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Date: Wed, 5 Nov 2014 12:54:23 +0100
From: Mateusz Guzik <mguzik@...hat.com>
To: Chen Hanxiao <chenhanxiao@...fujitsu.com>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>,
Serge Hallyn <serge.hallyn@...ntu.com>,
Oleg Nesterov <oleg@...hat.com>,
containers@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org, David Howells <dhowells@...hat.com>,
Richard Weinberger <richard.weinberger@...il.com>,
Pavel Emelyanov <xemul@...allels.com>,
Vasiliy Kulikov <segooon@...il.com>
Subject: Re: [PATCH 1/2v6] procfs: show hierarchy of pid namespace
On Wed, Nov 05, 2014 at 06:41:54PM +0800, Chen Hanxiao wrote:
> +static void free_pidns_list(struct list_head *head)
> +{
> + struct pidns_list *tmp, *pos;
> +
> + list_for_each_entry_safe(pos, tmp, head, list) {
> + list_del(&pos->list);
Any need for this one? stuff is freed anyway...
> + put_pid(pos->pid);
> + kfree(pos);
> + }
> +}
> +
> +static int
> +pidns_list_add(struct pid *pid, struct list_head *list_head)
> +{
> + struct pidns_list *ent;
> +
> + ent = kmalloc(sizeof(*ent), GFP_KERNEL);
> + if (!ent)
> + return -ENOMEM;
> +
> + ent->pid = pid;
> + list_add_tail(&ent->list, list_head);
> +
> + return 0;
> +}
> +
> +static int
> +pidns_list_filter(struct list_head *pidns_pid_list,
> + struct list_head *pidns_pid_tree)
> +{
> + struct pidns_list *pos, *pos_t;
> + struct pid_namespace *ns0, *ns1;
> + struct pid *pid0, *pid1;
> + int rc, flag = 0;
> +
> + /*
> + * screen pids with relationship
> + * in pidns_pid_list, we may add pids like:
> + * ns0 ns1 ns2
> + * pid1->pid2->pid3
> + * we should screen pid1, pid2 and keep pid3
> + */
> + list_for_each_entry(pos, pidns_pid_list, list) {
> + list_for_each_entry(pos_t, pidns_pid_list, list) {
> + flag = 0;
> + pid0 = pos->pid;
> + pid1 = pos_t->pid;
> + ns0 = pid0->numbers[pid0->level].ns;
> + ns1 = pid1->numbers[pid1->level].ns;
> + if (pos->pid->level < pos_t->pid->level)
> + for (; ns1 != NULL; ns1 = ns1->parent)
> + if (ns0 == ns1) {
> + flag = 1;
> + break;
> + }
> + /* a redundant pid found */
> + if (flag == 1)
> + break;
> + }
> +
> + if (flag == 0) {
> + rcu_read_lock();
> + get_pid(pos->pid);
> + rcu_read_unlock();
At this point you should have a valid reference for pid, so rcu should
not matter.
> + rc = pidns_list_add(pos->pid, pidns_pid_tree);
> + if (rc) {
> + put_pid(pos->pid);
> + goto out;
> + }
'}' is misindented. Also 'out' is not a good label if it used solely for
cleanup on error. 'out_err', 'fail' or something woud be better.
> + }
> + }
> +
> + /*
> + * Now all usefull stuffs are in pidns_pid_tree,
> + * free pidns_pid_list
> + */
> + free_pidns_list(pidns_pid_list);
> +
> + return 0;
> +
> +out:
> + free_pidns_list(pidns_pid_tree);
> + return rc;
> +}
> +
> +/*
> + * collect pids and stored in pidns_pid_list,
> + * then remove duplicated ones,
> + * add the rest to pidns_pid_tree
> + */
> +static int proc_pidns_list_refresh(struct pid_namespace *curr_ns,
> + struct list_head *pidns_pid_list,
> + struct list_head *pidns_pid_tree)
> +{
> + struct pid *pid;
> + int new_nr, nr = 0;
> + int rc;
> +
> + /* collect pids in current namespace */
> + while (nr < PID_MAX_LIMIT) {
> + rcu_read_lock();
> + pid = find_ge_pid(nr, curr_ns);
> + if (pid) {
> + new_nr = pid_vnr(pid);
> + if (!is_child_reaper(pid)) {
> + nr = new_nr + 1;
> + rcu_read_unlock();
> + continue;
> + }
> + get_pid(pid);
> + rcu_read_unlock();
> + rc = pidns_list_add(pid, pidns_pid_list);
> + if (rc) {
> + put_pid(pid);
> + goto out;
> + }
> + } else {
> + rcu_read_unlock();
> + break;
> + }
> + nr = new_nr + 1;
> + }
> +
Would be beneficial to reorganize this loop. Handle shorter case (!pid)
first.
I consulted Dr. Grep and it told me about delayed_put_pid, so I guess
pid itself is not going to be freed in the meantime, but this still
seems fishy.
> + /*
> + * Only one pid found as the child reaper,
> + * so current pid namespace do not have sub-namespace,
> + * return 0 directly.
> + */
> + if (list_is_singular(pidns_pid_list)) {
> + rc = 0;
> + goto out;
> + }
> +
> + /*
> + * screen duplicate pids from pidns_pid_list
> + * and form a new list pidns_pid_tree.
> + */
> + rc = pidns_list_filter(pidns_pid_list, pidns_pid_tree);
> + if (rc)
> + goto out;
> +
> + return 0;
> +
> +out:
> + free_pidns_list(pidns_pid_list);
> + return rc;
> +}
> +
> +static int nslist_proc_show(struct seq_file *m, void *v)
> +{
> + struct pidns_list *pos;
> + struct pid_namespace *ns, *curr_ns;
> + struct pid *pid;
> + char pid_buf[16];
> + int i, rc;
> +
> + LIST_HEAD(pidns_pid_list);
> + LIST_HEAD(pidns_pid_tree);
> +
> + curr_ns = task_active_pid_ns(current);
> +
> + rc = proc_pidns_list_refresh(curr_ns, &pidns_pid_list, &pidns_pid_tree);
> + if (rc)
> + return rc;
> +
> + /* print pid namespace's hierarchy */
> + list_for_each_entry(pos, &pidns_pid_tree, list) {
> + pid = pos->pid;
> + for (i = curr_ns->level + 1; i <= pid->level; i++) {
> + ns = pid->numbers[i].ns;
> + /* show PID '1' in specific pid ns */
> + snprintf(pid_buf, 16, "%u",
> + pid_vnr(find_pid_ns(1, ns)));
> + seq_printf(m, "%s ", pid_buf);
> + }
> +
> + seq_putc(m, '\n');
> + }
> +
> + free_pidns_list(&pidns_pid_tree);
> +
> + return 0;
> +}
> +
> +static int nslist_proc_open(struct inode *inode, struct file *file)
> +{
> + return single_open(file, nslist_proc_show, NULL);
> +}
> +
> +static const struct file_operations proc_nspid_nslist_fops = {
> + .open = nslist_proc_open,
> + .read = seq_read,
> + .llseek = seq_lseek,
> + .release = single_release,
> +};
> +
> +static int __init pidns_hierarchy_init(void)
> +{
> + proc_create(NS_HIERARCHY, S_IWUGO,
> + NULL, &proc_nspid_nslist_fops);
> +
> + return 0;
> +}
> +fs_initcall(pidns_hierarchy_init);
> --
> 1.9.3
>
--
Mateusz Guzik
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