DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 640C6437F7C
Reply-To: xlpang@redhat.com
Subject: Re: [PATCH v3 1/3] kexec: Move vmcoreinfo out of the kernel's .bss
 section
References: <1489989033-1179-1-git-send-email-xlpang@redhat.com>
 <87pohbz4lo.fsf@xmission.com>
 <20170322025536.GA4424@dhcp-128-65.nay.redhat.com>
 <87pohaxam1.fsf@xmission.com>
 <20170322043004.GB4424@dhcp-128-65.nay.redhat.com>
 <20170322214819.0b64d49c@TP-holzheu>
To: Michael Holzheu <holzheu@linux.vnet.ibm.com>,
        Dave Young <dyoung@redhat.com>
Cc: Baoquan He <bhe@redhat.com>, Xunlei Pang <xlpang@redhat.com>,
        Atsushi Kumagai <ats-kumagai@wm.jp.nec.com>,
        Petr Tesarik <ptesarik@suse.cz>, linux-kernel@vger.kernel.org,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        hbathini@linux.vnet.ibm.com, akpm@linux-foundation.org,
        kexec@lists.infradead.org
From: Xunlei Pang <xpang@redhat.com>
Message-ID: <58D39429.9020200@redhat.com>
Date: Thu, 23 Mar 2017 17:23:53 +0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.2.0
MIME-Version: 1.0
In-Reply-To: <20170322214819.0b64d49c@TP-holzheu>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2544
Lines: 71

On 03/23/2017 at 04:48 AM, Michael Holzheu wrote:
> Am Wed, 22 Mar 2017 12:30:04 +0800
> schrieb Dave Young <dyoung@redhat.com>:
>
>> On 03/21/17 at 10:18pm, Eric W. Biederman wrote:
>>> Dave Young <dyoung@redhat.com> writes:
>>>
> [snip]
>
>>>> I think makedumpfile is using it, but I also vote to remove the
>>>> CRASHTIME. It is better not to do this while crashing and a makedumpfile
>>>> userspace patch is needed to drop the use of it.
>>>>
>>>>> As we are looking at reliability concerns removing CRASHTIME should make
>>>>> everything in vmcoreinfo a boot time constant.  Which should simplify
>>>>> everything considerably.
>>>> It is a nice improvement..
>>> We also need to take a close look at what s390 is doing with vmcoreinfo.
>>> As apparently it is reading it in a different kind of crashdump process.
>> Yes, need careful review from s390 and maybe ppc64 especially about
>> patch 2/3, better to have comments from IBM about s390 dump tool and ppc
>> fadump. Added more cc.
> On s390 we have at least an issue with patch 1/3. For stand-alone dump
> and also because we create the ELF header for kdump in the new
> kernel we save the pointer to the vmcoreinfo note in the old kernel on a
> defined memory address in our absolute zero lowcore.
>
> This is done in arch/s390/kernel/setup.c:
>
> static void __init setup_vmcoreinfo(void)
> {
>         mem_assign_absolute(S390_lowcore.vmcore_info, paddr_vmcoreinfo_note());
> }
>
> Since with patch 1/3 paddr_vmcoreinfo_note() returns NULL at this point in
> time we have a problem here.
>
> To solve this - I think - we could move the initialization to
> arch/s390/kernel/machine_kexec.c:
>
> void arch_crash_save_vmcoreinfo(void)
> {
>         VMCOREINFO_SYMBOL(lowcore_ptr);
>         VMCOREINFO_SYMBOL(high_memory);
>         VMCOREINFO_LENGTH(lowcore_ptr, NR_CPUS);
>         mem_assign_absolute(S390_lowcore.vmcore_info, paddr_vmcoreinfo_note());
> }
>
> Probably related to this is my observation that patch 3/3 leads to
> an empty VMCOREINFO note for kdump on s390. The note is there ...
>
> # readelf -n /var/crash/127.0.0.1-2017-03-22-21:14:39/vmcore | grep VMCORE
>   VMCOREINFO           0x0000068e       Unknown note type: (0x00000000)
>
> But it contains only zeros.

Yes, this is a good catch, I will do more tests.

Thanks,
Xunlei

>
> Unfortunately I have not yet understood the reason for this.
>
> Michael
>
>
> _______________________________________________
> kexec mailing list
> kexec@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec