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

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Message-ID: <20161129032212.GA1727@aaronlu.sh.intel.com>
Date:   Tue, 29 Nov 2016 11:22:12 +0800
From:   Aaron Lu <aaron.lu@...el.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
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 07:06:39PM -0800, Linus Torvalds wrote:
> 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.

Right, I just did a build test.
Now I'm doing more tests, sorry for being careless.

Regards,
Aaron

> 
> > +               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
> 
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