[Crash-utility] makedumpfile: 4.5 kernel commit breaks page filtering

[Atsushi Kumagai]

Hello Dave,

>>Note that PAGE_MAPPING_ANON is now only set in the compound_head page,
>>so when makedumpfile walks though the pages, it will have to look
>>at each page's head page for the bit setting.
>
>Thanks for your report.
>As you said, it seems checking the head page like kernel does is necessary.
>I'll try to work it out, please give me some time.

Reading head page's page->mapping for each tail page will take extra time,
so I contrived another way.

It's just skipping compound tail pages for filtering.
If makedumpfile excludes compound pages, it will be done at a time by
exclude_range() at the time of checking the compound head page. We don't
need to check compound tail pages individually.

I made the patch, could you test the *compound* branch below ?
This version requires a new unexported symbol, you need to specify
-x vmlinux for now.

  https://sourceforge.net/p/makedumpfile/code/ci/compound/tree/


Thanks,
Atsushi Kumagai

>>As it is now, makedumpfile runs amok filtering pages that still have
>>stuff left in page->mapping.  For example, all of the addresses in
>>my "filtered.list" input file are those of legitimate kernel data
>>structures that have been incorrectly filtered because PAGE_MAPPING_ANON
>>(bit 1) has been left set:
>>
>>crash> kmem -p < filtered.list
>>      PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
>>ffffea0011b29040 46ca41000 dead0000ffffffff        0  0 3ffff800000000
>>      PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
>>ffffea0011b29040 46ca41000 dead0000ffffffff        0  0 3ffff800000000
>>      PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
>>ffffea0011b29640 46ca59000 dead0000ffffffff        0  0 3ffff800000000
>>      PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
>>ffffea0011b29640 46ca59000 dead0000ffffffff        0  0 3ffff800000000
>>      PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
>>ffffea0001d51640  75459000 dead0000ffffffff        0  0 1ffff800000000
>>...
>>
>>In earlier kernels, the page->mapping fields above would not have
>>their PAGE_MAPPING_ANON set.
>>
>>Dave
>
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