If a task has exited to the point it has called cgroup_exit() already, then we can't migrate it to another cgroup anymore. This can happen when we are attaching a task to a new cgroup between the call to ->can_attach_task() on subsystems and the migration that is eventually tried in cgroup_task_migrate(). In this case cgroup_task_migrate() returns -ESRCH and we don't want to attach the task to the subsystems because the attachment to the new cgroup itself failed. Fix this by only calling ->attach_task() on the subsystems if the cgroup migration succeeded.
Unified · Split
| @@ -2135,14 +2135,17 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) · 2134 unmodified lines | ||
| 2135 | 2135 | oldcgrp = task_cgroup_from_root(tsk, root); |
| 2136 | 2136 | if (cgrp == oldcgrp) |
| 2137 | 2137 | continue; |
| 2138 | − /* attach each task to each subsystem */ | |
| 2139 | − for_each_subsys(root, ss) { | |
| 2140 | − if (ss->attach_task) | |
| 2141 | − ss->attach_task(cgrp, tsk); | |
| 2142 | − } | |
| 2143 | 2138 | /* if the thread is PF_EXITING, it can just get skipped. */ |
| 2144 | 2139 | retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, true); |
| 2145 | − BUG_ON(retval != 0 && retval != -ESRCH); | |
| 2140 | + if (retval == 0) { | |
| 2141 | + /* attach each task to each subsystem */ | |
| 2142 | + for_each_subsys(root, ss) { | |
| 2143 | + if (ss->attach_task) | |
| 2144 | + ss->attach_task(cgrp, tsk); | |
| 2145 | + } | |
| 2146 | + } else { | |
| 2147 | + BUG_ON(retval != -ESRCH); | |
| 2148 | + } | |
| 2146 | 2149 | } |
| 2147 | 2150 | /* nothing is sensitive to fork() after this point. */ |
| 2148 | 2151 | |