Re: [RFC 09/10] x86/mm: Rework lazy TLB to track the actual loaded mm

Ingo Molnar
2017-05-10T08:24:46Z

* Thomas Gleixner <tglx@linutronix.de> wrote:

> On Wed, 10 May 2017, Ingo Molnar wrote:
> >
> > * Thomas Gleixner <tglx@linutronix.de> wrote:
> >
> > > On Sun, 7 May 2017, Andy Lutomirski wrote:
> > > > /* context.lock is held for us, so we don't need any locking. */
> > > > static void flush_ldt(void *current_mm)
> > > > {
> > > > + struct mm_struct *mm = current_mm;
> > > > mm_context_t *pc;
> > > >
> > > > - if (current->active_mm != current_mm)
> > > > + if (this_cpu_read(cpu_tlbstate.loaded_mm) != current_mm)
> > >
> > > While functional correct, this really should compare against 'mm'.
> > >
> > > > return;
> > > >
> > > > - pc = &current->active_mm->context;
> > > > + pc = &mm->context;
> >
> > So this appears to be the function:
> >
> > static void flush_ldt(void *current_mm)
> > {
> > struct mm_struct *mm = current_mm;
> > mm_context_t *pc;
> >
> > if (this_cpu_read(cpu_tlbstate.loaded_mm) != current_mm)
> > return;
> >
> > pc = &mm->context;
> > set_ldt(pc->ldt->entries, pc->ldt->size);
> > }
> >
> > why not rename 'current_mm' to 'mm' and remove the 'mm' local variable?
>
> Because you cannot dereference a void pointer, i.e. &mm->context ....

Indeed, doh! The naming totally confused me. The way I'd write it is the canonical
form for such callbacks:

static void flush_ldt(void *data)
{
struct mm_struct *mm = data;

... which beyond unconfusing me would probably also have prevented any accidental
use of the 'current_mm' callback argument.

Thanks,

Ingo