linux-kernel - Re: [PATCH] mm/memory_hotplug: fix wrong casting for __remove

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Message-ID: <20170913055914.3npcxevhdwghcmdd@dhcp22.suse.cz>
Date:   Wed, 13 Sep 2017 07:59:14 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     YASUAKI ISHIMATSU <yasu.isimatu@...il.com>
Cc:     linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        qiuxishi@...wei.com, arbab@...ux.vnet.ibm.com,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm/memory_hotplug: fix wrong casting for
 __remove_section()

On Tue 12-09-17 13:05:39, YASUAKI ISHIMATSU wrote:
> Hi Michal,
> 
> Thanks you for reviewing my patch.
> 
> On 09/12/2017 08:49 AM, Michal Hocko wrote:
> > On Fri 08-09-17 16:43:04, YASUAKI ISHIMATSU wrote:
> >> __remove_section() calls __remove_zone() to shrink zone and pgdat.
> >> But due to wrong castings, __remvoe_zone() cannot shrink zone
> >> and pgdat correctly if pfn is over 0xffffffff.
> >>
> >> So the patch fixes the following 3 wrong castings.
> >>
> >>   1. find_smallest_section_pfn() returns 0 or start_pfn which defined
> >>      as unsigned long. But the function always returns 32bit value
> >>      since the function is defined as int.
> >>
> >>   2. find_biggest_section_pfn() returns 0 or pfn which defined as
> >>      unsigned long. the function always returns 32bit value
> >>      since the function is defined as int.
> > 
> > this is indeed wrong. Pfns over would be really broken 15TB. Not that
> > unrealistic these days
> 
> Why 15TB?

0xffffffff>>28

-- 
Michal Hocko
SUSE Labs