[PATCH 1/2] introduce the walk_process_tree() helper

Pavel Tikhomirov
2017-01-30T15:24:39Z

From: Oleg Nesterov <oleg@redhat.com>

Add the new helper to walk the process tree, the next patch adds a user.
Note that it visits the group leaders only, proc_visitor can do
for_each_thread itself or we can trivially extend walk_process_tree() to
do this.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
---
include/linux/sched.h | 3 +++
kernel/fork.c | 32 ++++++++++++++++++++++++++++++++
2 files changed, 35 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index ad3ec9e..7f8ab91 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3067,6 +3067,9 @@ extern bool current_is_single_threaded(void);
#define for_each_process_thread(p, t) \
for_each_process(p) for_each_thread(p, t)

+typedef int (*proc_visitor)(struct task_struct *p, void *data);
+void walk_process_tree(struct task_struct *top, proc_visitor, void *);
+
static inline int get_nr_threads(struct task_struct *tsk)
{
return tsk->signal->nr_threads;
diff --git a/kernel/fork.c b/kernel/fork.c
index 11c5c8a..135b7a4 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2053,6 +2053,38 @@ SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
}
#endif

+void walk_process_tree(struct task_struct *top, proc_visitor visitor, void *data)
+{
+ struct task_struct *leader, *parent, *child;
+ int res;
+
+ read_lock(&tasklist_lock);
+ leader = top = top->group_leader;
+down:
+ for_each_thread(leader, parent) {
+ list_for_each_entry(child, &parent->children, sibling) {
+ res = visitor(child, data);
+ if (res) {
+ if (res < 0)
+ goto out;
+ leader = child;
+ goto down;
+ }
+up:
+ ;
+ }
+ }
+
+ if (leader != top) {
+ child = leader;
+ parent = child->real_parent;
+ leader = parent->group_leader;
+ goto up;
+ }
+out:
+ read_unlock(&tasklist_lock);
+}
+
#ifndef ARCH_MIN_MMSTRUCT_ALIGN
#define ARCH_MIN_MMSTRUCT_ALIGN 0
#endif
--
2.9.3