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

[Will Deacon]

On Wed, Aug 18, 2021 at 12:56:24PM +0200, Peter Zijlstra wrote:
> 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@xxxxxxx>
> > > > Signed-off-by: Will Deacon <will@xxxxxxxxxx>
> > > 
> > > 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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> 
> 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.

Agreed. The relax/force functions are already commented, so maybe alongside
SCA_USER?

Will