Re: [linux-next] khugepaged inconsistent lock state

[Sergey Senozhatsky]

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@xxxxxxxxx>

	-ss

> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Reported-by: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
> ---
>  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
> 
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