[PATCH v11 07/16] sched: Split the guts of sched_setaffinity() into a helper function

[Peter Zijlstra]

On Wed, Aug 18, 2021 at 11:50:30AM +0100, Will Deacon wrote:
> On Tue, Aug 17, 2021 at 05:40:24PM +0200, Peter Zijlstra wrote:
> > On Fri, Jul 30, 2021 at 12:24:34PM +0100, Will Deacon wrote:
> > > In preparation for replaying user affinity requests using a saved mask,
> > > split sched_setaffinity() up so that the initial task lookup and
> > > security checks are only performed when the request is coming directly
> > > from userspace.
> > > 
> > > Reviewed-by: Valentin Schneider <Valentin.Schneider at arm.com>
> > > Signed-off-by: Will Deacon <will at kernel.org>
> > 
> > Should not sched_setaffinity() update user_cpus_ptr when it isn't NULL,
> > such that the upcoming relax_compatible_cpus_allowed_ptr() preserve the
> > full user mask?
> 
> The idea is that force_compatible_cpus_allowed_ptr() and
> relax_compatible_cpus_allowed_ptr() are used as a pair, with the former
> setting ->user_cpus_ptr and the latter restoring it. An intervening call
> to sched_setaffinity() must _clear_ the saved mask, as we discussed
> before at:
> 
> https://lore.kernel.org/r/YK53kDtczHIYumDC@hirez.programming.kicks-ass.net

Clearly that deserves a comment somewhere, because I keep trying to make
it more consistent than it can be :/ I'll see if I can find a spot.