cgroup: simplify threadgroup locking
Now that threadgroup locking is made global, code paths around it can be simplified. * lock-verify-unlock-retry dancing removed from __cgroup_procs_write(). * Race protection against de_thread() removed from cgroup_update_dfl_csses(). Signed-off-by: Tejun Heo <tj@kernel.org>
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d59cfc09c3
commit
b5ba75b5fc
1 changed files with 13 additions and 35 deletions
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@ -2402,14 +2402,13 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
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if (!cgrp)
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return -ENODEV;
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retry_find_task:
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percpu_down_write(&cgroup_threadgroup_rwsem);
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rcu_read_lock();
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if (pid) {
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tsk = find_task_by_vpid(pid);
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if (!tsk) {
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rcu_read_unlock();
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ret = -ESRCH;
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goto out_unlock_cgroup;
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goto out_unlock_rcu;
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}
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/*
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* even if we're attaching all tasks in the thread group, we
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@ -2419,9 +2418,8 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
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if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
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!uid_eq(cred->euid, tcred->uid) &&
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!uid_eq(cred->euid, tcred->suid)) {
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rcu_read_unlock();
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ret = -EACCES;
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goto out_unlock_cgroup;
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goto out_unlock_rcu;
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}
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} else
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tsk = current;
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@ -2436,35 +2434,21 @@ static ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
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*/
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if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
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ret = -EINVAL;
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rcu_read_unlock();
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goto out_unlock_cgroup;
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goto out_unlock_rcu;
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}
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get_task_struct(tsk);
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rcu_read_unlock();
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percpu_down_write(&cgroup_threadgroup_rwsem);
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if (threadgroup) {
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if (!thread_group_leader(tsk)) {
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/*
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* a race with de_thread from another thread's exec()
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* may strip us of our leadership, if this happens,
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* there is no choice but to throw this task away and
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* try again; this is
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* "double-double-toil-and-trouble-check locking".
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*/
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percpu_up_write(&cgroup_threadgroup_rwsem);
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put_task_struct(tsk);
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goto retry_find_task;
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}
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}
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ret = cgroup_attach_task(cgrp, tsk, threadgroup);
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percpu_up_write(&cgroup_threadgroup_rwsem);
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put_task_struct(tsk);
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out_unlock_cgroup:
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goto out_unlock_threadgroup;
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out_unlock_rcu:
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rcu_read_unlock();
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out_unlock_threadgroup:
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percpu_up_write(&cgroup_threadgroup_rwsem);
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cgroup_kn_unlock(of->kn);
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return ret ?: nbytes;
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}
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@ -2611,6 +2595,8 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
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lockdep_assert_held(&cgroup_mutex);
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percpu_down_write(&cgroup_threadgroup_rwsem);
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/* look up all csses currently attached to @cgrp's subtree */
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down_read(&css_set_rwsem);
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css_for_each_descendant_pre(css, cgroup_css(cgrp, NULL)) {
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@ -2666,17 +2652,8 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
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goto out_finish;
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last_task = task;
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percpu_down_write(&cgroup_threadgroup_rwsem);
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/* raced against de_thread() from another thread? */
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if (!thread_group_leader(task)) {
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percpu_up_write(&cgroup_threadgroup_rwsem);
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put_task_struct(task);
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continue;
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}
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ret = cgroup_migrate(src_cset->dfl_cgrp, task, true);
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percpu_up_write(&cgroup_threadgroup_rwsem);
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put_task_struct(task);
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if (WARN(ret, "cgroup: failed to update controllers for the default hierarchy (%d), further operations may crash or hang\n", ret))
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@ -2686,6 +2663,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
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out_finish:
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cgroup_migrate_finish(&preloaded_csets);
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percpu_up_write(&cgroup_threadgroup_rwsem);
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return ret;
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}
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