linux-kernel - [PATCH 5/6] bpf: task_group_seq_get_next: simplify the "next tid" logic

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Message-ID: <20230825161954.GA16886@redhat.com>
Date:   Fri, 25 Aug 2023 18:19:54 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Yonghong Song <yhs@...com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kui-Feng Lee <kuifeng@...com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...nel.org>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 5/6] bpf: task_group_seq_get_next: simplify the "next tid"
 logic

Kill saved_tid. It looks ugly to update *tid and then restore the
previous value if __task_pid_nr_ns() returns 0. Change this code
to update *tid and common->pid_visiting once before return.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/bpf/task_iter.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index f51f476ec679..7473068ed313 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -37,7 +37,7 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm
 {
 	struct task_struct *task;
 	struct pid *pid;
-	u32 saved_tid;
+	u32 next_tid;
 
 	if (!*tid) {
 		/* The first time, the iterator calls this function. */
@@ -70,21 +70,18 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm
 retry:
 	task = next_thread(task);
 
-	saved_tid = *tid;
-	*tid = __task_pid_nr_ns(task, PIDTYPE_PID, common->ns);
-	if (!*tid || *tid == common->pid) {
+	next_tid = __task_pid_nr_ns(task, PIDTYPE_PID, common->ns);
+	if (!next_tid || next_tid == common->pid) {
 		/* Run out of tasks of a process.  The tasks of a
 		 * thread_group are linked as circular linked list.
 		 */
-		*tid = saved_tid;
 		return NULL;
 	}
 
-	common->pid_visiting = *tid;
-
 	if (skip_if_dup_files && task->files == task->group_leader->files)
 		goto retry;
 
+	*tid = common->pid_visiting = next_tid;
 	get_task_struct(task);
 	return task;
 }
-- 
2.25.1.362.g51ebf55