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:
> > > On Fri, Nov 20, 2020 at 12:46:23PM +0100, Juergen Gross wrote:
> > >> +static __always_inline void arch_local_irq_restore(unsigned long flags)
> > >> +{
> > >> + if (!arch_irqs_disabled_flags(flags))
> > >> + arch_local_irq_enable();
> > >> +}
> > >
> > > 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...
> > >
> > > Maybe something like:
> > >
> > > #ifdef CONFIG_DEBUG_ENTRY // for lack of something saner
> > > WARN_ON_ONCE((arch_local_save_flags() ^ flags) & X86_EFLAGS_IF);
> > > #endif
> > >
> > > At the end?
> >
> > I'd like to, but using WARN_ON_ONCE() in include/asm/irqflags.h sounds
> > like a perfect receipt for include dependency hell.
> >
> > We could use a plain asm("ud2") instead.
>
> How about out-of-lining it:
>
> #ifdef CONFIG_DEBUG_ENTRY
> extern void warn_bogus_irqrestore();
> #endif
>
> static __always_inline void arch_local_irq_restore(unsigned long flags)
> {
> if (!arch_irqs_disabled_flags(flags)) {
> arch_local_irq_enable();
> } else {
> #ifdef CONFIG_DEBUG_ENTRY
> if (unlikely(arch_local_irq_save() & X86_EFLAGS_IF))
> warn_bogus_irqrestore();
> #endif
> }
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()) \
warn_bogus_irqrestore(); \
} \
raw_local_irq_restore(flags); \
} while (0)
... perhaps? (ignoring however we deal with once-ness).
Thanks,
Mark.
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