linux-kernel - [PATCH] bpf: task_group_seq_get_next: cleanup the usage of next

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Message-ID: <20230821150909.GA2431@redhat.com>
Date:   Mon, 21 Aug 2023 17:09:09 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Yonghong Song <yhs@...com>, Kui-Feng Lee <kuifeng@...com>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Martin KaFai Lau <martin.lau@...nel.org>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] bpf: task_group_seq_get_next: cleanup the usage of
 next_thread()

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@...hat.com>
---
 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);
-- 
2.25.1.362.g51ebf55