diff options
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r-- | kernel/cgroup.c | 57 |
1 files changed, 23 insertions, 34 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 145deeb69bc3..ad447684aa47 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -386,10 +386,22 @@ static void free_css_set_work(struct work_struct *work) struct cgroup *cgrp = link->cgrp; list_del(&link->cg_link_list); list_del(&link->cgrp_link_list); - if (atomic_dec_and_test(&cgrp->count)) { + + + /* + * We may not be holding cgroup_mutex, and if cgrp->count is + * dropped to 0 the cgroup can be destroyed at any time, hence + * rcu_read_lock is used to keep it alive. + */ + rcu_read_lock(); + if (atomic_dec_and_test(&cgrp->count) && + notify_on_release(cgrp)) { check_for_release(cgrp); cgroup_wakeup_rmdir_waiter(cgrp); } + + rcu_read_unlock(); + kfree(link); } write_unlock(&css_set_lock); @@ -1878,9 +1890,8 @@ static void cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp, * trading it for newcg is protected by cgroup_mutex, we're safe to drop * it here; it will be freed under RCU. */ - put_css_set(oldcg); - set_bit(CGRP_RELEASABLE, &oldcgrp->flags); + put_css_set(oldcg); } /** @@ -2623,9 +2634,7 @@ static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry, dentry->d_fsdata = cgrp; inc_nlink(parent->d_inode); rcu_assign_pointer(cgrp->dentry, dentry); - dget(dentry); } - dput(dentry); return error; } @@ -4533,31 +4542,20 @@ static const struct file_operations proc_cgroupstats_operations = { * * A pointer to the shared css_set was automatically copied in * fork.c by dup_task_struct(). However, we ignore that copy, since - * it was not made under the protection of RCU, cgroup_mutex or - * threadgroup_change_begin(), so it might no longer be a valid - * cgroup pointer. cgroup_attach_task() might have already changed - * current->cgroups, allowing the previously referenced cgroup - * group to be removed and freed. - * - * Outside the pointer validity we also need to process the css_set - * inheritance between threadgoup_change_begin() and - * threadgoup_change_end(), this way there is no leak in any process - * wide migration performed by cgroup_attach_proc() that could otherwise - * miss a thread because it is too early or too late in the fork stage. + * it was not made under the protection of RCU or cgroup_mutex, so + * might no longer be a valid cgroup pointer. cgroup_attach_task() might + * have already changed current->cgroups, allowing the previously + * referenced cgroup group to be removed and freed. * * At the point that cgroup_fork() is called, 'current' is the parent * task, and the passed argument 'child' points to the child task. */ void cgroup_fork(struct task_struct *child) { - /* - * We don't need to task_lock() current because current->cgroups - * can't be changed concurrently here. The parent obviously hasn't - * exited and called cgroup_exit(), and we are synchronized against - * cgroup migration through threadgroup_change_begin(). - */ + task_lock(current); child->cgroups = current->cgroups; get_css_set(child->cgroups); + task_unlock(current); INIT_LIST_HEAD(&child->cg_list); } @@ -4610,19 +4608,10 @@ void cgroup_post_fork(struct task_struct *child) */ if (use_task_css_set_links) { write_lock(&css_set_lock); - if (list_empty(&child->cg_list)) { - /* - * It's safe to use child->cgroups without task_lock() - * here because we are protected through - * threadgroup_change_begin() against concurrent - * css_set change in cgroup_task_migrate(). Also - * the task can't exit at that point until - * wake_up_new_task() is called, so we are protected - * against cgroup_exit() setting child->cgroup to - * init_css_set. - */ + task_lock(child); + if (list_empty(&child->cg_list)) list_add(&child->cg_list, &child->cgroups->tasks); - } + task_unlock(child); write_unlock(&css_set_lock); } } |