = get_new_cssid(ss, depth);