From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Fri, 24 Jan 2014 17:17:55 +0000 Subject: [PATCH V2 4/6] ARM: Make PID_IN_CONTEXTIDR incompatible with PID_NS In-Reply-To: References: <1390581656-16372-1-git-send-email-adrienverge@gmail.com> <1390581656-16372-5-git-send-email-adrienverge@gmail.com> <20140124164343.GJ31040@mudshark.cambridge.arm.com> Message-ID: <20140124171754.GM31040@mudshark.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Jan 24, 2014 at 05:16:28PM +0000, Adrien Verg? wrote: > 2014/1/24 Will Deacon : > > 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? I think I'd rather have the global ID than disable a potentially useful feature, especially since this is likely to be consumed by external trace tools as opposed to user-space tasks. Will