Re: [patch 019/154] mm: make madvise(MADV_WILLNEED) support swap file prefetch

[Sasha Levin <sasha.levin@oracle.com>]

Hi Andrea,

On 12/16/2013 03:52 PM, Andrea Arcangeli wrote:
> Is the bug reproducible? If yes the simplest is probably to add some
> allocation tracking to the page, so if page->ptl is null we can simply
> print a stack trace of who allocated the page (and later forgot to
> initialize the ptl).

Yes, it's easy to reproduce. I've done as suggested and here's the trace from
the allocation:

[  184.139519]  [<ffffffff8107de0f>] save_stack_trace+0x2f/0x50
[  184.140706]  [<ffffffff81257769>] get_page_from_freelist+0x759/0x7a0
[  184.141605]  [<ffffffff81258438>] __alloc_pages_nodemask+0x3b8/0x520
[  184.142810]  [<ffffffff812a4baf>] alloc_pages_vma+0x1df/0x220
[  184.143631]  [<ffffffff812bcd58>] do_huge_pmd_wp_page+0x2d8/0x730
[  184.144526]  [<ffffffff81280e01>] __handle_mm_fault+0x2b1/0x3d0
[  184.145361]  [<ffffffff81281053>] handle_mm_fault+0x133/0x1c0
[  184.146129]  [<ffffffff812815f8>] __get_user_pages+0x448/0x640
[  184.147055]  [<ffffffff812827a4>] __mlock_vma_pages_range+0xd4/0xe0
[  184.147980]  [<ffffffff812828c0>] __mm_populate+0x110/0x190
[  184.148933]  [<ffffffff812839b2>] SyS_mlock+0xf2/0x130
[  184.149689]  [<ffffffff843c5e50>] tracesys+0xdd/0xe2

> Agree with Kirill that it would help to verify the bug goes away by
> disabling USE_SPLIT_PTE_PTLOCKS.

It seems that the bug is gone without USE_SPLIT_PTE_PTLOCKS.


Thanks,
Sasha

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