linux-kernel - Re: [PATCH] mremap: move_ptes: check pte dirty after its removal

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Date:   Mon, 28 Nov 2016 19:06:39 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Aaron Lu <aaron.lu@...el.com>
Cc:     Linux Memory Management List <linux-mm@...ck.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Huang Ying <ying.huang@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mremap: move_ptes: check pte dirty after its removal

On Mon, Nov 28, 2016 at 6:57 PM, Aaron Lu <aaron.lu@...el.com> wrote:
>
> Here is a fix patch, sorry for the trouble.

I don't think you tested this one.. You've now essentially reverted
5d1904204c99 entirely by making the new force_flush logic a no-op.

> +               pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
>                 if (pmd_present(*old_pmd) && pmd_dirty(*old_pmd))
>                         force_flush = true;

You need to be testing "pmd", not "*old_pmd".

Because now "*old_pmd" will be zeroes.

>                 if (pte_present(*old_pte) && pte_dirty(*old_pte))
>                         force_flush = true;

Similarly here. You need to check "pte", not "*old_pte".

            Linus