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

[Will Deacon]

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

Will