linux-kernel - Re: [RFC 1/8] mm: add overflow and underflow checks for page->

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Message-ID: <CAMZfGtVS2ZRAsd9HLODoLa1vVp0XCcBOTXjsmpoWwDcdGaADvQ@mail.gmail.com>
Date:   Wed, 27 Oct 2021 15:46:42 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Pasha Tatashin <pasha.tatashin@...een.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-m68k@...ts.linux-m68k.org,
        Anshuman Khandual <anshuman.khandual@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        william.kucharski@...cle.com,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, geert@...ux-m68k.org,
        schmitzmic@...il.com, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>, weixugc@...gle.com,
        Greg Thelen <gthelen@...gle.com>
Subject: Re: [RFC 1/8] mm: add overflow and underflow checks for page->_refcount

On Wed, Oct 27, 2021 at 1:38 AM Pasha Tatashin
<pasha.tatashin@...een.com> wrote:
>
> The problems with page->_refcount are hard to debug, because usually
> when they are detected, the damage has occurred a long time ago. Yet,
> the problems with invalid page refcount may be catastrophic and lead to
> memory corruptions.
>
> Reduce the scope of when the _refcount problems manifest themselves by
> adding checks for underflows and overflows into functions that modify
> _refcount.
>
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>

I found some atomic_add/dec are replaced with atomic_add/dec_return,
those helpers with return value imply a full memory barrier around it, but
others without return value do not. Do you have any numbers to show
the impact? Maybe atomic_add/dec_return_relaxed can help this.

Thanks.