Re: [PATCH v2 0/2] sched/core: Fix proxy-exec/core-sched interactions

[John Stultz]

On Thu, May 7, 2026 at 3:42 AM Vasily Gorbik <gor@xxxxxxxxxxxxx> wrote:
>
> v1 [1] consisted of a fix for a scheduler corruption where
> try_steal_cookie() could migrate a proxy-exec donor away from the source
> rq while that rq still used it as the active scheduling context.
>
> Prateek pointed out [2] a separate proxy-exec/core-sched issue: after
> pick_next_task() selects a core cookie compatible donor, find_proxy_task()
> can replace the execution context with a mutex owner with a different
> cookie.
>
> This v2 keeps the donor steal fix as patch 1 and adds patch 2 to reject
> mismatched final proxy owners.
>
> The v1 reported the issue reproduced on s390 LPAR, but it seems to be
> easily reproducible with strace test suite "make -j$(nproc) check" on
> any system with SMT, CONFIG_SCHED_CORE=y and CONFIG_SCHED_PROXY_EXEC=y
> enabled, e.g. on x86 KVM with -smp cpus=16,sockets=1,cores=8,threads=2:
>

Vasily! Thank you so much for reporting this and working out fixes
(along with K Prateek!)

Apologies for being slow to reply, I've been under the weather.

I really appreciate this reproducer detail, but I've so far not been
able to trip this issue up (SCHED_CORE=y, SCHED_PROXY_EXEC=y and using
the qemu arguments you included above). Could you mail me your .config
in case something else is needed?

thanks
-john