linux-kernel - Re: [PATCH v2] mm/hugetlb: fix a addressing exception caused by huge_pte

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Message-Id: <D70C23C6-75CB-4A68-8E7C-23FE8A0CCA68@lca.pw>
Date:   Sat, 22 Feb 2020 06:50:42 -0500
From:   Qian Cai <cai@....pw>
To:     "Longpeng (Mike)" <longpeng2@...wei.com>
Cc:     akpm@...ux-foundation.org, mike.kravetz@...cle.com,
        kirill.shutemov@...ux.intel.com, linux-kernel@...r.kernel.org,
        arei.gonglei@...wei.com, weidong.huang@...wei.com,
        weifuqiang@...wei.com, kvm@...r.kernel.org, linux-mm@...ck.org,
        Matthew Wilcox <willy@...radead.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] mm/hugetlb: fix a addressing exception caused by huge_pte_offset()



> On Feb 22, 2020, at 1:33 AM, Longpeng (Mike) <longpeng2@...wei.com> wrote:
> 
> As explained in the commit messages, it's for safe(e.g. avoid the compilier
> mischief). You can also find the same usage in the ARM64's huge_pte_offset() in
> arch/arm64/mm/hugetlbpage.c

Rather than blindly copy over there, are those correct here? What kind of bad compiler optimizations exactly do they try to prevent? Until we understand those details, blindly adding READ_ONCE() will only hide other problems.