Re: [PATCH v2 03/36] mm: use do_futex() instead of sys_futex() in mm_release()

[Darren Hart]

On Fri, Mar 16, 2018 at 07:03:53PM +0000, Andy Lutomirski wrote:
> On Fri, Mar 16, 2018 at 6:43 PM, Darren Hart <dvhart@xxxxxxxxxxxxx> wrote:
> > On Thu, Mar 15, 2018 at 08:04:56PM +0100, Dominik Brodowski wrote:
> >> sys_futex() is a wrapper to do_futex() which does not modify any
> >> values here:
> >>
> >> - uaddr, val and val3 are kept the same
> >>
> >> - op is masked with FUTEX_CMD_MASK, but is always set to FUTEX_WAKE.
> >>   Therefore, val2 is always 0.
> >>
> >> - as utime is set to NULL, *timeout is NULL
> >>
> >> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> >> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> >> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> >> Cc: Darren Hart <dvhart@xxxxxxxxxxxxx>
> >> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> >> Signed-off-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
> >
> > Hi Dominik,
> >
> > I'm missing the "why" part here. What is it you are trying to address?
> >
> > do_futex is not currently in use outside of the futex implementation,
> > while sys_futex is. This decouples the interface from the
> > implementation. While this is perhaps less critical within the
> > kernel, I don't see a compelling reason to increase the coupling
> > between the mm and futex implementations.
> >
> > Without a compelling WHY, Nack from me.
> >
> 
> We want to make some changes to the way that the syscall entry code
> invokes syscalls, and these changes will make it impossible to call
> sys_xyz() functions from the kernel.  So we can make sys_futex() be a
> trivial wrapper around a new ksys_futex(), or we can do a patch like
> this.

I dug up the cover letter and got the motivation and withdraw my
objection. I understand the motivation to put the motivation in the
cover letter in a large series, but I think there should have been
something indicating the need for this change in the individual patches,
even just a single line like Andy's first sentence above.

Thanks,

-- 
Darren Hart
VMware Open Source Technology Center