Re: [PATCH net-next] net: add in_softirq() debug checking in napi_consume_skb()

[Jakub Kicinski]

On Wed, 18 Nov 2020 16:57:57 +0100 Peter Zijlstra wrote:
> On Wed, Nov 18, 2020 at 07:43:48AM -0800, Jakub Kicinski wrote:
> 
> > TBH the last sentence I wrote isn't clear even to me at this point ;D
> > 
> > Maybe using just the macros from preempt.h - like this?
> > 
> > #define lockdep_assert_in_softirq()                                    \
> > do {                                                                   \
> >        WARN_ON_ONCE(__lockdep_enabled                  &&              \
> >                     (!in_softirq() || in_irq() || in_nmi())	\
> > } while (0)
> > 
> > We know what we're doing so in_softirq() should be fine (famous last
> > words).  
> 
> So that's not actually using any lockdep state. But if that's what you
> need, I don't have any real complaints.

Great, thanks! 

The motivation was to piggy back on lockdep rather than adding a
one-off Kconfig knob for a check in the fast path in networking.