linux-kernel - Re: [PATCH v5 3/3] userfaultfd: use per-vma locks in userfaultfd operations

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Message-ID: <CA+EESO6TowKNh10+tzwawBemykVcVDP+_ep1fg-_RiqBzfR7ew@mail.gmail.com>
Date: Tue, 13 Feb 2024 11:36:52 -0800
From: Lokesh Gidra <lokeshgidra@...gle.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>, akpm@...ux-foundation.org, 
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, selinux@...r.kernel.org, 
	kernel-team@...roid.com, aarcange@...hat.com, peterx@...hat.com, 
	david@...hat.com, axelrasmussen@...gle.com, bgeffon@...gle.com, 
	willy@...radead.org, jannh@...gle.com, kaleshsingh@...gle.com, 
	ngeoffray@...gle.com, timmurray@...gle.com, rppt@...nel.org
Subject: Re: [PATCH v5 3/3] userfaultfd: use per-vma locks in userfaultfd operations

On Tue, Feb 13, 2024 at 11:31 AM Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> On Tue, Feb 13, 2024 at 11:27 AM Liam R. Howlett
> <Liam.Howlett@...cle.com> wrote:
> >
> > * Lokesh Gidra <lokeshgidra@...gle.com> [240213 14:18]:
> > ...
> >
> > > > > We could use something like uffd_prepare(), uffd_complete() but I
> > > > > thought of those names rather late in the cycle, but I've already caused
> > > > > many iterations of this patch set and that clean up didn't seem as vital
> > > > > as simplicity and clarity of the locking code.
> > >
> > > I anyway have to send another version to fix the error handling that
> > > you reported earlier. I can take care of this in that version.
> > >
> > > mfill_atomic...() functions (annoyingly) have to sometimes unlock and
> > > relock. Using prepare/complete in that context seems incompatible.
> > >
> > > >
> > > > Maybe lock_vma_for_uffd()/unlock_vma_for_uffd()? Whatever name is
> > > > better I'm fine with it but all these #ifdef's sprinkled around don't
> > > > contribute to the readability.
> > >
> > > I'll wait for an agreement on this because I too don't like using so
> > > many ifdef's either.
> > >
> > > Since these functions are supposed to have prototype depending on
> > > mfill/move, how about the following names:
> > >
> > > uffd_lock_mfill_vma()/uffd_unlock_mfill_vma()
> > > uffd_lock_move_vmas()/uffd_unlock_move_vmas()
> > >
> > > Of course, I'm open to other suggestions as well.
> > >
> >
> > I'm happy with those if you remove the vma/vmas from the name.
>
> Sounds good to me.
>
Sure. I'll do that:

Asking to avoid any more iterations: these functions should call the
currently defined ones or should replace them. For instance, should I
do the following:

#ifdef CONFIG_PER_VMA_LOCK
.. uffd_mfill_lock()
{
        return find_and_lock_dst_vma(...);
}
#else
..uffd_mfill_lock()
{
       return lock_mm_and_find_dst_vma(...);
}
#endif

or have the function replace
find_and_lock_dst_vma()/lock_mm_and_find_dst_vma() ?

> >
> > --
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> >