Re: [PATCH v2 05/12] x86: rework arch_local_irq_restore() to not use popf

[Jürgen Groß <jgross@xxxxxxxx>]

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@xxxxxxxx> 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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