Re: [RFC PATCH] PM: Optionally block user fork during freeze to improve performance

[zhangzihuan <zhangzihuan@kylinos.cn>]

Hi Peter,
Thanks a lot for the feedback!

在 2025/6/6 16:22, Peter Zijlstra 写道:
> This isn't blocking fork(), this is failing fork(). Huge difference.
> Also problematic, because -EBUSY is not a recognised return value of
> fork(). As such, no existing software will adequately handle it.
>  I completely agree there's a significant difference between failing 
> and blocking fork().
The intent was to prevent late-created user tasks from interfering with 
the freezing process, but you're right: returning -EBUSY is not valid 
for fork(), and existing user-space programs wouldn't expect or handle 
that properly.
As a next step, I'm considering switching to a blocking mechanism 
instead — that is, have user fork() temporarily sleep if it's attempted 
during the freeze window. That should avoid breaking user-space 
expectations while still helping maintain freeze stability.
Would that be more acceptable?
Thanks again for the insight,
Zihuan Zhang