linux-kernel - Re: [patch 4/8] x86/entry: Move irq tracing on syscall entry to C-code

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Message-Id: <AED99B11-8739-450F-932C-EF38C20D44CA@amacapital.net>
Date:   Sun, 1 Mar 2020 06:37:04 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Brian Gerst <brgerst@...il.com>,
        Juergen Gross <JGross@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [patch 4/8] x86/entry: Move irq tracing on syscall entry to C-code



> On Mar 1, 2020, at 2:16 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> Steven Rostedt <rostedt@...dmis.org> writes:
> 
>> On Sat, 29 Feb 2020 11:25:24 -0800
>> Andy Lutomirski <luto@...capital.net> wrote:
>> 
>>>> While the tracer itself seems to handle this correctly, what about
>>>> things like BPF programs which can be attached to tracepoints and
>>>> function trace entries?  
>>> 
>>> I think that everything using the tracing code, including BPF, should
>>> either do its own rcuidle stuff or explicitly not execute if we’re
>>> not in CONTEXT_KERNEL.  That is, we probably need to patch BPF.
>> 
>> That's basically the route we are taking.
> 
> Ok, but for the time being anything before/after CONTEXT_KERNEL is unsafe
> except trace_hardirq_off/on() as those trace functions do not allow to
> attach anything AFAICT.

Can you point to whatever makes those particular functions special?  I failed to follow the macro maze.

> 
> Thanks,
> 
>        tglx