On 8/25/23 9:19 AM, Oleg Nesterov wrote:
1. find_pid_ns() + get_pid_task() under rcu_read_lock() guarantees that we
can safely iterate the task->thread_group list. Even if this task exits
right after get_pid_task() (or goto retry) and pid_alive() returns 0.
Kill the unnecessary pid_alive() check.
2. next_thread() simply can't return NULL, kill the bogus "if (!next_task)"
check.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
__unhash_process() tries to detach_pid() (pid_alive() may become false)
and ist_del_rcu(&p->thread_group). So yes, next_thread() should be safe
to grab next_task since &task->thread_group is rcu protected. So
Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx>
---
kernel/bpf/task_iter.c | 7 -------
1 file changed, 7 deletions(-)
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index c4ab9d6cdbe9..4d1125108014 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -75,15 +75,8 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm
return NULL;
retry:
- if (!pid_alive(task)) {
- put_task_struct(task);
- return NULL;
- }
-
next_task = next_thread(task);
put_task_struct(task);
- if (!next_task)
- return NULL;
saved_tid = *tid;
*tid = __task_pid_nr_ns(next_task, PIDTYPE_PID, common->ns);
