Messages in this thread | | | Date | Fri, 24 Jan 2014 14:12:09 -0500 | From | Christopher Covington <> | Subject | Re: [PATCH V2 4/6] ARM: Make PID_IN_CONTEXTIDR incompatible with PID_NS |
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On 01/24/2014 12:52 PM, Christopher Covington wrote: > On 01/24/2014 12:17 PM, Will Deacon wrote: >> On Fri, Jan 24, 2014 at 05:16:28PM +0000, Adrien Vergé wrote: >>> 2014/1/24 Will Deacon <will.deacon@arm.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? >> >> 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. > > We've discussed before that the ARM architecture doesn't say what should be > written to the CONTEXTIDR, so it's up to us to decide. Will has a use case > where the global PID is useful. Adrien's patches present a use case where I > think the virtual PID would be useful. I've done work in the past where > writing the process group ID was useful. Would it be reasonable to make what's > written to the CONTEXTIDR run-time configurable? If so, what would be the best > interface for configuring it?
D'oh, I mixed things up. For ETM to work it can only use global PID's in the CONTEXTIDR.
Christopher
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