On 11/16/23 4:54 AM, Oleg Nesterov wrote:
On 11/15, Yonghong Song wrote:
On 11/14/23 11:32 AM, Oleg Nesterov wrote:
Compile tested.
Every lockless usage of next_thread() was wrong, bpf/task_iter.c is
the last user and is no exception.
It would be great if you can give more information in the commit message
about why the usage of next_thread() is wrong in bpf/task_iter.c.
I tried to explain the problems in the changelogs:
1/3:
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.
2/3:
bpf_iter_task_next() can loop forever, "kit->pos == kit->task" can never
happen if kit->pos execs.
IIUC, some information is presented in :
https://lore.kernel.org/all/20230824143112.GA31208@xxxxxxxxxx/
Yes, Linus and Eric suggest to simply kill next_thread(). I am not
sure, this needs another discussion.
But as for bpf/task_iter.c... Even _if_ the usage was correct, this
code simply doesn't need the "circular" next_thread(), NULL at the
end simplifies the code.
Also, please add 'bpf' in the subject tag ([PATCH bpf 0/3]) to
make it clear the patch should be applied to bpf tree.
OK, will do next time. Or should I resend this series with 'bpf'
in the subject tag?
There is no need then. We can wait for maintainers who may or
may not have additional requests.
Thanks,
Oleg.
