From a8ad805cfde00be8fe3b3dae8890996dbeb91e2c Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 21 Jun 2013 15:52:04 -0700 Subject: cgroup: fix RCU accesses around task->cgroups There are several places in kernel/cgroup.c where task->cgroups is accessed and modified without going through proper RCU accessors. None is broken as they're all lock protected accesses; however, this still triggers sparse RCU address space warnings. * Consistently use task_css_set() for task->cgroups dereferencing. * Use RCU_INIT_POINTER() to clear task->cgroups to &init_css_set on exit. * Remove unnecessary rcu_dereference_raw() from cset->subsys[] dereference in cgroup_exit(). Signed-off-by: Tejun Heo Reported-by: Fengguang Wu Acked-by: Li Zefan --- kernel/cgroup.c | 24 +++++++++++++----------- 1 file changed, 13 insertions(+), 11 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 2d3a132e881d..ee9f0c1c8bff 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -724,7 +724,7 @@ static struct cgroup *task_cgroup_from_root(struct task_struct *task, * task can't change groups, so the only thing that can happen * is that it exits and its css is set back to init_css_set. */ - cset = task->cgroups; + cset = task_css_set(task); if (cset == &init_css_set) { res = &root->top_cgroup; } else { @@ -1971,7 +1971,7 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp, * css_set to init_css_set and dropping the old one. */ WARN_ON_ONCE(tsk->flags & PF_EXITING); - old_cset = tsk->cgroups; + old_cset = task_css_set(tsk); task_lock(tsk); rcu_assign_pointer(tsk->cgroups, new_cset); @@ -2094,8 +2094,11 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk, * we use find_css_set, which allocates a new one if necessary. */ for (i = 0; i < group_size; i++) { + struct css_set *old_cset; + tc = flex_array_get(group, i); - tc->cg = find_css_set(tc->task->cgroups, cgrp); + old_cset = task_css_set(tc->task); + tc->cg = find_css_set(old_cset, cgrp); if (!tc->cg) { retval = -ENOMEM; goto out_put_css_set_refs; @@ -3012,7 +3015,7 @@ static void cgroup_enable_task_cg_lists(void) * entry won't be deleted though the process has exited. */ if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list)) - list_add(&p->cg_list, &p->cgroups->tasks); + list_add(&p->cg_list, &task_css_set(p)->tasks); task_unlock(p); } while_each_thread(g, p); read_unlock(&tasklist_lock); @@ -5061,8 +5064,8 @@ static const struct file_operations proc_cgroupstats_operations = { void cgroup_fork(struct task_struct *child) { task_lock(current); + get_css_set(task_css_set(current)); child->cgroups = current->cgroups; - get_css_set(child->cgroups); task_unlock(current); INIT_LIST_HEAD(&child->cg_list); } @@ -5097,7 +5100,7 @@ void cgroup_post_fork(struct task_struct *child) write_lock(&css_set_lock); task_lock(child); if (list_empty(&child->cg_list)) - list_add(&child->cg_list, &child->cgroups->tasks); + list_add(&child->cg_list, &task_css_set(child)->tasks); task_unlock(child); write_unlock(&css_set_lock); } @@ -5177,8 +5180,8 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks) /* Reassign the task to the init_css_set. */ task_lock(tsk); - cset = tsk->cgroups; - tsk->cgroups = &init_css_set; + cset = task_css_set(tsk); + RCU_INIT_POINTER(tsk->cgroups, &init_css_set); if (run_callbacks && need_forkexit_callback) { /* @@ -5187,8 +5190,7 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks) */ for_each_builtin_subsys(ss, i) { if (ss->exit) { - struct cgroup *old_cgrp = - rcu_dereference_raw(cset->subsys[i])->cgroup; + struct cgroup *old_cgrp = cset->subsys[i]->cgroup; struct cgroup *cgrp = task_cgroup(tsk, i); ss->exit(cgrp, old_cgrp, tsk); @@ -5555,7 +5557,7 @@ static u64 current_css_set_refcount_read(struct cgroup *cgrp, u64 count; rcu_read_lock(); - count = atomic_read(¤t->cgroups->refcount); + count = atomic_read(&task_css_set(current)->refcount); rcu_read_unlock(); return count; } -- cgit v1.2.3