[PATCH V2 4/6] ARM: Make PID_IN_CONTEXTIDR incompatible with PID_NS

[Will Deacon]

On Fri, Jan 24, 2014 at 05:16:28PM +0000, Adrien Vergé wrote:
> 2014/1/24 Will Deacon <will.deacon at 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.

Will