linux-kernel - [PATCH 01/15] proc: pick out a function to iterate task children

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Message-Id: <1460417755-18201-2-git-send-email-avagin@openvz.org>
Date:	Mon, 11 Apr 2016 16:35:41 -0700
From:	Andrey Vagin <avagin@...nvz.org>
To:	linux-kernel@...r.kernel.org
Cc:	Andrey Vagin <avagin@...nvz.org>, Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Roger Luethi <rl@...lgate.ch>, Arnd Bergmann <arnd@...db.de>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	David Ahern <dsahern@...il.com>,
	Andy Lutomirski <luto@...capital.net>,
	Pavel Odintsov <pavel.odintsov@...il.com>
Subject: [PATCH 01/15] proc: pick out a function to iterate task children

This function will be used in task_diag.

Signed-off-by: Andrey Vagin <avagin@...nvz.org>
---
 fs/proc/array.c    | 53 +++++++++++++++++++++++++++++++++--------------------
 fs/proc/internal.h |  3 +++
 2 files changed, 36 insertions(+), 20 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index b6c00ce..3eceab1 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -593,31 +593,25 @@ int proc_pid_statm(struct seq_file *m, struct pid_namespace *ns,
 }
 
 #ifdef CONFIG_PROC_CHILDREN
-static struct pid *
-get_children_pid(struct inode *inode, struct pid *pid_prev, loff_t pos)
+struct task_struct *
+task_next_child(struct task_struct *parent, struct task_struct *prev, unsigned int 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;
+	struct task_struct *task;
 
 	/*
 	 * 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 &&
+	if (prev) {
+		task = prev;
+		if (task && task->real_parent == parent &&
 		    !(list_empty(&task->sibling))) {
-			if (list_is_last(&task->sibling, &start->children))
+			if (list_is_last(&task->sibling, &parent->children)) {
+				task = NULL;
 				goto out;
+			}
 			task = list_first_entry(&task->sibling,
 						struct task_struct, sibling);
-			pid = get_pid(task_pid(task));
 			goto out;
 		}
 	}
@@ -637,12 +631,31 @@ get_children_pid(struct inode *inode, struct pid *pid_prev, loff_t pos)
 	 * 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;
-		}
+	list_for_each_entry(task, &parent->children, sibling) {
+		if (pos-- == 0)
+			goto out;
 	}
+	task = NULL;
+out:
+	return task;
+}
+
+static struct pid *
+get_children_pid(struct inode *inode, struct pid *prev_pid, loff_t pos)
+{
+	struct task_struct *start, *task, *prev;
+	struct pid *pid = NULL;
+
+	read_lock(&tasklist_lock);
+	start = pid_task(proc_pid(inode), PIDTYPE_PID);
+	if (!start)
+		goto out;
+
+	prev = prev_pid ? pid_task(prev_pid, PIDTYPE_PID) : NULL;
+
+	task = task_next_child(start, prev, pos);
+	if (task)
+		pid = get_pid(task_pid(task));
 
 out:
 	read_unlock(&tasklist_lock);
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index aa27810..969e05b 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -303,3 +303,6 @@ extern unsigned long task_statm(struct mm_struct *,
 				unsigned long *, unsigned long *,
 				unsigned long *, unsigned long *);
 extern void task_mem(struct seq_file *, struct mm_struct *);
+
+struct task_struct *
+task_next_child(struct task_struct *parent, struct task_struct *prev, unsigned int pos);
-- 
2.5.5