Re: [PATCH v15 6/8] blk-mq: prevent offlining hk CPUs with associated online isolated CPUs

[Aaron Tomlin]

On Tue, Jul 21, 2026 at 04:19:26PM +0200, Marco Crivellari wrote:
> Hi,
> 
> On Fri, May 22, 2026 at 1:30 AM Aaron Tomlin <atomlin@xxxxxxxxxxx> wrote:
> > [...]
> >  static bool blk_mq_hctx_has_online_cpu(struct blk_mq_hw_ctx *hctx,
> >                 unsigned int this_cpu)
> >  {
> > @@ -3771,6 +3821,11 @@ static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node)
> >                         struct blk_mq_hw_ctx, cpuhp_online);
> >         int ret = 0;
> >
> > +       if (housekeeping_enabled(HK_TYPE_IO_QUEUE)) {
> > +               if (!blk_mq_hctx_can_offline_hk_cpu(hctx, cpu))
> > +                       return -EINVAL;
> > +       }
> > +
> >         if (!hctx->nr_ctx || blk_mq_hctx_has_online_cpu(hctx, cpu))
> >                 return 0;
> 
> I noticed the existing `if` returns 0, while the added code returns
> -EINVAL. I'm wondering if this will prevent the system from suspending
> because of the -EINVAL error.
> Should ` !cpuhp_tasks_frozen` be added to the if statement?
> 
> eg.
> 
> if (housekeeping_enabled(HK_TYPE_IO_QUEUE) && !cpuhp_tasks_frozen) {
>     if (!blk_mq_hctx_can_offline_hk_cpu(hctx, cpu))
>         return -EINVAL;
> }
> 
> Or maybe just handling this inside blk_mq_hctx_can_offline_hk_cpu()
> returning true.
> 
> Does it make sense?

Hi Marco,

Absolutely!

During system suspend/hibernation I/O is quiesced, and all CPUs are being
taken down for system sleep. Returning -EINVAL breaks system power
management. Offlining must be allowed to proceed.

Yes, we should test for cpuhp_tasks_frozen in
blk_mq_hctx_can_offline_hk_cpu().


Kind regards,
-- 
Aaron Tomlin