From: Alexander Egorenkov <egorenar@linux.ibm.com>
To: "HAGIO KAZUHITO(萩尾 一仁)" <k-hagio-ab@nec.com>
Cc: "kexec@lists.infradead.org" <kexec@lists.infradead.org>,
"Discussion list for crash utility usage,
maintenance and development" <crash-utility@redhat.com>
Subject: RE: [PATCH 1/1] fix left bit-shift overflow in __exclude_unnecessary_pages()
Date: Wed, 01 Sep 2021 11:27:49 +0200 [thread overview]
Message-ID: <87v93ksl0q.fsf@oc8242746057.ibm.com> (raw)
In-Reply-To: <TYYPR01MB67777DFB702E9801AA414B6ADDCD9@TYYPR01MB6777.jpnprd01.prod.outlook.com>
In-Reply-To:
Hi Kazu,
HAGIO KAZUHITO(萩尾 一仁) <k-hagio-ab@nec.com> writes:
> Hi Alex,
> +cc kexec list (the right one for makedumpfile patch)
>
Thanks, sorry for the mix up :(
> -----Original Message-----
>> Whenever the variables compound_order or private become greater than
>> 31, left bit-shift of 1 overflows, and nr_pages becomes zero. If nr_pages
>> becomes 0 and pages are being excluded at the end of the PFN loop, the
>> else branch of the last if statement is entered and pfn is decremented by
>> 1 because nr_pages is 0. Finally, this causes the loop variable pfn to
>> be assigned the same value as before when the next loop iteration begins
>> which results in an infinite loop.
>>
>> This issue appeared on s390 64bit architecture with a dump of 16GB RAM.
>
> The patch looks good to me, but just out of curiosity, when do the
> compound_order or private become greater than 31 on s390?
>
> Thanks,
> Kazu
>
I added some debug statements and this what i got:
compound_order 0
compound_order 1
compound_order 2
compound_order 3
compound_order 4
compound_order 5
compound_order 6
compound_order 7
compound_order 8
private 0
private 1
private 2
private 3
private 4
private 5
private 52
private 6
private 7
private 8
It seems that not compound_order but private is at fault here and
triggers the bug. Not sure yet what that exactly means and whether we
have here another bug which triggers this one :/
Regards
Alex
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next prev parent reply other threads:[~2021-09-01 9:28 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-01 9:10 [PATCH 1/1] fix left bit-shift overflow in __exclude_unnecessary_pages() HAGIO KAZUHITO(萩尾 一仁)
2021-09-01 9:27 ` Alexander Egorenkov [this message]
2021-09-02 2:04 ` HAGIO KAZUHITO(萩尾 一仁)
2021-09-02 6:11 ` Alexander Egorenkov
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