[PATCH v4 7/8] lockdep: Change hardirq{s_enabled,_context} to per-cpu variables

[Peter Zijlstra]

On Tue, Jun 23, 2020 at 06:13:21PM +0200, Ahmed S. Darwish wrote:
> Well, freshly merged code is using it. For example, KCSAN:
> 
>     => f1bc96210c6a ("kcsan: Make KCSAN compatible with lockdep")
>     => kernel/kcsan/report.c:
> 
>     void kcsan_report(...)
>     {
> 	...
>         /*
>          * With TRACE_IRQFLAGS, lockdep's IRQ trace state becomes corrupted if
>          * we do not turn off lockdep here; this could happen due to recursion
>          * into lockdep via KCSAN if we detect a race in utilities used by
>          * lockdep.
>          */
>         lockdep_off();
> 	...
>     }

Marco, do you remember what exactly happened there? Because I'm about to
wreck that. That is, I'm going to make TRACE_IRQFLAGS ignore
lockdep_off().