linux-kernel - Re: [PATCH v4 1/4] mm: Don't skip swap entry even if zap

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Message-ID: <Yg3NdtG4Y63OCYxe@xz-m1.local>
Date:   Thu, 17 Feb 2022 12:22:14 +0800
From:   Peter Xu <peterx@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Matthew Wilcox <willy@...radead.org>,
        Yang Shi <shy828301@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Alistair Popple <apopple@...dia.com>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v4 1/4] mm: Don't skip swap entry even if zap_details
 specified

On Wed, Feb 16, 2022 at 06:54:55PM -0800, Andrew Morton wrote:
> On Wed, 16 Feb 2022 17:48:07 +0800 Peter Xu <peterx@...hat.com> wrote:
> 
> > The "details" pointer shouldn't be the token to decide whether we should skip
> > swap entries.  For example, when the user specified details->zap_mapping==NULL,
> > it means the user wants to zap all the pages (including COWed pages), then we
> > need to look into swap entries because there can be private COWed pages that
> > was swapped out.
> 
> I assume "user" here means "caller".

Right.

> 
> > Skipping some swap entries when details is non-NULL may lead to wrongly leaving
> > some of the swap entries while we should have zapped them.
> > 
> > A reproducer of the problem:
> > 
> > ...
> >
> > The issue seems to exist starting from the initial commit of git.
> 
> I'll add cc:stable to this one, thanks.

Yes, thanks.

I didn't yet check the backports to stable yet, some of them might need some
tweaks on the patch.  I'll follow that up when it hits it.

-- 
Peter Xu