linux-kernel - Re: [PATCH v3 3/3] sched_ext: Guarantee rq lock on scx_bpf_cpu

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Message-ID: <y23etey3foin5nrxgj6e4g373b3ap6oxqa5rrvuvwyus3umw5s@bgh3d6uuga5t>
Date: Mon, 11 Aug 2025 15:35:05 +0100
From: Jake Hillion <jake@...lion.co.uk>
To: Andrea Righi <arighi@...dia.com>
Cc: Tejun Heo <tj@...nel.org>, Christian Loehle <christian.loehle@....com>, 
	void@...ifault.com, linux-kernel@...r.kernel.org, sched-ext@...ts.linux.dev, 
	changwoo@...lia.com, hodgesd@...a.com, mingo@...hat.com, peterz@...radead.org
Subject: Re: [PATCH v3 3/3] sched_ext: Guarantee rq lock on scx_bpf_cpu_rq()

On Sun, Aug 10, 2025 at 12:52:53PM +0200, Andrea Righi wrote:
> Yeah, this is not nice, but they would be still broken though, in PATCH 1/3
> we force schedulers to check for NULL and, if they don't, the verifier
> won't be happy, so this already breaks existing binaries.

I ran some testing on the sched_ext for-next branch, and scx_cosmos is
breaking in cosmos_init including the latest changes. I believe it kicks
off a timer in init, which indirectly calls
`scx_bpf_cpu_rq(cpu)->curr->flags & PF_IDLE`. This should be NULL
checked, but old binaries breaking is pretty inconvenient for new users.

As Andrea says, this is the already merged patch triggering this.

Thanks,
Jake.