Re: [RFC] Signaling overhead on RT tasks is causing RCU stall

[Peter Zijlstra]

On Fri, Jul 05, 2024 at 09:56:23AM +0200, Radoslaw Zielonek wrote:
> Hello,
> 
> I'm working on syzbot bug: rcu detected stall in validate_mm
> https://syzkaller.appspot.com/bug?extid=a941018a091f1a1f9546.
> I have analyzed this issue and here is what I found:
> 
> When too many signals are sent to the RT task, the overhead becomes very high.
> The task cannot perform its job and as a consquenece the rt_runtime (0.95s)
> is not reached even after hundreds of seconds.

I'm having trouble parsing this. What overhead becomes high? Is the task
spending time in-kernel? Because if the task is spending time in-user
handling all its signals, it should accumulate runtime just fine.

That is, your analysis seems to leave out / gloss over the important
bit.