Re: [patch 00/12] hrtimers: Prevent hrtimer interrupt starvation

[Thomas Gleixner <tglx@kernel.org>]

On Tue, Apr 07 2026 at 16:43, Thomas Gleixner wrote:
> On Tue, Apr 07 2026 at 10:54, Thomas Gleixner wrote:
>> There needs to be some discussion about the scope of backporting. The first
>> patch preventing the stall is obviously a backport candidate. The remaining
>> series can be obviously argued about, but in my opinion it should be
>> backported as well as it prevents stupid or malicious user space from
>> generating tons of pointless timer interrupts.
>
> Peter and me just discussed it over IRC. With the clockevents prevention
> in place, the effect of stupid/malicious code is pretty much affecting
> only the user space task itself. As the timer is forced to expire once
> the clockevent device has been force armed, it won't have other side
> effects as device interrupts or IPIs are not blocked out and in the
> worst case marginally delayed by the high frequency timer interrupt.
>
> Once the task is scheduled out that subsides as there is nothing which
> re-arms the timer anymore.
>
> So we should be fine with backporting the clockevents fix and leave the
> other parts of the series for upstream only. I still need to investigate
> how all of that affects the pending changes vs. TSC deadline timer (and
> similar devices) which are not going to reach that modified clockevents
> code anymore.

It's pretty much the same as the above with the difference that a timer
armed in the past will result in an instantaneous interrupt as the
coupled event devices must provide a less than or equal comparator. So
again the task can only delay itself with hrtimer interrupts.

Thanks,

        tglx