Re: [linux-next] khugepaged inconsistent lock state

Sergey Senozhatsky
2015-09-24T04:21:58Z

On (09/23/15 16:22), Kirill A. Shutemov wrote:
[..]
> khugepaged does swap in during collapse under anon_vma lock. It causes
> complain from lockdep. The trace below shows following scenario:
>
> - khugepaged tries to swap in a page under mmap_sem and anon_vma lock;
> - do_swap_page() calls swapin_readahead() with GFP_HIGHUSER_MOVABLE;
> - __read_swap_cache_async() tries to allocate the page for swap in;
> - lockdep_trace_alloc() in __alloc_pages_nodemask() notices that with
> given gfp_mask we could end up in direct relaim.
> - Lockdep already knows that reclaim sometimes (e.g. in case of
> split_huge_page()) wants to take anon_vma lock on its own.
>
> Therefore deadlock is possible.
[..]

Gave it some testing on my box. Works fine on my side.

I guess you can add (if needed)
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

-ss

> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reported-by: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
> ---
> mm/huge_memory.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index dd58ecfcafe6..06c8f6d8fee2 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2725,10 +2725,10 @@ static void collapse_huge_page(struct mm_struct *mm,
> goto out;
> }
>
> - anon_vma_lock_write(vma->anon_vma);
> -
> __collapse_huge_page_swapin(mm, vma, address, pmd);
>
> + anon_vma_lock_write(vma->anon_vma);
> +
> pte = pte_offset_map(pmd, address);
> pte_ptl = pte_lockptr(mm, pmd);
>
> --
> Kirill A. Shutemov
>