Commit 2d161805 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Alexei Starovoitov
Browse files

bpf: task_group_seq_get_next: use __next_thread() rather than next_thread() 



Lockless use of next_thread() should be avoided, kernel/bpf/task_iter.c
is the last user and the usage is wrong.

task_group_seq_get_next() can return the group leader twice if it races
with mt-thread exec which changes the group->leader's pid.

Change the main loop to use __next_thread(), kill "next_tid == common->pid"
check.

__next_thread() can't loop forever, we can also change this code to retry
if next_tid == 0.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarYonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20231114163234.GA890@redhat.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 16b3129e

kernel/bpf/task_iter.c

+5 −7
Original line number Diff line number Diff line
@@ -70,15 +70,13 @@ static struct task_struct *task_group_seq_get_next(struct bpf_iter_seq_task_comm 
		return NULL;



retry:

	task = next_thread(task);

	task = __next_thread(task);

	if (!task)

		return NULL;



	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.

		 */

		return NULL;

	}

	if (!next_tid)

		goto retry;



	if (skip_if_dup_files && task->files == task->group_leader->files)

		goto retry;