Re: [patch 0/4] sched/mmcid: Cure mode transition woes

[Ihor Solodrai <ihor.solodrai@linux.dev>]

On 1/29/26 1:20 PM, Thomas Gleixner wrote:
> Ihor and Shrikanth reported hard lockups which can be tracked back to the recent
> rewrite of the MM_CID management code.
> 
>   1) The from task to CPU ownership transition lacks the intermediate
>      transition mode, which can lead to CID pool exhaustion and a
>      subsequent live lock. That intermediate mode was implemented for the
>      reverse operation already but omitted for this transition as the
>      original analysis missed a few possible scheduling scenarios.
> 
>   2) Weakly ordered architectures can observe inconsistent state which
>      causes them to make the wrong decision. That leads to the same problem
>      as with #1.
> 
> The following series addresses these issue and fixes another albeit harmless
> inconsistent state hickup which was found when analysing the above issues.

Thomas, thank you for addressing this so quickly.

I applied the series as temporary BPF CI specific patches.
I'll report if I notice any relevant issues.

> 
> With these issues addressed the last change optimizes the bitmap
> utilization in the transition modes.
> 
> The series applies on Linus tree and passes the selftests and a thread pool
> emulator which stress tests the ownership transitions.
> 
> Thanks,
> 
> 	tglx
> ---
>  include/linux/rseq_types.h |    7 -
>  kernel/sched/core.c        |  170 +++++++++++++++++++++++++++++----------------
>  kernel/sched/sched.h       |   45 +++++++++--
>  3 files changed, 151 insertions(+), 71 deletions(-)