Re: [PATCH v2 4/6] mm: lock vma explicitly before doing vm_flags_reset and vm_flags_reset_once

[Linus Torvalds <torvalds@linux-foundation.org>]

On Tue, 1 Aug 2023 at 15:07, Suren Baghdasaryan <surenb@google.com> wrote:
>
>       To make locking more visible, change these
> functions to assert that the vma write lock is taken and explicitly lock
> the vma beforehand.

So I obviously think this is a good change, but the fact that it
touched driver files makes me go "we're still doing something wrong".

I'm not super-happy with hfi1_file_mmap() doing something like
vma_start_write(), in that I *really* don't think drivers should ever
have to think about issues like this.

And I think it's unnecessary.  This is the mmap op in the
hfi1_file_ops, and I think that any actual mmap() code had _better_
had locked the new vma before asking any driver to set things up (and
the assert would catch it if somebody didn't).

I realize that it doesn't hurt in a technical sense, but I think
having drivers call these VM-internal subtle locking functions does
hurt in a maintenance sense, so we should make sure to not have it.

                   Linus