Re: [PATCH 04/18] sched/core: Avoid false migration warning for proxy donors

[Peter Zijlstra]

On Tue, Sep 15, 2026 at 07:20:45PM +0200, Andrea Righi wrote:

> > > I'm not sure why we're not hitting this upstream?
> > 
> > I think this can be hit upstream as well. I'll try to create a reproducer.
> 
> And I can reproduce this with the latest tip/master:
> 
>   proxy_migrate_repro: donor blocking on CPU0 with migration disabled
>   proxy_migrate_repro: donor moved from CPU0 to CPU1
>   WARNING: kernel/sched/core.c:3389 at set_task_cpu+0x1d3/0x280
>   ...
>   Call Trace:
>    try_to_wake_up+0x43f/0x780
>    __mutex_unlock_slowpath+0x330/0x540
>    owner_fn+0x9f/0xc0 [proxy_migrate_repro]
>   ...
>   proxy_migrate_repro: donor woke on CPU0, task_cpu=0
>   proxy_migrate_repro: completed
> 
> The reproducer creates a mutex owner on CPU1 and a migration-disabled waiter on
> CPU0. The waiter is proxy-migrated to CPU1 while blocked. When the owner
> releases the mutex, try_to_wake_up() returns the waiter to its pinned CPU0
> through set_task_cpu(), triggering the warning.
> 
> I guess I can send this as a separate fix, it doesn't necessarily need to be in
> this series.

Right, or at the head with a Fixes tag on will do too. Thanks for
checking!