Re: Dmesg not being dumped

[Nikolay Borisov <kernel@kyup.com>]

On 08/19/2015 11:38 PM, Dave Anderson wrote:
> 
> 
> ----- Original Message -----
>>
>> Hi,
>>
>> On 08/19/2015 12:02 PM, Baoquan He wrote:
>>> On 08/19/15 at 09:21am, Nikolay Borisov wrote:
>>>> Hello,
>>>>
>>>> I've recently noticed that when creating crashdumps the dmesg is not
>>>> being saved. The error reported is this: "Missing the struct log size
>>>> export". I've tested with both kernel 4.1.1 and 3.12.28. My version of
>>>> kexec tools is : kexec-tools 2.0.9 released 04 June 2015. The kernel has
>>>> been compiled with debugging info so the respective symbol should be
>>>> exported but apparently it is not. Any ideas how to debug that?
>>>
>>> That would be more helpful if you can attach the 1st kernel and kdump
>>> kernel console log.
>>
>> I just tested with 4.1.6 with the same result. I'm sending you a link to
>> the bzImage in question
>> http://georgi.unixsol.org/cruft/tmp/bzImage-4.1.6-clouder1 ( I assume
>> you meant the bzImage, if you need I can provide the vmlinux as well).
>> Unfortunately, I couldn't figure how to obtain the log of kdump in
>> textual format (and didn't want to send pictures). Here are the 3
>> relevant lines (from memory):
>>
>> Saving vmcore-dmesg.txt
>> Missing the struct log size export   
>> Error saving vmcore-dmesg.txt.
>>
>> Yet, when I load the crashdump inside the 'crash' utility and invoke the
>> 'log' command the dmesg log is there. Whereas the vmcore-dmesg-incomplete.txt is empty.
> 
> FYI -- the crash utility doesn't use the vmcoreinfo data for its "log" command, 
> but you can dump the vmcore's header contents, including the vmcoreinfo strings,
> with the "help -n" command.  For example:

Thanks for the tip, using that I can confirm that the actual symbols are
in the resulting vmcoreinfo:

		      SIZE(printk_log)=16
		      OFFSET(printk_log.ts_nsec)=0
                      OFFSET(printk_log.len)=8
                      OFFSET(printk_log.text_len)=10
                      OFFSET(printk_log.dict_len)=12

So the required symbol is there (printk_log) but for some reason kexec
cannot read it... I tried creating an uncompressed crash (removing the
-c option from the makedumpfile command to no avail)..


> 
> crash> help -n
> ... [ cut ] ...
>                       OSRELEASE=3.18.0-0.rc2.git2.1.slub1.fc21.x86_64
>                       PAGESIZE=4096
>                       SYMBOL(init_uts_ns)=ffffffff81e1b300
>                       SYMBOL(node_online_map)=ffffffff81fe8980
>                       SYMBOL(swapper_pg_dir)=ffffffff81e14000
>                       SYMBOL(_stext)=ffffffff810001c8
>                       SYMBOL(vmap_area_list)=ffffffff81efce50
>                       SYMBOL(mem_section)=ffffffff832eb180
>                       LENGTH(mem_section)=4096
>                       SIZE(mem_section)=32
>                       OFFSET(mem_section.section_mem_map)=0
>                       SIZE(page)=64
>                       SIZE(pglist_data)=156928
>                       SIZE(zone)=1984
>                       SIZE(free_area)=88
>                       SIZE(list_head)=16
>                       SIZE(nodemask_t)=128
>                       OFFSET(page.flags)=0
>                       OFFSET(page._count)=28
>                       OFFSET(page.mapping)=8
>                       OFFSET(page.lru)=32
>                       OFFSET(page._mapcount)=24
>                       OFFSET(page.private)=48
>                       OFFSET(pglist_data.node_zones)=0
>                       OFFSET(pglist_data.nr_zones)=156480
>                       OFFSET(pglist_data.node_start_pfn)=156560
>                       OFFSET(pglist_data.node_spanned_pages)=156576
>                       OFFSET(pglist_data.node_id)=156584
>                       OFFSET(zone.free_area)=392
>                       OFFSET(zone.vm_stat)=1664
>                       OFFSET(zone.spanned_pages)=120
>                       OFFSET(free_area.free_list)=0
>                       OFFSET(list_head.next)=0
>                       OFFSET(list_head.prev)=8
>                       OFFSET(vmap_area.va_start)=0
>                       OFFSET(vmap_area.list)=48
>                       LENGTH(zone.free_area)=11
>                       SYMBOL(log_buf)=ffffffff81e5f0c0
>                       SYMBOL(log_buf_len)=ffffffff81e5f0bc
>                       SYMBOL(log_first_idx)=ffffffff831bee88
>                       SYMBOL(log_next_idx)=ffffffff831bee78
>                       SIZE(printk_log)=16
>                       OFFSET(printk_log.ts_nsec)=0
>                       OFFSET(printk_log.len)=8
>                       OFFSET(printk_log.text_len)=10
>                       OFFSET(printk_log.dict_len)=12
>                       LENGTH(free_area.free_list)=5
>                       NUMBER(NR_FREE_PAGES)=0
>                       NUMBER(PG_lru)=5
>                       NUMBER(PG_private)=11
>                       NUMBER(PG_swapcache)=16
>                       NUMBER(PG_slab)=7
>                       NUMBER(PG_hwpoison)=23
>                       NUMBER(PG_head_mask)=16384
>                       NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE)=-128
>                       SYMBOL(free_huge_page)=ffffffff81239430
>                       SYMBOL(phys_base)=ffffffff81e1b010
>                       SYMBOL(init_level4_pgt)=ffffffff81e14000
>                       SYMBOL(node_data)=ffffffff81fe2d40
>                       LENGTH(node_data)=1024
>                       KERNELOFFSET=0
>                       CRASHTIME=141512763
> ...
> 
> Dave
> 

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