[CRIU] [PATCH 4/5] pstree: try to find a free pid between busy pids

[Andrey Vagin]

From: Andrew Vagin <avagin at virtuozzo.com>

Currently our pid allocator returns max_pid++ and it can return a pid
which is bigger than kernel.max_pid.

(00.821430)   5506: Error (cr-restore.c:1540): Pid 300 do not match expected 32768

https://jira.sw.ru/browse/PSBM-42202
Signed-off-by: Andrew Vagin <avagin at virtuozzo.com>
---
 criu/pstree.c | 93 +++++++++++++++++++++++++++++++++++------------------------
 1 file changed, 56 insertions(+), 37 deletions(-)

diff --git a/criu/pstree.c b/criu/pstree.c
index 1be8c48..61fd5d3 100644
--- a/criu/pstree.c
+++ b/criu/pstree.c
@@ -331,8 +331,6 @@ err:
 	return ret;
 }
 
-static int max_pid = 0;
-
 static int prepare_pstree_for_shell_job(void)
 {
 	pid_t current_sid = getsid(getpid());
@@ -379,8 +377,8 @@ static int prepare_pstree_for_shell_job(void)
 			pi->sid = current_sid;
 	}
 
-	max_pid = max((int)current_sid, max_pid);
-	max_pid = max((int)current_gid, max_pid);
+	insert_item(current_sid);
+	insert_item(current_gid);
 
 	return 0;
 }
@@ -459,11 +457,8 @@ static int read_pstree_image(void)
 			break;
 
 		pi->pid.virt = e->pid;
-		max_pid = max((int)e->pid, max_pid);
 		pi->pgid = e->pgid;
-		max_pid = max((int)e->pgid, max_pid);
 		pi->sid = e->sid;
-		max_pid = max((int)e->sid, max_pid);
 		pi->pid.state = TASK_ALIVE;
 
 		if (e->ppid == 0) {
@@ -543,11 +538,34 @@ static int read_pstree_image(void)
 				goto err;
 		}
 	}
+
 err:
 	close_image(img);
 	return ret;
 }
 
+#define RESERVED_PIDS           300
+static int get_free_pid()
+{
+	static struct pstree_item *prev, *next;
+
+	if (prev == NULL)
+		prev = rb_entry(rb_first(&root_rb), struct pstree_item, pid.node);
+
+	while (1) {
+		pid_t pid;
+		pid = prev->pid.virt + 1;
+		pid = pid < RESERVED_PIDS ? RESERVED_PIDS + 1 : pid;
+
+		next = rb_entry(rb_next(&prev->pid.node), struct pstree_item, pid.node);
+		if (&next->pid.node == NULL || next->pid.virt > pid)
+			return pid;
+		prev = next;
+	}
+
+	return -1;
+}
+
 static int prepare_pstree_ids(void)
 {
 	struct pstree_item *item, *child, *helper, *tmp;
@@ -562,6 +580,7 @@ static int prepare_pstree_ids(void)
 	 * reparented to init.
 	 */
 	list_for_each_entry(item, &root_item->children, sibling) {
+		struct pstree_item *leader;
 
 		/*
 		 * If a child belongs to the root task's session or it's
@@ -571,15 +590,36 @@ static int prepare_pstree_ids(void)
 		if (item->sid == root_item->sid || item->sid == item->pid.virt)
 			continue;
 
-		helper = alloc_pstree_helper();
-		if (helper == NULL)
-			return -1;
-		helper->sid = item->sid;
-		helper->pgid = item->sid;
-		helper->pid.virt = item->sid;
-		helper->parent = root_item;
-		helper->ids = root_item->ids;
-		list_add_tail(&helper->sibling, &helpers);
+		leader = insert_item(item->sid);
+		if (leader->pid.state != TASK_UNDEF) {
+			pid_t pid;
+
+			pid = get_free_pid();
+			if (pid < 0)
+				break;
+			helper = insert_item(pid);
+			if (helper == NULL)
+				return -1;
+
+			pr_info("Session leader %d\n", item->sid);
+
+			helper->sid = item->sid;
+			helper->pgid = leader->pgid;
+			helper->ids = leader->ids;
+			helper->parent = leader;
+			list_add(&helper->sibling, &leader->children);
+
+			pr_info("Attach %d to the task %d\n",
+					helper->pid.virt, leader->pid.virt);
+		} else {
+			helper = leader;
+			helper->sid = item->sid;
+			helper->pgid = item->sid;
+			helper->parent = root_item;
+			helper->ids = root_item->ids;
+			list_add_tail(&helper->sibling, &helpers);
+		}
+		init_pstree_helper(helper);
 
 		pr_info("Add a helper %d for restoring SID %d\n",
 				helper->pid.virt, helper->sid);
@@ -639,27 +679,6 @@ static int prepare_pstree_ids(void)
 
 			continue;
 		}
-
-		pr_info("Session leader %d\n", item->sid);
-
-		/* Try to find helpers, who should be connected to the leader */
-		list_for_each_entry(child, &helpers, sibling) {
-			if (child->pid.state != TASK_HELPER)
-				continue;
-
-			if (child->sid != item->sid)
-				continue;
-
-			child->pgid = item->pgid;
-			child->pid.virt = ++max_pid;
-			child->parent = item;
-			list_move(&child->sibling, &item->children);
-
-			pr_info("Attach %d to the task %d\n",
-					child->pid.virt, item->pid.virt);
-
-			break;
-		}
 	}
 
 	/* All other helpers are session leaders for own sessions */
-- 
2.5.0