[RFC 06/10] Reclaim memory from blocked kernel stacks

[Peter Zijlstra]

On Mon, Aug 31, 2026 at 08:55:09AM +0200, Sebastian Andrzej Siewior wrote:
> (stack tracer running)
>         Depth    Size   Location    (60 entries)
>         -----    ----   --------
>   0)     8176      48   __css_rstat_updated+0x9/0x150
>   1)     8128       8   __cgroup_account_cputime+0x2f/0x50
>   2)     8120      48   update_se+0x10c/0x1b0
>   3)     8072      48   update_curr+0x31/0x180
>   4)     8024      56   put_prev_entity+0x153/0x1f0
>   5)     7968     136   pick_next_task_fair+0x684/0x8e0
>   6)     7832     120   __schedule+0x1ca/0x1130
>   7)     7712       8   preempt_schedule_irq+0x38/0x60
>   8)     7704      72   irqentry_exit+0x148/0x6b0
>   9)     7632     136   asm_sysvec_apic_timer_interrupt+0x1a/0x20
>  10)     7496     240   HUF_compress1X_usingCTable_internal_bmi2+0x12d2/0x1c40

> 
> Does this stack tracer distinguish between the kernel-stack and
> IRQ-stack? I would expect asm_sysvec_apic_timer_interrupt() on the
> IRQ-stack and not adding weight to the kernel stack.

This is the return from interrupt path, irqentry_exit() is right after
we switch back from the IRQ stack and are back on the task stack. We
have to be, in order to schedule the task and all that.