From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932615Ab2ASRry (ORCPT ); Thu, 19 Jan 2012 12:47:54 -0500 Received: from mail-bk0-f46.google.com ([209.85.214.46]:51526 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932129Ab2ASRrw (ORCPT ); Thu, 19 Jan 2012 12:47:52 -0500 Date: Thu, 19 Jan 2012 21:47:42 +0400 From: Cyrill Gorcunov To: Oleg Nesterov , Andrew Morton Cc: KOSAKI Motohiro , LKML , Pavel Emelyanov , Serge Hallyn , KAMEZAWA Hiroyuki , Tejun Heo , Andrew Vagin , Vasiliy Kulikov Subject: Re: [PATCH] fs, proc: Introduce /proc//task//children entry v7 Message-ID: <20120119174742.GD32568@moon> References: <20120119155112.GF31379@moon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120119155112.GF31379@moon> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 19, 2012 at 07:51:12PM +0400, Cyrill Gorcunov wrote: > If it's needed I can wrap all this with CONFIG_CHECKPOINT_RESTORE, should I? > > --- Oleg, if only I'm not missing something obvious you meant handling like below? Cyrill --- From: Cyrill Gorcunov Subject: fs, proc: Introduce /proc//task//children entry v8 When we do checkpoint of a task we need to know the list of children the task, has but there is no easy and fast way to generate reverse parent->children chain from arbitrary (while a parent pid is provided in "PPid" field of /proc//status). So instead of walking over all pids in the system (creating one big process tree in memory, just to figure out which children a task has) -- we add explicit /proc//task//children entry, because the kernel already has this kind of information but it is not yet exported. This is a first level children, not the whole process tree. v2: - Kame suggested to use a separated /proc//children entry instead of poking /proc//status - Andew suggested to use rcu facility instead of locking tasklist_lock - Tejun pointed that non-seekable seq file might not be enough for tasks with large number of children v3: - To be on a safe side use %lu format for pid_t printing v4: - New line get printed when sequence ends not at seq->stop, a nit pointed by Tejun - Documentation update - tasklist_lock is back, Oleg pointed that ->children list is actually not rcu-safe v5: - Oleg suggested to make /proc//task//children instead of global /proc//children, which eliminates hardness related to threads and children migration, and allows patch to be a way simplier. v6: - Drop ptrace_may_access tests, pids are can be found anyway so nothing to protect here. - Update comments and docs, pointed by Oleg. v7: - Use get_pid over proc-pid directly, to simplify code, pointed by Oleg. v8: - Obtain a starting pid from the proc's inode directly. Signed-off-by: Cyrill Gorcunov Cc: Andrew Morton Cc: Pavel Emelyanov Cc: Serge Hallyn Cc: KAMEZAWA Hiroyuki Cc: Oleg Nesterov --- Documentation/filesystems/proc.txt | 18 +++++ fs/proc/array.c | 128 +++++++++++++++++++++++++++++++++++++ fs/proc/base.c | 1 fs/proc/internal.h | 1 4 files changed, 148 insertions(+) Index: linux-2.6.git/Documentation/filesystems/proc.txt =================================================================== --- linux-2.6.git.orig/Documentation/filesystems/proc.txt +++ linux-2.6.git/Documentation/filesystems/proc.txt @@ -40,6 +40,7 @@ Table of Contents 3.4 /proc//coredump_filter - Core dump filtering settings 3.5 /proc//mountinfo - Information about mounts 3.6 /proc//comm & /proc//task//comm + 3.7 /proc//task//children - Information about task children 4 Configuring procfs 4.1 Mount options @@ -1549,6 +1550,23 @@ then the kernel's TASK_COMM_LEN (current comm value. +3.7 /proc//task//children - Information about task children +------------------------------------------------------------------------- +This file provides a fast way to retrieve first level children pids +of a task pointed by / pair. The format is a space separated +stream of pids. + +Note the "first level" here -- if a child has own children they will +not be listed here, one needs to read /proc//task//children +to obtain the descendants. + +Since this interface is intended to be fast and cheap it doesn't +guarantee to provide precise results and some children might be +skipped, especially if they've exited right after we printed their +pids, so one need to either stop or freeze processes being inspected +if precise results are needed. + + ------------------------------------------------------------------------------ Configuring procfs ------------------------------------------------------------------------------ Index: linux-2.6.git/fs/proc/array.c =================================================================== --- linux-2.6.git.orig/fs/proc/array.c +++ linux-2.6.git/fs/proc/array.c @@ -547,3 +547,131 @@ int proc_pid_statm(struct seq_file *m, s return 0; } + +struct proc_pid_children_iter { + struct pid_namespace *pid_ns; + struct pid *parent_pid; +}; + +static struct pid * +get_children_pid(struct inode *inode, struct pid *pid_prev, loff_t pos) +{ + struct task_struct *start, *task; + struct pid *pid = NULL; + + read_lock(&tasklist_lock); + + start = pid_task(proc_pid(inode), PIDTYPE_PID); + if (!start) + goto out; + + /* + * Lets try to continue searching first, this gives + * us significant speedup on children-rich processes. + */ + if (pid_prev) { + task = pid_task(pid_prev, PIDTYPE_PID); + if (task && task->real_parent == start && + !(list_empty(&task->sibling))) { + if (list_is_last(&task->sibling, &start->children)) + goto out; + task = list_first_entry(&task->sibling, + struct task_struct, sibling); + pid = get_pid(task_pid(task)); + goto out; + } + } + + /* + * Slow search case. + * + * We might miss some children here if children + * are exited while we were not holding the lock, + * but it was never promised to be accurate that + * much. + * + * "Just suppose that the parent sleeps, but N children + * exit after we printed their tids. Now the slow paths + * skips N extra children, we miss N tasks." (c) + * + * So one need to stop or freeze the leader and all + * its children to get a precise result. + */ + list_for_each_entry(task, &start->children, sibling) { + if (pos-- == 0) { + pid = get_pid(task_pid(task)); + break; + } + } + +out: + read_unlock(&tasklist_lock); + return pid; +} + +static int children_seq_show(struct seq_file *seq, void *v) +{ + struct inode *inode = seq->private; + unsigned long pid; + + pid = (unsigned long)pid_nr_ns(v, inode->i_sb->s_fs_info); + return seq_printf(seq, " %lu", pid); +} + +static void *children_seq_start(struct seq_file *seq, loff_t *pos) +{ + return get_children_pid(seq->private, NULL, *pos); +} + +static void *children_seq_next(struct seq_file *seq, void *v, loff_t *pos) +{ + struct pid *pid = NULL; + + pid = get_children_pid(seq->private, v, *pos + 1); + if (!pid) + seq_printf(seq, "\n"); + put_pid(v); + + ++*pos; + return pid; +} + +static void children_seq_stop(struct seq_file *seq, void *v) +{ + put_pid(v); +} + +static const struct seq_operations children_seq_ops = { + .start = children_seq_start, + .next = children_seq_next, + .stop = children_seq_stop, + .show = children_seq_show, +}; + +static int children_seq_open(struct inode *inode, struct file *file) +{ + struct seq_file *m; + int ret; + + ret = seq_open(file, &children_seq_ops); + if (ret) + return ret; + + m = file->private_data; + m->private = inode; + + return ret; +} + +int children_seq_release(struct inode *inode, struct file *file) +{ + seq_release(inode, file); + return 0; +} + +const struct file_operations proc_tid_children_operations = { + .open = children_seq_open, + .read = seq_read, + .llseek = seq_lseek, + .release = children_seq_release, +}; Index: linux-2.6.git/fs/proc/base.c =================================================================== --- linux-2.6.git.orig/fs/proc/base.c +++ linux-2.6.git/fs/proc/base.c @@ -3454,6 +3454,7 @@ static const struct pid_entry tid_base_s ONE("stat", S_IRUGO, proc_tid_stat), ONE("statm", S_IRUGO, proc_pid_statm), REG("maps", S_IRUGO, proc_maps_operations), + REG("children", S_IRUGO, proc_tid_children_operations), #ifdef CONFIG_NUMA REG("numa_maps", S_IRUGO, proc_numa_maps_operations), #endif Index: linux-2.6.git/fs/proc/internal.h =================================================================== --- linux-2.6.git.orig/fs/proc/internal.h +++ linux-2.6.git/fs/proc/internal.h @@ -53,6 +53,7 @@ extern int proc_pid_statm(struct seq_fil struct pid *pid, struct task_struct *task); extern loff_t mem_lseek(struct file *file, loff_t offset, int orig); +extern const struct file_operations proc_tid_children_operations; extern const struct file_operations proc_maps_operations; extern const struct file_operations proc_numa_maps_operations; extern const struct file_operations proc_smaps_operations;