[PATCH 1/1 V2] Add Thread Support for the Context ID Register of ARM v6 & v7 Architectures

On Mon, Jul 25, 2011 at 11:33:23AM +0100, Russell King - ARM Linux wrote:

On Mon, Jul 25, 2011 at 12:12:29PM +0200, Wolfgang BETZ wrote:

quoted

C is a typed language for a reason.  Don't destroy it with casts.

So, the _minimum_ that needs to change in this patch is for those casts
to go, and cpu_switch_mm() needs to be fixed to take the context ID
value, rather a context ID value casted to a mm_struct.

Well, this is exactly what the patch is doing right now.
I have intentionally avoided to centralize this cast into cpu_switch_mm() in order to be sure to not miss any call to it, accidentally. As said above, the compiler will warn about something like this.
Maybe you could take a closer look at v3 of the patch, which I will send out within today.

You've completely missed my point.  What's the really scary thing here
is that you can't see that you're doing something very very wrong.

I'd still like to know why we can't avoid piggybacking on the switch_mm code
by doing similar to the hack I posted here:

http://lists.infradead.org/pipermail/linux-arm-kernel/2011-July/058436.html

Given that future cores (>= A15) put the ASID in a different register and
there's apparently a need for a thread switch notifier anyway, tying the
contextidr up so tightly with switch_mm doesn't feel right to me.

So, ugly casts aside, I'm not convinced by the approach taken here.

Will