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Date:   Mon, 24 Oct 2022 13:20:57 +0100
From:   Mark Rutland <mark.rutland@arm.com>
To:     Yu Liao <liaoyu15@huawei.com>
Cc:     "Paul E. McKenney" <paulmck@kernel.org>,
        "liwei (GF)" <liwei391@huawei.com>, linux-kernel@vger.kernel.org,
        rcu@vger.kernel.org
Subject: Re: [BUG] possible deadlock in __rcu_irq_enter_check_tick
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On Thu, Oct 20, 2022 at 09:32:35PM +0800, Yu Liao wrote:
> On 2022/10/19 22:14, Mark Rutland wrote:
> > On Tue, Oct 18, 2022 at 03:24:48PM +0100, Mark Rutland wrote:

> > Having a go with v6.1-rc1, placing a kprobe on __rcu_irq_enter_check_tick()
> > causes a recursive exception which triggers the stack overflow detection, so
> > there are bigger problems here, and we'll need to do some further rework of the
> > arm64 entry code. FWIW, x86-64 seems fine.
> > 
> > I have a vague recollection that that there was something (some part kprobes,
> > perhaps) that didn't like being called in NMI context, which is why debug
> > exceptions aren't accounted as true NMIs (but get most of the same treatment).
> > 
> > I'll have to dig into this a bit more; there are a bunch of subtle interactions
> > in this area, and I don't want to put a band-aid over this without fully
> > understanding the implications.
> > 
> > Once we've figured that out for mainline, we can figure out what needs to go to
> > stable.
> > 
> > Yu, were you particularly interested in tracing __rcu_irq_enter_check_tick(),
> > or did you stumble upon this by other means?

> Oh，This was found with the help of the kernel fuzzer syzkaller.

Thanks for confirming!

I've also been testing with Syzkaller, but it looks like I haven't had KPROBES
enabled due to deselecting MODULE support, which explains how I've missed this
until now. :/

I'll go fiddle with moy configs.

Thanks,
Mark.