Re: [PATCH v5 9/9] binder: use per-vma lock in page reclaiming

Suren Baghdasaryan
2024-11-26T20:06:11Z

On Tue, Nov 26, 2024 at 11:11 AM Carlos Llamas <cmllamas@google.com> wrote:
>
> On Tue, Nov 26, 2024 at 10:46:03AM -0800, Suren Baghdasaryan wrote:
> > On Tue, Nov 26, 2024 at 10:45 AM Suren Baghdasaryan <surenb@google.com> wrote:
> > >
> > > You did add a clarifying comment I asked for in
> > > https://lore.kernel.org/all/CAJuCfpESdY4L_sSwiCYVCX+5y1WOuAjLNPw35pEGzTSyoHFYPA@mail.gmail.com/
> >
> > s/did/did not
>
> Oh, I added the comment to patch 5/9 since it fits better there (sorry
> that I forgot to mention this). Now the kerneldoc section reads:
>
> + * @mapped: whether the vm area is mapped, each binder instance is
> + * allowed a single mapping throughout its lifetime
>
> ... and the vma check now has the following comment:
>
> + /* ensure the vma corresponds to the binder mapping */

I think the above comment does not explain the race we are trying to avoid here.
Something like this perhaps:
/*
* binder does not allow mapping of the same buffer more than once, therefore
* alloc->vm_start could not have changed since the buffer can't be remapped.
* Checking binder_alloc_is_mapped() ensures that the vma is mapped and still
* covers the same area.
*/

> + if (vma && !binder_alloc_is_mapped(alloc))
> goto err_invalid_vma;
>
> This was the feedback right?