linux-kernel - Re: [PATCH v2] arm64: cacheflush: Fix KGDB trap detection

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Date:   Tue, 5 May 2020 16:09:16 +0100
From:   Will Deacon <will@...nel.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Douglas Anderson <dianders@...omium.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        patches@...aro.org
Subject: Re: [PATCH v2] arm64: cacheflush: Fix KGDB trap detection

On Tue, May 05, 2020 at 03:15:29PM +0100, Daniel Thompson wrote:
> On Mon, May 04, 2020 at 09:48:04PM +0100, Will Deacon wrote:
> > On Mon, May 04, 2020 at 06:05:18PM +0100, Daniel Thompson wrote:
> > > diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h
> > > index e6cca3d4acf7..ce50c1f1f1ea 100644
> > > --- a/arch/arm64/include/asm/cacheflush.h
> > > +++ b/arch/arm64/include/asm/cacheflush.h
> > > @@ -79,7 +79,7 @@ static inline void flush_icache_range(unsigned long start, unsigned long end)
> > >  	 * IPI all online CPUs so that they undergo a context synchronization
> > >  	 * event and are forced to refetch the new instructions.
> > >  	 */
> > > -#ifdef CONFIG_KGDB
> > > +
> > >  	/*
> > >  	 * KGDB performs cache maintenance with interrupts disabled, so we
> > >  	 * will deadlock trying to IPI the secondary CPUs. In theory, we can
> > > @@ -89,9 +89,9 @@ static inline void flush_icache_range(unsigned long start, unsigned long end)
> > >  	 * the patching operation, so we don't need extra IPIs here anyway.
> > >  	 * In which case, add a KGDB-specific bodge and return early.
> > >  	 */
> > > -	if (kgdb_connected && irqs_disabled())
> > > +	if (in_dbg_master())
> > 
> > Does this imply that irqs are disabled?
> 
> Yes.
> 
> Assuming CONFIG_KGDB is enabled then in_dbg_master() expands to:
> 
>     (raw_smp_processor_id() == atomic_read(&kgdb_active))

Aha, so this can drop the raw_ prefix and call smp_processor_id() instead?
I can queue the arm64 patch regardless.

Cheers,

Will