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

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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: Oleg Nesterov <oleg@redhat.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20231114163234.GA890@redhat.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Oleg Nesterov 2023-11-14 17:32:34 +01:00 committed by Alexei Starovoitov
parent 16b3129e14
commit 2d1618054f
1 changed files with 5 additions and 7 deletions
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12
kernel/bpf/task_iter.c
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@ -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;