[CRIU] [PATCH 02/10] pstree: make helper items for pgid replaceable

[Pavel Tikhomirov]

If process group leader pid level is > than our pid level we will
see only part of a group leaders's pid in /proc/pid/status in NSpgid
field. So if we add such a pgid first with lookup_create_pid, adding
the leader later would fail.

Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 criu/include/pstree.h |  2 ++
 criu/pstree.c         | 60 +++++++++++++++++++++++++++++++++++++++++++++------
 2 files changed, 55 insertions(+), 7 deletions(-)

diff --git a/criu/include/pstree.h b/criu/include/pstree.h
index a3d8c31..3817694 100644
--- a/criu/include/pstree.h
+++ b/criu/include/pstree.h
@@ -31,6 +31,8 @@ struct pstree_item {
 	};
 	struct ns_id		*user_ns;
 	struct ns_id		*pid_for_children_ns;
+
+	int			replaceable;
 };
 
 #define vpid(item)	(item->pid->ns[0].virt)
diff --git a/criu/pstree.c b/criu/pstree.c
index a2744c4..e712dd3 100644
--- a/criu/pstree.c
+++ b/criu/pstree.c
@@ -530,7 +530,7 @@ static struct pid *find_pid_or_place_in_hier(struct rb_node **root, pid_t pid, i
  * it is not there yet. If pid_node isn't set, pstree_item
  * is inserted.
  */
-static struct pid *lookup_create_pid(pid_t *pid, int level, struct pid *pid_node, int ns_id)
+static struct pid *__lookup_create_pid(pid_t *pid, int level, struct pid *pid_node, int ns_id, int replaceable)
 {
 	struct rb_node **new = NULL, *parent = NULL;
 	struct pid *found;
@@ -565,16 +565,42 @@ static struct pid *lookup_create_pid(pid_t *pid, int level, struct pid *pid_node
 		if (item == NULL)
 			return NULL;
 
+		if (replaceable)
+			item->replaceable = true;
+
 		for (i = 0; i < level; i++)
 			item->pid->ns[i].virt = pid[i];
 		pid_node = item->pid;
 	}
 
 	for (i = level-1; i >= 0; i--) {
+
+again:
 		found = find_pid_or_place_in_hier(&ns->pid.rb_root.rb_node, pid[i], i, &parent, &new);
 		if (found) {
-			pr_err("pid is already linked\n");
-			return NULL;
+			if (found->item->replaceable) {
+				int j;
+				struct ns_id *tmp = ns;
+
+				pr_info("%d: Removing old (short cut) pid on all lower levels", found->ns[0].virt);
+				for (j = i; j >= 0; j--) {
+					BUG_ON(pid_node->ns[j].virt != found->ns[j].virt);
+					rb_erase(&found->ns[j].node, &tmp->pid.rb_root);
+					tmp = tmp->parent;
+					if (!tmp && j) {
+						pr_err("tmp ns has no parent\n");
+						return NULL;
+					}
+				}
+				/*
+				 * Just leave these pid and found item unlinked and unused,
+				 * it seems that we can't do anything with it here.
+				 */
+				goto again;
+			} else {
+				pr_err("pid is already linked\n");
+				return NULL;
+			}
 		}
 		if (!pid[i]) {
 			pr_err("Zero pid level\n");
@@ -590,6 +616,11 @@ static struct pid *lookup_create_pid(pid_t *pid, int level, struct pid *pid_node
 	return pid_node;
 }
 
+static struct pid *lookup_create_pid(pid_t *pid, int level, struct pid *pid_node, int ns_id)
+{
+	return __lookup_create_pid(pid, level, pid_node, ns_id, false);
+}
+
 void pstree_insert_pid(struct pid *pid_node, uint32_t ns_id)
 {
 	struct pid* n;
@@ -605,11 +636,11 @@ void pstree_insert_pid(struct pid *pid_node, uint32_t ns_id)
 	BUG_ON(n != pid_node);
 }
 
-struct pstree_item *lookup_create_item(pid_t *pid, int level, uint32_t ns_id)
+struct pstree_item *__lookup_create_item(pid_t *pid, int level, uint32_t ns_id, int replaceable)
 {
 	struct pid *node;;
 
-	node = lookup_create_pid(pid, level, NULL, ns_id);
+	node = __lookup_create_pid(pid, level, NULL, ns_id, replaceable);
 	if (!node)
 		return NULL;
 	BUG_ON(node->state == TASK_THREAD);
@@ -617,6 +648,16 @@ struct pstree_item *lookup_create_item(pid_t *pid, int level, uint32_t ns_id)
 	return node->item;
 }
 
+struct pstree_item *lookup_create_item(pid_t *pid, int level, uint32_t ns_id)
+{
+	return __lookup_create_item(pid, level, ns_id, false);
+}
+
+struct pstree_item *lookup_replaceable_item(pid_t *pid, int level, uint32_t ns_id)
+{
+	return __lookup_create_item(pid, level, ns_id, true);
+}
+
 struct pid *__pstree_pid_by_virt(struct ns_id *ns, pid_t pid)
 {
 	struct rb_node *node = ns->pid.rb_root.rb_node;
@@ -821,10 +862,15 @@ static int read_pstree_image(pid_t *pid_max)
 		 * be initialized when we meet PstreeEntry with this pid or
 		 * we will create helpers for them.
 		 */
-		if (lookup_create_item((pid_t *)e->ns_pgid, e->n_ns_pgid, ids->pid_ns_id) == NULL)
-			break;
 		if (lookup_create_item((pid_t *)e->ns_sid, e->n_ns_sid, ids->pid_ns_id) == NULL)
 			break;
+		/*
+		 * Pgid can be cut by level of current task
+		 * when process group leader is in several
+		 * nested pidns'es so mark it as replaceable.
+		 */
+		if (lookup_replaceable_item((pid_t *)e->ns_pgid, e->n_ns_pgid, ids->pid_ns_id) == NULL)
+			break;
 
 		BUG_ON(vpid(pi) != e->ns_pid[0]);
 		if (e->ns_pid[0] > *pid_max)
-- 
2.9.4