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.
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| @@ -2135,14 +2135,17 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) · 2134 unmodified lines | |||
| 2135 | oldcgrp = task_cgroup_from_root(tsk, root); | 2135 | oldcgrp = task_cgroup_from_root(tsk, root); |
| 2136 | if (cgrp == oldcgrp) | 2136 | if (cgrp == oldcgrp) |
| 2137 | continue; | 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 | /* if the thread is PF_EXITING, it can just get skipped. */ | 2138 | /* if the thread is PF_EXITING, it can just get skipped. */ |
| 2144 | retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, true); | 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 | /* nothing is sensitive to fork() after this point. */ | 2150 | /* nothing is sensitive to fork() after this point. */ |
| 2148 | 2151 | ||