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.

Fernand, please correct me if I got the explanations wrong.

Thanks! Holger

[1] https://bugs.gentoo.org/968116 starting at #8