linux-kernel - Re: [PATCH v2 05/12] x86: rework arch_local_irq

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Date:   Wed, 9 Dec 2020 15:05:39 +0100
From:   Jürgen Groß <jgross@...e.com>
To:     Mark Rutland <mark.rutland@....com>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        "VMware, Inc." <pv-drivers@...are.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Virtualization <virtualization@...ts.linux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH v2 05/12] x86: rework arch_local_irq_restore() to not use
 popf

On 09.12.20 15:02, Mark Rutland wrote:
> On Wed, Dec 09, 2020 at 01:27:10PM +0000, Mark Rutland wrote:
>> On Sun, Nov 22, 2020 at 01:44:53PM -0800, Andy Lutomirski wrote:
>>> On Sat, Nov 21, 2020 at 10:55 PM Jürgen Groß <jgross@...e.com> wrote:
>>>> On 20.11.20 12:59, Peter Zijlstra wrote:
>>>>> If someone were to write horrible code like:
>>>>>
>>>>>        local_irq_disable();
>>>>>        local_irq_save(flags);
>>>>>        local_irq_enable();
>>>>>        local_irq_restore(flags);
>>>>>
>>>>> we'd be up some creek without a paddle... now I don't _think_ we have
>>>>> genius code like that, but I'd feel saver if we can haz an assertion in
>>>>> there somewhere...
> 
>> I was just talking to Peter on IRC about implementing the same thing for
>> arm64, so could we put this in the generic irqflags code? IIUC we can
>> use raw_irqs_disabled() to do the check.
>>
>> As this isn't really entry specific (and IIUC the cases this should
>> catch would break lockdep today), maybe we should add a new
>> DEBUG_IRQFLAGS for this, that DEBUG_LOCKDEP can also select?
>>
>> Something like:
>>
>> #define local_irq_restore(flags)                               \
>>         do {                                                    \
>>                 if (!raw_irqs_disabled_flags(flags)) {          \
>>                         trace_hardirqs_on();                    \
>>                 } else if (IS_ENABLED(CONFIG_DEBUG_IRQFLAGS) {  \
>>                         if (unlikely(raw_irqs_disabled())       \
> 
> Whoops; that should be !raw_irqs_disabled().
> 
>>                                 warn_bogus_irqrestore();        \
>>                 }                                               \
>>                 raw_local_irq_restore(flags);                   \
>>          } while (0)
>>
>> ... perhaps? (ignoring however we deal with once-ness).
> 
> If no-one shouts in the next day or two I'll spin this as its own patch.

Fine with me. So I'll just ignore a potential error case in my patch.

Thanks,


Juergen


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