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authorTejun Heo <tj@kernel.org>2013-08-13 11:01:55 -0400
committerTejun Heo <tj@kernel.org>2013-08-13 11:01:55 -0400
commit73e80ed8007fc48a6deeb295ba37159fad274bd2 (patch)
treec4f430a223725038cb85be6ee0e13578d831c929 /kernel/cgroup.c
parent105347ba5da3e87facce2337c50cd5df93cc6bec (diff)
downloadlinux-73e80ed8007fc48a6deeb295ba37159fad274bd2.tar.bz2
cgroup: add __rcu modifier to cgroup->subsys[]
For the planned unified hierarchy, each css (cgroup_subsys_state) will be RCU protected so that it can be created and destroyed individually while allowing RCU accesses. Previous changes ensured that all cgroup->subsys[] accesses use the cgroup_css() accessor. This patch adds __rcu modifier to cgroup->subsys[], add matching RCU dereference in cgroup_css() and convert all assignments to either rcu_assign_pointer() or RCU_INIT_POINTER(). This change prepares for the actual RCUfication of css's and doesn't introduce any visible behavior change. The conversion is verified with sparse and all accesses are properly RCU annotated. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com>
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r--kernel/cgroup.c19
1 files changed, 14 insertions, 5 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d63beffd41e1..c27101622567 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -229,11 +229,16 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
* @subsys_id: the subsystem of interest
*
* Return @cgrp's css (cgroup_subsys_state) associated with @subsys_id.
+ * This function must be called either under cgroup_mutex or
+ * rcu_read_lock() and the caller is responsible for pinning the returned
+ * css if it wants to keep accessing it outside the said locks. This
+ * function may return %NULL if @cgrp doesn't have @subsys_id enabled.
*/
static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
int subsys_id)
{
- return cgrp->subsys[subsys_id];
+ return rcu_dereference_check(cgrp->subsys[subsys_id],
+ lockdep_is_held(&cgroup_mutex));
}
/* convenient tests for these bits */
@@ -1072,8 +1077,10 @@ static int rebind_subsystems(struct cgroupfs_root *root,
BUG_ON(!cgroup_css(cgroup_dummy_top, i));
BUG_ON(cgroup_css(cgroup_dummy_top, i)->cgroup != cgroup_dummy_top);
- cgrp->subsys[i] = cgroup_dummy_top->subsys[i];
+ rcu_assign_pointer(cgrp->subsys[i],
+ cgroup_css(cgroup_dummy_top, i));
cgroup_css(cgrp, i)->cgroup = cgrp;
+
list_move(&ss->sibling, &root->subsys_list);
ss->root = root;
if (ss->bind)
@@ -1088,8 +1095,10 @@ static int rebind_subsystems(struct cgroupfs_root *root,
if (ss->bind)
ss->bind(cgroup_css(cgroup_dummy_top, i));
+
cgroup_css(cgroup_dummy_top, i)->cgroup = cgroup_dummy_top;
- cgrp->subsys[i] = NULL;
+ RCU_INIT_POINTER(cgrp->subsys[i], NULL);
+
cgroup_subsys[i]->root = &cgroup_dummy_root;
list_move(&ss->sibling, &cgroup_dummy_root.subsys_list);
@@ -4314,7 +4323,7 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
css->flags |= CSS_ROOT;
BUG_ON(cgroup_css(cgrp, ss->subsys_id));
- cgrp->subsys[ss->subsys_id] = css;
+ rcu_assign_pointer(cgrp->subsys[ss->subsys_id], css);
}
/* invoke ->css_online() on a new CSS and mark it online if successful */
@@ -4962,7 +4971,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
* also takes care of freeing the css_id.
*/
ss->css_free(cgroup_css(cgroup_dummy_top, ss->subsys_id));
- cgroup_dummy_top->subsys[ss->subsys_id] = NULL;
+ RCU_INIT_POINTER(cgroup_dummy_top->subsys[ss->subsys_id], NULL);
mutex_unlock(&cgroup_mutex);
}