linux-kernel - Re: [PATCH v4 05/10] mm: Return faster for non-fatal signals in user mode faults

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Message-ID: <20190926085849.GA3077@xz-x1>
Date:   Thu, 26 Sep 2019 16:58:49 +0800
From:   Peter Xu <peterx@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <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>,
        Marty McFadden <mcfadden8@...l.gov>, Shaohua Li <shli@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        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 v4 05/10] mm: Return faster for non-fatal signals in user
 mode faults

On Tue, Sep 24, 2019 at 08:45:18AM -0700, Matthew Wilcox wrote:

[...]

> Oh, and while you're looking at the callers of handle_mm_fault(), a
> lot of them don't check conditions in the right order.  x86, at least,
> handles FAULT_RETRY before handling FAULT_ERROR, which is clearly wrong.
> 
> Kirill and I recently discussed it here:
> https://lore.kernel.org/linux-mm/20190911152338.gqqgxrmqycodfocb@box/T/

Is there any existing path in master that we can get VM_FAULT_RETRY
returned with any existing VM_FAULT_ERROR bit?  It seems to me that
above link is the first one that is going to introduce such case?

If so, I'm uncertain now on whether I should have one patch to handle
the ERROR case first as you suggested with this series, because
otherwise that patch won't explain itself without a real benefit...

Thanks,

-- 
Peter Xu