cgroup: make cgroup_update_dfl_csses() migrate all target processes atomically

[karo-tx-linux.git] / kernel / cgroup.c

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f24d3cedd809b593cb8a5df41073b5e7747f56f4..f924158a1b65641df28fa23e2988a0d2d9375126 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2799,6 +2799,7 @@ static int cgroup_subtree_control_show(struct seq_file *seq, void *v)
 static int cgroup_update_dfl_csses(struct cgroup *cgrp)
 {
        LIST_HEAD(preloaded_csets);
+       struct cgroup_taskset tset = CGROUP_TASKSET_INIT(tset);
        struct cgroup_subsys_state *css;
        struct css_set *src_cset;
        int ret;
@@ -2827,50 +2828,21 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp)
        if (ret)
                goto out_finish;
 
+       down_write(&css_set_rwsem);
        list_for_each_entry(src_cset, &preloaded_csets, mg_preload_node) {
-               struct task_struct *last_task = NULL, *task;
+               struct task_struct *task, *ntask;
 
                /* src_csets precede dst_csets, break on the first dst_cset */
                if (!src_cset->mg_src_cgrp)
                        break;
 
-               /*
-                * All tasks in src_cset need to be migrated to the
-                * matching dst_cset.  Empty it process by process.  We
-                * walk tasks but migrate processes.  The leader might even
-                * belong to a different cset but such src_cset would also
-                * be among the target src_csets because the default
-                * hierarchy enforces per-process membership.
-                */
-               while (true) {
-                       down_read(&css_set_rwsem);
-                       task = list_first_entry_or_null(&src_cset->tasks,
-                                               struct task_struct, cg_list);
-                       if (task) {
-                               task = task->group_leader;
-                               WARN_ON_ONCE(!task_css_set(task)->mg_src_cgrp);
-                               get_task_struct(task);
-                       }
-                       up_read(&css_set_rwsem);
-
-                       if (!task)
-                               break;
-
-                       /* guard against possible infinite loop */
-                       if (WARN(last_task == task,
-                                "cgroup: update_dfl_csses failed to make progress, aborting in inconsistent state\n"))
-                               goto out_finish;
-                       last_task = task;
-
-                       ret = cgroup_migrate(task, true, src_cset->dfl_cgrp);
-
-                       put_task_struct(task);
-
-                       if (WARN(ret, "cgroup: failed to update controllers for the default hierarchy (%d), further operations may crash or hang\n", ret))
-                               goto out_finish;
-               }
+               /* all tasks in src_csets need to be migrated */
+               list_for_each_entry_safe(task, ntask, &src_cset->tasks, cg_list)
+                       cgroup_taskset_add(task, &tset);
        }
+       up_write(&css_set_rwsem);
 
+       ret = cgroup_taskset_migrate(&tset, cgrp);
 out_finish:
        cgroup_migrate_finish(&preloaded_csets);
        percpu_up_write(&cgroup_threadgroup_rwsem);