linux-kernel - Re: [PATCH V2 4/6] ARM: Make PID_IN_CONTEXTIDR incompatible with PID

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Message-ID: <20140124164343.GJ31040@mudshark.cambridge.arm.com>
Date:	Fri, 24 Jan 2014 16:43:43 +0000
From:	Will Deacon <will.deacon@....com>
To:	Adrien Vergé <adrienverge@...il.com>
Cc:	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Mathieu Poirier <mathieu.poirier@...aro.org>,
	Christopher Covington <cov@...eaurora.org>,
	Dirk Behme <dirk.behme@...bosch.com>,
	Michel Dagenais <michel.dagenais@...ymtl.ca>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 4/6] ARM: Make PID_IN_CONTEXTIDR incompatible with
 PID_NS

On Fri, Jan 24, 2014 at 04:40:54PM +0000, Adrien Vergé wrote:
> When using namespaces, different processes can have the same PID.
> It makes no sense to store a PID value in the Context ID register
> to track a specific process, when others share the same value.
> 
> Consequently, PID_IN_CONTEXTIDR (which is used for tracing and
> debugging processes) should not be compatible with PID_NS.
> 
> Signed-off-by: Adrien Vergé <adrienverge@...il.com>
> ---
>  arch/arm/Kconfig.debug   | 2 +-
>  arch/arm64/Kconfig.debug | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
> index 5765abf..ed46748 100644
> --- a/arch/arm/Kconfig.debug
> +++ b/arch/arm/Kconfig.debug
> @@ -1143,7 +1143,7 @@ config ARM_KPROBES_TEST
>  
>  config PID_IN_CONTEXTIDR
>  	bool "Write the current PID to the CONTEXTIDR register"
> -	depends on CPU_COPY_V6
> +	depends on CPU_COPY_V6 && !PID_NS
>  	help
>  	  Enabling this option causes the kernel to write the current PID to
>  	  the PROCID field of the CONTEXTIDR register, at the expense of some
> diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
> index 835c559..06b2633b 100644
> --- a/arch/arm64/Kconfig.debug
> +++ b/arch/arm64/Kconfig.debug
> @@ -17,6 +17,7 @@ config EARLY_PRINTK
>  
>  config PID_IN_CONTEXTIDR
>  	bool "Write the current PID to the CONTEXTIDR register"
> +	depends on !PID_NS
>  	help
>  	  Enabling this option causes the kernel to write the current PID to
>  	  the CONTEXTIDR register, at the expense of some additional

Are you sure about this? The value we write is actually task_pid_nr, which I
believe to be globally unique.

Will
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