Re: Please add 127b90315ca0 ("sched/proxy: Yield the donor task") to 6.12.y / 6.18.y

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

> Hi -
> 
> a Gentoo user recently found that 6.18.2 started to reproducuibly
> crash when building their go toolchain [1].
> 
> Apparently the addition of "sched/fair: Forfeit vruntime on yield"
> (mainline 79104becf42b) can result in the infamous NULL returned from
> pick_eevdf(), which is not supposed to happen.
> 
> It turned out that the mentioned commit triggered a bug related
> to the recently added proxy execution feature, which was already
> fixed in mainline by "sched/proxy: Yield the donor task"
> (127b90315ca0), though not marked for stable.
> 
> Applying this to 6.18.2/.3-rc1 (and probably 6.12 as well)
> has reproducibly fixed the problem. A possible reason the crash
> was triggered by the Go runtime could be its specific use of yield(),
> though that's just speculation on my part.
> 
> So please add 127b90315ca0 ("sched/proxy: Yield the donor task")
> to 6.18.y/6.12.y. I know we're already in 6.18.3-rc1, but the
> crasher seems reproducible.

Failed to apply 127b90315ca0 ("sched/proxy: Yield the donor task")
to 6.12.y, because  the 'donor task‘ is a feature of 6.13.

commit af0c8b2bf67b25756f27644936e74fd9a6273bd2
Author: Peter Zijlstra <peterz@infradead.org>
Date:   Wed Oct 9 16:53:40 2024 -0700

    sched: Split scheduler and execution contexts

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2025/12/31