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Date: Thu, 19 Mar 2026 17:33:50 +0100
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Boqun Feng <boqun@kernel.org>
Cc: Joel Fernandes <joelagnelf@nvidia.com>, paulmck@kernel.org,
	frederic@kernel.org, neeraj.iitr10@gmail.com, urezki@gmail.com,
	boqun.feng@gmail.com, rcu@vger.kernel.org,
	Kumar Kartikeya Dwivedi <memxor@gmail.com>,
	Tejun Heo <tj@kernel.org>
Subject: Re: Next-level bug in SRCU implementation of RCU Tasks Trace +
 PREEMPT_RT
Message-ID: <20260319163350.c7WuYOM9@linutronix.de>
References: <214fb140-041d-4fd1-8694-658547209b84@paulmck-laptop>
 <3c4c5a29-24ea-492d-aeee-e0d9605b4183@nvidia.com>
 <absesPf-10awctq9@tardis.local>
 <absfZGD3en9TUA1U@tardis.local>
 <absj6rZbyLZY8PPz@tardis.local>
 <da4313b1-9ff5-46e9-b3b7-206dbcb72602@nvidia.com>
 <abs026TUV9oAg_Xy@tardis.local>
 <abtMhd_LVp3uL_pA@tardis.local>
 <20260319090315.Ec_eXAg4@linutronix.de>
 <abwkD0mOdAbD9ENJ@tardis.local>
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In-Reply-To: <abwkD0mOdAbD9ENJ@tardis.local>

On 2026-03-19 09:27:59 [-0700], Boqun Feng wrote:
> On Thu, Mar 19, 2026 at 10:03:15AM +0100, Sebastian Andrzej Siewior wrote:
> > Please just use the queue_delayed_work() with a delay >0.
> > 
> 
> That doesn't work since queue_delayed_work() with a positive delay will
> still acquire timer base lock, and we can have BPF instrument with timer
> base lock held i.e. calling call_srcu() with timer base lock.
> 
> irq_work on the other hand doesn't use any locking.

Could we please restrict BPF somehow so it does roam free? It is
absolutely awful to have irq_work() in call_srcu() just because it
might acquire locks.

> Regards,
> Boqun
> 
Sebastian