| Message ID | 20231114163211.GA874@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | bpf: kernel/bpf/task_iter.c: don't abuse next_thread() | expand |
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. IIUC, some information is presented in : https://lore.kernel.org/all/20230824143112.GA31208@redhat.com/ Also, please add 'bpf' in the subject tag ([PATCH bpf 0/3]) to make it clear the patch should be applied to bpf tree. > > Oleg. > --- > > kernel/bpf/task_iter.c | 29 +++++++++++------------------ > 1 file changed, 11 insertions(+), 18 deletions(-) >
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@redhat.com/ 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? Thanks, Oleg.
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@redhat.com/ > 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. >
Hello: This series was applied to bpf/bpf-next.git (master) by Alexei Starovoitov <ast@kernel.org>: On Tue, 14 Nov 2023 17:32:11 +0100 you wrote: > Compile tested. > > Every lockless usage of next_thread() was wrong, bpf/task_iter.c is > the last user and is no exception. > > Oleg. > > [...] Here is the summary with links: - [1/3] bpf: task_group_seq_get_next: use __next_thread() rather than next_thread() https://git.kernel.org/bpf/bpf-next/c/2d1618054f25 - [2/3] bpf: bpf_iter_task_next: use __next_thread() rather than next_thread() https://git.kernel.org/bpf/bpf-next/c/5a34f9dabd9a - [3/3] bpf: bpf_iter_task_next: use next_task(kit->task) rather than next_task(kit->pos) https://git.kernel.org/bpf/bpf-next/c/ac8148d957f5 You are awesome, thank you!