Re: [PATCH] adapt page_lock_anon_vma() to PREEMPT_RCU

[Hugh Dickins <hugh@veritas.com>]

On Sun, 25 Feb 2007, Oleg Nesterov wrote:

> page_lock_anon_vma() uses spin_lock() to block RCU. This doesn't work with
> PREEMPT_RCU, we have to do rcu_read_lock() explicitely. Otherwise, it is
> theoretically possible that slab returns anon_vma's memory to the system
> before we do spin_unlock(&anon_vma->lock).
> 
> Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

Acked-by: Hugh Dickins <hugh@veritas.com>

Thanks for doing this, and sorry for my delay.

Hugh

> 
> --- WQ/mm/rmap.c~	2007-02-18 22:56:49.000000000 +0300
> +++ WQ/mm/rmap.c	2007-02-25 22:43:00.000000000 +0300
> @@ -183,7 +183,7 @@ void __init anon_vma_init(void)
>   */
>  static struct anon_vma *page_lock_anon_vma(struct page *page)
>  {
> -	struct anon_vma *anon_vma = NULL;
> +	struct anon_vma *anon_vma;
>  	unsigned long anon_mapping;
>  
>  	rcu_read_lock();
> @@ -195,9 +195,16 @@ static struct anon_vma *page_lock_anon_v
>  
>  	anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
>  	spin_lock(&anon_vma->lock);
> +	return anon_vma;
>  out:
>  	rcu_read_unlock();
> -	return anon_vma;
> +	return NULL;
> +}
> +
> +static void page_unlock_anon_vma(struct anon_vma *anon_vma)
> +{
> +	spin_unlock(&anon_vma->lock);
> +	rcu_read_unlock();
>  }
>  
>  /*
> @@ -333,7 +340,8 @@ static int page_referenced_anon(struct p
>  		if (!mapcount)
>  			break;
>  	}
> -	spin_unlock(&anon_vma->lock);
> +
> +	page_unlock_anon_vma(anon_vma);
>  	return referenced;
>  }
>  
> @@ -809,7 +817,8 @@ static int try_to_unmap_anon(struct page
>  				!page_mapped(page))
>  			break;
>  	}
> -	spin_unlock(&anon_vma->lock);
> +
> +	page_unlock_anon_vma(anon_vma);
>  	return ret;
>  }
>  
>