linux-kernel - Re: [PATCH v4 7/8] lockdep: Change hardirq{s_enabled,

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Message-ID: <20200623163730.GA4800@hirez.programming.kicks-ass.net>
Date:   Tue, 23 Jun 2020 18:37:30 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Ahmed S. Darwish" <a.darwish@...utronix.de>
Cc:     mingo@...nel.org, will@...nel.org, tglx@...utronix.de,
        x86@...nel.org, linux-kernel@...r.kernel.org, rostedt@...dmis.org,
        bigeasy@...utronix.de, davem@...emloft.net,
        sparclinux@...r.kernel.org, mpe@...erman.id.au,
        linuxppc-dev@...ts.ozlabs.org, heiko.carstens@...ibm.com,
        linux-s390@...r.kernel.org, linux@...linux.org.uk, elver@...gle.com
Subject: Re: [PATCH v4 7/8] lockdep: Change hardirq{s_enabled,_context} to
 per-cpu variables

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().