linux-kernel - Re: [PATCH] ARM: cache-v7: Disable preemption when reading CCSIDR

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Date:	Tue, 14 Feb 2012 12:30:00 -0500 (EST)
From:	Nicolas Pitre <nico@...xnic.net>
To:	Rabin Vincent <rabin@....in>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH] ARM: cache-v7: Disable preemption when reading CCSIDR

On Tue, 14 Feb 2012, Rabin Vincent wrote:

> On Mon, Feb 13, 2012 at 11:29:01PM +0000, Russell King - ARM Linux wrote:
> > On Mon, Feb 13, 2012 at 02:23:29PM -0800, Stephen Boyd wrote:
> > > On 02/13/12 10:15, Russell King - ARM Linux wrote:
> > > > On Mon, Feb 13, 2012 at 10:13:27AM -0800, Stephen Boyd wrote:
> > > >> Thanks. Russell has already merged the original patch to the fixes
> > > >> branch. Hopefully he can fold this one in.
> > > > Nope, I've asked Linus to pull it.
> > > >
> > > > So do we conclude that the original patch wasn't properly tested? :P
> > > 
> > > Sigh. Lockdep strikes again! I promise I tested it with lockdep disabled.
> > > 
> > > It looks like Linus' hasn't pulled yet but maybe he just hasn't
> > > published it.
> > 
> > It's not nice to change something after you've sent a pull request -
> > there's no way of knowing when Linus actually pulls it before he's
> > published it, and if he gets something different then it can raise
> > questions.
> > 
> > So, it's gone in as-is, and, as I'm now intending asking for another
> > pull request soo soon after my previous one, this is something that
> > we will have to live with probably for the remainder of the week.
> 
> OK, since it can't be folded in, here is a proper patch:
> 
> 8<---------
> >From 26f02624a20a61ed1997a4e8648e4c766a54d91d Mon Sep 17 00:00:00 2001
> From: Rabin Vincent <rabin@....in>
> Date: Tue, 14 Feb 2012 19:22:07 +0530
> Subject: [PATCH] ARM: fix v7 boot with lockdep enabled
> 
> Bootup with lockdep enabled has been broken on v7 since b46c0f74657d
> ("ARM: 7321/1: cache-v7: Disable preemption when reading CCSIDR").
> 
> This is because v7_setup (which is called very early during boot) calls
> v7_flush_dcache_all, and the save_and_disable_irqs added by that patch
> ends up attempting to call into lockdep C code (trace_hardirqs_off())
> when we are in no position to execute it (no stack, MMU off).
> 
> Fix this by using a notrace variant of save_and_disable_irqs.  The code
> already uses the notrace variant of restore_irqs.
> 
> Cc: Stephen Boyd <sboyd@...eaurora.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Nicolas Pitre <nico@...aro.org>

Reviewed-by: Nicolas Pitre <nico@...aro.org>

> Cc: stable@...r.kernel.org
> Signed-off-by: Rabin Vincent <rabin@....in>
> ---
>  arch/arm/include/asm/assembler.h |    5 +++++
>  arch/arm/mm/cache-v7.S           |    2 +-
>  2 files changed, 6 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
> index 62f8095..23371b1 100644
> --- a/arch/arm/include/asm/assembler.h
> +++ b/arch/arm/include/asm/assembler.h
> @@ -137,6 +137,11 @@
>  	disable_irq
>  	.endm
>  
> +	.macro	save_and_disable_irqs_notrace, oldcpsr
> +	mrs	\oldcpsr, cpsr
> +	disable_irq_notrace
> +	.endm
> +
>  /*
>   * Restore interrupt state previously stored in a register.  We don't
>   * guarantee that this will preserve the flags.
> diff --git a/arch/arm/mm/cache-v7.S b/arch/arm/mm/cache-v7.S
> index 7a24d396..a655d3d 100644
> --- a/arch/arm/mm/cache-v7.S
> +++ b/arch/arm/mm/cache-v7.S
> @@ -55,7 +55,7 @@ loop1:
>  	cmp	r1, #2				@ see what cache we have at this level
>  	blt	skip				@ skip if no cache, or just i-cache
>  #ifdef CONFIG_PREEMPT
> -	save_and_disable_irqs r9		@ make cssr&csidr read atomic
> +	save_and_disable_irqs_notrace r9	@ make cssr&csidr read atomic
>  #endif
>  	mcr	p15, 2, r10, c0, c0, 0		@ select current cache level in cssr
>  	isb					@ isb to sych the new cssr&csidr
> -- 
> 1.7.9
> 
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