Re: [PATCH 1/2] lockdep: improve current->(hard|soft)irqs_enabled synchronisation with actual irq state

[peterz]

On Tue, Aug 18, 2020 at 05:22:33PM +1000, Nicholas Piggin wrote:
> Excerpts from peterz@xxxxxxxxxxxxx's message of August 12, 2020 8:35 pm:
> > On Wed, Aug 12, 2020 at 06:18:28PM +1000, Nicholas Piggin wrote:
> >> Excerpts from peterz@xxxxxxxxxxxxx's message of August 7, 2020 9:11 pm:
> >> > 
> >> > What's wrong with something like this?
> >> > 
> >> > AFAICT there's no reason to actually try and add IRQ tracing here, it's
> >> > just a hand full of instructions at the most.
> >> 
> >> Because we may want to use that in other places as well, so it would
> >> be nice to have tracing.
> >> 
> >> Hmm... also, I thought NMI context was free to call local_irq_save/restore
> >> anyway so the bug would still be there in those cases?
> > 
> > NMI code has in_nmi() true, in which case the IRQ tracing is disabled
> > (except for x86 which has CONFIG_TRACE_IRQFLAGS_NMI).
> > 
> 
> That doesn't help. It doesn't fix the lockdep irq state going out of
> synch with the actual irq state. The code which triggered this with the
> special powerpc irq disable has in_nmi() true as well.

Urgh, you're talking about using lockdep_assert_irqs*() from NMI
context?

If not, I'm afraid I might've lost the plot a little on what exact
failure case we're talking about.