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

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Date:	Fri, 24 Jan 2014 12:16:28 -0500
From:	Adrien Vergé <adrienverge@...il.com>
To:	Will Deacon <will.deacon@....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

2014/1/24 Will Deacon <will.deacon@....com>:
> Are you sure about this? The value we write is actually task_pid_nr, which I
> believe to be globally unique.

You are right: the task_pid_nr is unique in the system. However when
using namespaces, the so called "PID" is the virtual number that
processes in different namespaces can share.

This PID is the one visible by user-space tasks, in particular
user-space tracers and debuggers. These programs would expect to find
the PID of the traced process in the Context ID reg, while it is not.
I think it is better to remove confusion by making PID_IN_CONTEXTIDR
and PID_NS incompatible.

What do you think?
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