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:

quoted

On Tue, Aug 17, 2021 at 05:40:24PM +0200, Peter Zijlstra wrote:

quoted

On Fri, Jul 30, 2021 at 12:24:34PM +0100, Will Deacon wrote:

quoted

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 <redacted>
Signed-off-by: Will Deacon <will@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 (local)

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