linux-kernel - Re: [PATCH v5 6/6] mm: handle userfaults under VMA lock

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Date:   Wed, 28 Jun 2023 17:19:31 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     akpm@...ux-foundation.org, willy@...radead.org, hannes@...xchg.org,
        mhocko@...e.com, josef@...icpanda.com, jack@...e.cz,
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        viro@...iv.linux.org.uk, brauner@...nel.org,
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        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH v5 6/6] mm: handle userfaults under VMA lock

On Wed, Jun 28, 2023 at 10:32 AM Peter Xu <peterx@...hat.com> wrote:
>
> On Wed, Jun 28, 2023 at 10:25:29AM -0700, Suren Baghdasaryan wrote:
> > Enable handle_userfault to operate under VMA lock by releasing VMA lock
> > instead of mmap_lock and retrying. Note that FAULT_FLAG_RETRY_NOWAIT
> > should never be used when handling faults under per-VMA lock protection
> > because that would break the assumption that lock is dropped on retry.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
>
> Maybe the sanitize_fault_flags() changes suite more in patch 3, but not a
> big deal I guess.

IIUC FAULT_FLAG_RETRY_NOWAIT comes into play in this patchset only in
the context of uffds, therefore that check seems to be needed when we
enable per-VMA lock uffd support, which is this patch. Does that make
sense?

>
> Acked-by: Peter Xu <peterx@...hat.com>

Thanks!

>
> Thanks!
>
> --
> Peter Xu
>