linux-kernel - Re: [PATCH v5 02/25] mm: userfault: return VM_FAULT

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Message-ID: <CAHk-=whRw_6ZTj=AT=cRoSTyoEk2-hiqJoNkqgWE-gSRVE5YwQ@mail.gmail.com>
Date:   Mon, 24 Jun 2019 21:31:42 +0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Xu <peterx@...hat.com>
Cc:     Linux-MM <linux-mm@...ck.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Maya Gokhale <gokhale2@...l.gov>,
        Jerome Glisse <jglisse@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Martin Cracauer <cracauer@...s.org>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        Shaohua Li <shli@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Marty McFadden <mcfadden8@...l.gov>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>
Subject: Re: [PATCH v5 02/25] mm: userfault: return VM_FAULT_RETRY on signals

On Mon, Jun 24, 2019 at 3:43 PM Peter Xu <peterx@...hat.com> wrote:
>
> Should we still be able to react on signal_pending() as part of fault
> handling (because that's what this patch wants to do, at least for an
> user-mode page fault)?  Please kindly correct me if I misunderstood...

I think that with this patch (modulo possible fix-ups) then yes, as
long as we're returning to user mode we can do signal_pending() and
return RETRY.

But I think we really want to add a new FAULT_FLAG_INTERRUPTIBLE bit
for that (the same way we already have FAULT_FLAG_KILLABLE for things
that can react to fatal signals), and only do it when that is set.
Then the page fault handler can set that flag when it's doing a
user-mode page fault.

Does that sound reasonable?

               Linus