@@ -1744,7 +1744,7 @@ EXPORT_SYMBOL_GPL(cgroup_path);
*
* 'guarantee' is set if the caller promises that a new css_set for the task
* will already exist. If not set, this function might sleep, and can fail with
- * -ENOMEM. Otherwise, it can only fail with -ESRCH.
+ * -ENOMEM. Must be called with cgroup_mutex and threadgroup locked.
*/
static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
struct task_struct *tsk, bool guarantee)
@@ -1782,13 +1782,9 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
}
put_css_set(oldcg);
- /* if PF_EXITING is set, the tsk->cgroups pointer is no longer safe. */
+ /* @tsk can't exit as its threadgroup is locked */
task_lock(tsk);
- if (tsk->flags & PF_EXITING) {
- task_unlock(tsk);
- put_css_set(newcg);
- return -ESRCH;
- }
+ WARN_ON_ONCE(tsk->flags & PF_EXITING);
rcu_assign_pointer(tsk->cgroups, newcg);
task_unlock(tsk);
@@ -1814,8 +1810,8 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
* @cgrp: the cgroup the task is attaching to
* @tsk: the task to be attached
*
- * Call holding cgroup_mutex. May take task_lock of
- * the task 'tsk' during call.
+ * Call with cgroup_mutex and threadgroup locked. May take task_lock of
+ * @tsk during call.
*/
int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
{
@@ -1824,6 +1820,10 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
struct cgroup *oldcgrp;
struct cgroupfs_root *root = cgrp->root;
+ /* @tsk either already exited or can't exit until the end */
+ if (tsk->flags & PF_EXITING)
+ return -ESRCH;
+
/* Nothing to do if the task is already in that cgroup */
oldcgrp = task_cgroup_from_root(tsk, root);
if (cgrp == oldcgrp)
@@ -2044,6 +2044,10 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
tsk = leader;
i = 0;
do {
+ /* @tsk either already exited or can't exit until the end */
+ if (tsk->flags & PF_EXITING)
+ continue;
+
/* as per above, nr_threads may decrease, but not increase. */
BUG_ON(i >= group_size);
get_task_struct(tsk);
@@ -2142,7 +2146,7 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
}
/* if the thread is PF_EXITING, it can just get skipped. */
retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, true);
- BUG_ON(retval != 0 && retval != -ESRCH);
+ BUG_ON(retval != 0);
}
/* nothing is sensitive to fork() after this point. */
@@ -2194,8 +2198,8 @@ out_free_group_list:
/*
* Find the task_struct of the task to attach by vpid and pass it along to the
- * function to attach either it or all tasks in its threadgroup. Will take
- * cgroup_mutex; may take task_lock of task.
+ * function to attach either it or all tasks in its threadgroup. Will lock
+ * cgroup_mutex and threadgroup; may take task_lock of task.
*/
static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
{
@@ -2218,10 +2222,6 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
* detect it later.
*/
tsk = tsk->group_leader;
- } else if (tsk->flags & PF_EXITING) {
- /* optimization for the single-task-only case */
- rcu_read_unlock();
- return -ESRCH;
}
/*
@@ -2245,8 +2245,7 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
get_task_struct(tsk);
}
- if (threadgroup)
- threadgroup_lock(tsk);
+ threadgroup_lock(tsk);
ret = -ENODEV;
if (cgroup_lock_live_group(cgrp)) {
if (threadgroup)
@@ -2255,8 +2254,7 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
ret = cgroup_attach_task(cgrp, tsk);
cgroup_unlock();
}
- if (threadgroup)
- threadgroup_unlock(tsk);
+ threadgroup_unlock(tsk);
put_task_struct(tsk);
return ret;
}