linux-kernel - Re: [PATCH 0/8] tracing vs rcu vs nmi

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Message-ID: <20200212105646.GA4017@willie-the-truck>
Date:   Wed, 12 Feb 2020 10:56:46 +0000
From:   Will Deacon <will@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        rostedt@...dmis.org, james.morse@....com, catalin.marinas@....com,
        mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, paulmck@...nel.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com
Subject: Re: [PATCH 0/8] tracing vs rcu vs nmi

On Wed, Feb 12, 2020 at 11:01:06AM +0100, Peter Zijlstra wrote:
> On Wed, Feb 12, 2020 at 10:32:10AM +0100, Peter Zijlstra wrote:
> > Hi all,
> > 
> > These here patches are the result of Mathieu and Steve trying to get commit
> > 865e63b04e9b2 ("tracing: Add back in rcu_irq_enter/exit_irqson() for rcuidle
> > tracepoints") reverted again.
> > 
> > One of the things discovered is that tracing MUST NOT happen before nmi_enter()
> > or after nmi_exit(). I've only fixed x86, but quickly gone through other
> > architectures and there is definitely more stuff to be fixed (simply grep for
> > nmi_enter in your arch).
> 
> For ARM64:
> 
>  - apei_claim_sea()
>  - __sdei_handler()
>  - do_serror()
>  - debug_exception_enter() / do_debug_exception()
> 
> all look dodgy.

Hmm, so looks like we need to spinkle some 'notrace' annotations around
these. Are there are scenarios where you would want NOKPROBE_SYMBOL() but
*not* 'notrace'? We've already got the former for the debug exception
handlers and we probably (?) want it for the SDEI stuff too...

Will