!1411 [sync] PR-1408: Replace the hulk patch with the lts patch

Merge Pull Request from: @openeuler-sync-bot 
 

Origin pull request: 
https://gitee.com/openeuler/kernel/pulls/1408 
 
PR sync from: Gaosheng Cui <cuigaosheng1@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/KDI6HM6ETZD4MQLPN2PXX7TI3XO7ZJC5/ 
Replace the hulk patch with the lts patch, thanks!

Gaosheng Cui (1):
  Revert "cgroup: Stop task iteration when rebinding subsystem"

Xiu Jianfeng (1):
  cgroup: Do not corrupt task iteration when rebinding subsystem


-- 
2.30.0
 
https://gitee.com/openeuler/kernel/issues/I7AZ85 
 
Link:https://gitee.com/openeuler/kernel/pulls/1411 

Reviewed-by: Jialin Zhang <zhangjialin11@huawei.com> 
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com> 

include/linux/cgroup.h

@@ -47,7 +47,6 @@ struct kernel_clone_args;
 
 /* internal flags */
 #define CSS_TASK_ITER_SKIPPED		(1U << 16)
-#define CSS_TASK_ITER_STOPPED		(1U << 17)
 
 /* a css_task_iter should be treated as an opaque object */
 struct css_task_iter {

kernel/cgroup/cgroup.c

@@ -214,8 +214,6 @@ static int cgroup_apply_control(struct cgroup *cgrp);
 static void cgroup_finalize_control(struct cgroup *cgrp, int ret);
 static void css_task_iter_skip(struct css_task_iter *it,
 			       struct task_struct *task);
-static void css_task_iter_stop(struct css_task_iter *it,
-			       struct cgroup_subsys *ss);
 static int cgroup_destroy_locked(struct cgroup *cgrp);
 static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
 					      struct cgroup_subsys *ss);
@@ -856,19 +854,6 @@ static void css_set_skip_task_iters(struct css_set *cset,
 		css_task_iter_skip(it, task);
 }
 
-/*
- * @cset is moving to other list, it's not safe to continue the iteration,
- * because the cset_head of css_task_iter which is from the old list can
- * not be used as the stop condition of iteration.
- */
-static void css_set_stop_iters(struct css_set *cset, struct cgroup_subsys *ss)
-{
-	struct css_task_iter *it, *pos;
-
-	list_for_each_entry_safe(it, pos, &cset->task_iters, iters_node)
-		css_task_iter_stop(it, ss);
-}
-
 /**
  * css_set_move_task - move a task from one css_set to another
  * @task: task being moved
@@ -1727,7 +1712,7 @@ int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
 {
 	struct cgroup *dcgrp = &dst_root->cgrp;
 	struct cgroup_subsys *ss;
-	int ssid, i, ret;
+	int ssid, ret;
 	u16 dfl_disable_ss_mask = 0;
 
 	lockdep_assert_held(&cgroup_mutex);
@@ -1771,7 +1756,8 @@ int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
 		struct cgroup_root *src_root = ss->root;
 		struct cgroup *scgrp = &src_root->cgrp;
 		struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
-		struct css_set *cset;
+		struct css_set *cset, *cset_pos;
+		struct css_task_iter *it;
 
 		WARN_ON(!css || cgroup_css(dcgrp, ss));
 
@@ -1789,10 +1775,21 @@ int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
 		css->cgroup = dcgrp;
 
 		spin_lock_irq(&css_set_lock);
-		hash_for_each(css_set_table, i, cset, hlist) {
-			css_set_stop_iters(cset, ss);
+		WARN_ON(!list_empty(&dcgrp->e_csets[ss->id]));
+		list_for_each_entry_safe(cset, cset_pos, &scgrp->e_csets[ss->id],
+					 e_cset_node[ss->id]) {
 			list_move_tail(&cset->e_cset_node[ss->id],
 				       &dcgrp->e_csets[ss->id]);
+			/*
+			 * all css_sets of scgrp together in same order to dcgrp,
+			 * patch in-flight iterators to preserve correct iteration.
+			 * since the iterator is always advanced right away and
+			 * finished when it->cset_pos meets it->cset_head, so only
+			 * update it->cset_head is enough here.
+			 */
+			list_for_each_entry(it, &cset->task_iters, iters_node)
+				if (it->cset_head == &scgrp->e_csets[ss->id])
+					it->cset_head = &dcgrp->e_csets[ss->id];
 		}
 		spin_unlock_irq(&css_set_lock);
 
@@ -4681,16 +4678,6 @@ static void css_task_iter_skip(struct css_task_iter *it,
 	}
 }
 
-static void css_task_iter_stop(struct css_task_iter *it,
-			       struct cgroup_subsys *ss)
-{
-	lockdep_assert_held(&css_set_lock);
-
-	if (it->ss == ss) {
-		it->flags |= CSS_TASK_ITER_STOPPED;
-	}
-}
-
 static void css_task_iter_advance(struct css_task_iter *it)
 {
 	struct task_struct *task;
@@ -4794,11 +4781,6 @@ struct task_struct *css_task_iter_next(struct css_task_iter *it)
 
 	spin_lock_irq(&css_set_lock);
 
-	if (it->flags & CSS_TASK_ITER_STOPPED) {
-		spin_unlock_irq(&css_set_lock);
-		return NULL;
-	}
-
 	/* @it may be half-advanced by skips, finish advancing */
 	if (it->flags & CSS_TASK_ITER_SKIPPED)
 		css_task_iter_advance(it);