linux-kernel - Re: [PATCH] x86/mm: Fix incorrect for loop count calculation in sync_global

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Message-ID: <20170502071837.GA2579@x1>
Date:   Tue, 2 May 2017 15:18:37 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Yinghai Lu <yinghai@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        Jinbum Park <jinb.park7@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH] x86/mm: Fix incorrect for loop count calculation in
 sync_global_pgds

On 05/01/17 at 03:37pm, Yinghai Lu wrote:
> On Mon, May 1, 2017 at 4:41 AM, Baoquan He <bhe@...hat.com> wrote:
> >  arch/x86/mm/init_64.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> > index 15173d3..dbf4f00 100644
> > --- a/arch/x86/mm/init_64.c
> > +++ b/arch/x86/mm/init_64.c
> > @@ -94,12 +94,14 @@ __setup("noexec32=", nonx32_setup);
> >   */
> >  void sync_global_pgds(unsigned long start, unsigned long end)
> >  {
> > -       unsigned long address;
> > +       unsigned long address, address_next;
> >
> > -       for (address = start; address <= end; address += PGDIR_SIZE) {
> > +       for (address = start; address <= end; address = address_next) {
> >                 const pgd_t *pgd_ref = pgd_offset_k(address);
> >                 struct page *page;
> >
> > +               address_next = (address & PGDIR_MASK) + PGDIR_SIZE;
> > +
> >                 if (pgd_none(*pgd_ref))
> >                         continue;
> >
> 
> This one is better than V2.
> 
> It would better if could rename address to addr as Ingo suggested.

Thanks for your checking and suggestion, Yinghai.

Both v1 and v2 are fine to me. As you said, code in v1 is easily
understood, while v2 code is more compact, less line. The line of v1 is
not more than 80. Maybe Ingo can help choose one which he likes better.

Thanks
Baoquan