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Date: Tue, 17 Feb 2015 11:20:24 +0300
From: Andrey Vagin <avagin@...nvz.org>
To: linux-kernel@...r.kernel.org
Cc: linux-api@...r.kernel.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>, Andrey Vagin <avagin@...nvz.org>
Subject: [PATCH 5/7] kernel: add ability to iterate children of a specified task
The interface is similar with the tgid iterator. It is used in
procfs and it will be used in task_diag.
Signed-off-by: Andrey Vagin <avagin@...nvz.org>
---
fs/proc/array.c | 58 +++++++++++++------------------------------------
include/linux/proc_fs.h | 6 +++++
kernel/pid.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 76 insertions(+), 43 deletions(-)
diff --git a/fs/proc/array.c b/fs/proc/array.c
index bd117d0..7197c6a 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -579,54 +579,26 @@ get_children_pid(struct inode *inode, struct pid *pid_prev, loff_t pos)
{
struct task_struct *start, *task;
struct pid *pid = NULL;
+ struct child_iter iter;
- read_lock(&tasklist_lock);
-
- start = pid_task(proc_pid(inode), PIDTYPE_PID);
+ start = get_proc_task(inode);
if (!start)
- goto out;
+ return NULL;
- /*
- * 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;
- }
- }
+ if (pid_prev)
+ task = get_pid_task(pid_prev, PIDTYPE_PID);
+ else
+ task = NULL;
- /*
- * 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;
- }
- }
+ iter.parent = start;
+ iter.task = task;
+ iter.pos = pos;
+
+ iter = next_child(iter);
-out:
- read_unlock(&tasklist_lock);
+ put_task_struct(start);
+ if (iter.task)
+ pid = get_pid(task_pid(iter.task));
return pid;
}
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 136b6ed..eba98bc 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -89,4 +89,10 @@ struct tgid_iter {
struct tgid_iter next_tgid(struct pid_namespace *ns, struct tgid_iter iter);
+struct child_iter {
+ struct task_struct *task, *parent;
+ unsigned int pos;
+};
+
+struct child_iter next_child(struct child_iter iter);
#endif /* _LINUX_PROC_FS_H */
diff --git a/kernel/pid.c b/kernel/pid.c
index 082307a..6e3e42a 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -606,6 +606,61 @@ retry:
return iter;
}
+struct child_iter next_child(struct child_iter iter)
+{
+ struct task_struct *task;
+ loff_t pos = iter.pos;
+
+ read_lock(&tasklist_lock);
+
+ /*
+ * Lets try to continue searching first, this gives
+ * us significant speedup on children-rich processes.
+ */
+ if (iter.task) {
+ task = iter.task;
+ if (task && task->real_parent == iter.parent &&
+ !(list_empty(&task->sibling))) {
+ if (list_is_last(&task->sibling, &iter.parent->children)) {
+ task = NULL;
+ goto out;
+ }
+ task = list_first_entry(&task->sibling,
+ struct task_struct, sibling);
+ 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, &iter.parent->children, sibling) {
+ if (pos-- == 0)
+ goto out;
+ }
+ task = NULL;
+out:
+ if (iter.task)
+ put_task_struct(iter.task);
+ if (task)
+ get_task_struct(task);
+ iter.task = task;
+ read_unlock(&tasklist_lock);
+ return iter;
+}
+
/*
* The pid hash table is scaled according to the amount of memory in the
* machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or
--
2.1.0
--
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