On 02/06/2020 11:46 AM, piliu wrote:
>
>
> On 02/05/2020 05:18 AM, HAGIO KAZUHITO(萩尾 一仁) wrote:
>>> -----Original Message-----
>>> On Tue, Feb 04, 2020 at 02:24:17PM +0800, piliu wrote:
>>>> Hi,
>>>>
>>>> Sorry to reply late due to a long festival.
>>>>
>>>> I have tested this patch against v4.15 and latest kernel with small
>>>> modification to meet the situation we discussed here. Both work fine.
>>>>
>>>> The below is the modification of two kernel
>>>>
>>>> test1. latest kernel with two extra modification to expose the problem
>>>> -1.1 reverts commit 1f503443e7df8dc8366608b4d810ce2d6669827c
>>>> (mm/sparse.c: reset section's mem_map when fully deactivated), this
>>>> commit work around this bug
>>>> -1.2. reverts commit a0b1280368d1e91ab72f849ef095b4f07a39bbf1 ("kdump:
>>>> write correct address of mem_section into vmcoreinfo"). This will create
>>>> a buggy situation as we discussed here.
>>>> -1.3. fix building bug due to revert
>>>> a0b1280368d1e91ab72f849ef095b4f07a39bbf1
>>>>
>>>> test2. v4.15, which include both commit 83e3c48729d9 and a0b1280368d1.
>>>> -2.1. revert commit a0b1280368d1e91ab72f849ef095b4f07a39bbf1 ("kdump:
>>>> write correct address of mem_section into vmcoreinfo")
>>>>
>>>> So I can not see any problem with my patch.
>>>> Maybe I misunderstand the discussion, but I can not see my original
>>>> patch will break the kernel which have 83e3c48729d9 but not a0b1280368d1.
>>>>
>>>> Thanks,
>>>> Pingfan
>>>>
>>>
>>> You also need to test the case where 83e3c48729d9 is not present at all. Can
>>> you test on a 4.4 kernel, for example? As far as I understand, a vanilla 4.4
>>> kernel would not be dumpable with your patch.
>>
>> As far as I've tested this patch with SPARSEMEM_EXTREME vmcores below, it's
>> OK:
>> - 51 vmcores of vanilla kernels (each from 2.6.36 through 5.5) on hand
>> - one more vanilla 4.4.0 kernel with a different config from the above
>>
>> So apparently not all vanilla 4.4 kernels are affected by the patch.
>>
> Sorry, due to touch hardware resource in our lab, I can not have a test
> on v4.4 on a system with hotplug memory yet. I still try to find some
> resource.
>
> But from the logic of this patch, it just does the following changes:
> -1. After memory hot-removed, either mem_section.section_mem_map = NULL
> or mem_section.section_mem_map without SECTION_MARKED_PRESENT, we will
> have mem_maps[section_nr] = mem_map = NOT_MEMMAP_ADDR, so later it will
> be skipped.
> -2. If not populated, mem_section.section_mem_map = NULL. It can follow
> the same handling of hot-removed, and be skipped during parsing.
>
> And in v4.4 sparse_remove_one_section() just assigns ms->section_mem_map
> = 0, which can not be violated by the above changes.
Last night, I got a machine to test this scene. After applying my patch
makedumpfile can still work with v4.4 kernel.
Thanks,
Pingfan
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