[CRIU] [PATCH 6/6] pstree: try to find a free pid between busy pids (v2)

[Pavel Emelyanov]

On 03/15/2016 09:37 AM, Andrey Vagin wrote:
> 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
> 
> v2: handle error code from insert_item()
> Signed-off-by: Andrew Vagin <avagin at virtuozzo.com>
> ---
>  criu/pstree.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 54 insertions(+), 9 deletions(-)
> 
> diff --git a/criu/pstree.c b/criu/pstree.c
> index 3a278fa..096abec 100644
> --- a/criu/pstree.c
> +++ b/criu/pstree.c
> @@ -325,8 +325,6 @@ err:
>  	return ret;
>  }
>  
> -static int max_pid = 0;
> -
>  static int prepare_pstree_for_shell_job(void)
>  {
>  	pid_t current_sid = getsid(getpid());
> @@ -373,12 +371,31 @@ 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);
> +	if (lookup_create_item(current_sid))
> +		return -1;
> +	if (lookup_create_item(current_gid))
> +		return -1;

This particular hunk seem to belong to different patch... #3?

>
>  	return 0;
>  }
>  
> +static struct pid *pstree_pid_by_virt(pid_t pid)
> +{
> +	struct rb_node *node = pid_root_rb.rb_node;
> +
> +	while (node) {
> +		struct pid *this = rb_entry(node, struct pid, node);
> +
> +		if (pid < this->virt)
> +			node = node->rb_left;
> +		else if (pid > this->virt)
> +			node = node->rb_right;
> +		else
> +			return this;
> +	}
> +	return NULL;
> +}
> +
>  /*
>   * Try to find a pid node in the tree and insert a new one,
>   * it is not there yet. If pid_node isn't set, pstree_item
> @@ -465,11 +482,8 @@ 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) {
> @@ -558,11 +572,34 @@ 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(&pid_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;
> @@ -578,6 +615,7 @@ static int prepare_pstree_ids(void)
>  	 */
>  	list_for_each_entry(item, &root_item->children, sibling) {
>  		struct pstree_item *leader;
> +		struct pid *node;
>  
>  		/*
>  		 * If a child belongs to the root task's session or it's
> @@ -587,9 +625,16 @@ static int prepare_pstree_ids(void)
>  		if (item->sid == root_item->sid || item->sid == item->pid.virt)
>  			continue;
>  
> -		leader = insert_item(item->sid);
> +		node = pstree_pid_by_virt(item->sid);
> +		BUG_ON(node == NULL);
> +		leader = container_of(node, struct pstree_item, pid);
>  		if (leader->pid.state != TASK_UNDEF) {
> -			helper = insert_item(++max_pid);
> +			pid_t pid;
> +
> +			pid = get_free_pid();
> +			if (pid < 0)
> +				break;
> +			helper = lookup_create_item(pid);
>  			if (helper == NULL)
>  				return -1;
>  
>