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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>
This commit is contained in:
Tejun Heo 2013-08-13 11:01:55 -04:00
parent 105347ba5d
commit 73e80ed800
2 changed files with 15 additions and 6 deletions
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2
include/linux/cgroup.h
View File

@ -204,7 +204,7 @@ struct cgroup {
struct cgroup_name __rcu *name;
/* Private pointers for each registered subsystem */
struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];
struct cgroupfs_root *root;

19
kernel/cgroup.c
View File

@ -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);
}