Re: [Xen-devel] [PATCH 2/2] use return value of domain_adjust_tot_pages() where feasible

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 27/11/13 08:26, Jan Beulich wrote:
> This is generally cheaper than re-reading ->tot_pages.
>
> While doing so I also noticed an improper use (lacking error handling)
> of get_domain() as well as lacks of ->is_dying checks in the memory
> sharing code, which the patch fixes at once. In the course of doing
> this I further noticed other error paths there pointlessly calling
> put_page() et al with ->page_alloc_lock still held, which is also being
> reversed.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

>
> --- a/xen/arch/x86/mm/mem_sharing.c
> +++ b/xen/arch/x86/mm/mem_sharing.c
> @@ -611,9 +611,16 @@ static int page_make_sharable(struct dom
>                         struct page_info *page, 
>                         int expected_refcnt)
>  {
> -    int drop_dom_ref;
> +    bool_t drop_dom_ref;
> +
>      spin_lock(&d->page_alloc_lock);
>  
> +    if ( d->is_dying )
> +    {
> +        spin_unlock(&d->page_alloc_lock);
> +        return -EBUSY;
> +    }
> +
>      /* Change page type and count atomically */
>      if ( !get_page_and_type(page, d, PGT_shared_page) )
>      {
> @@ -624,8 +631,8 @@ static int page_make_sharable(struct dom
>      /* Check it wasn't already sharable and undo if it was */
>      if ( (page->u.inuse.type_info & PGT_count_mask) != 1 )
>      {
> -        put_page_and_type(page);
>          spin_unlock(&d->page_alloc_lock);
> +        put_page_and_type(page);
>          return -EEXIST;
>      }
>  
> @@ -633,15 +640,14 @@ static int page_make_sharable(struct dom
>       * the second from get_page_and_type at the top of this function */
>      if ( page->count_info != (PGC_allocated | (2 + expected_refcnt)) )
>      {
> +        spin_unlock(&d->page_alloc_lock);
>          /* Return type count back to zero */
>          put_page_and_type(page);
> -        spin_unlock(&d->page_alloc_lock);
>          return -E2BIG;
>      }
>  
>      page_set_owner(page, dom_cow);
> -    domain_adjust_tot_pages(d, -1);
> -    drop_dom_ref = (d->tot_pages == 0);
> +    drop_dom_ref = !domain_adjust_tot_pages(d, -1);
>      page_list_del(page, &d->page_list);
>      spin_unlock(&d->page_alloc_lock);
>  
> @@ -659,6 +665,13 @@ static int page_make_private(struct doma
>      
>      spin_lock(&d->page_alloc_lock);
>  
> +    if ( d->is_dying )
> +    {
> +        spin_unlock(&d->page_alloc_lock);
> +        put_page(page);
> +        return -EBUSY;
> +    }
> +
>      /* We can only change the type if count is one */
>      /* Because we are locking pages individually, we need to drop
>       * the lock here, while the page is typed. We cannot risk the 
> @@ -666,8 +679,8 @@ static int page_make_private(struct doma
>      expected_type = (PGT_shared_page | PGT_validated | PGT_locked | 2);
>      if ( page->u.inuse.type_info != expected_type )
>      {
> -        put_page(page);
>          spin_unlock(&d->page_alloc_lock);
> +        put_page(page);
>          return -EEXIST;
>      }
>  
> @@ -682,7 +695,7 @@ static int page_make_private(struct doma
>      page_set_owner(page, d);
>  
>      if ( domain_adjust_tot_pages(d, 1) == 1 )
> -        get_domain(d);
> +        get_knownalive_domain(d);
>      page_list_add_tail(page, &d->page_list);
>      spin_unlock(&d->page_alloc_lock);
>  
> --- a/xen/common/memory.c
> +++ b/xen/common/memory.c
> @@ -475,8 +475,8 @@ static long memory_exchange(XEN_GUEST_HA
>                               (j * (1UL << exch.out.extent_order)));
>  
>                  spin_lock(&d->page_alloc_lock);
> -                domain_adjust_tot_pages(d, -dec_count);
> -                drop_dom_ref = (dec_count && !d->tot_pages);
> +                drop_dom_ref = (dec_count &&
> +                                !domain_adjust_tot_pages(d, -dec_count));
>                  spin_unlock(&d->page_alloc_lock);
>  
>                  if ( drop_dom_ref )
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -1516,8 +1516,9 @@ struct page_info *alloc_domheap_pages(
>  
>  void free_domheap_pages(struct page_info *pg, unsigned int order)
>  {
> -    int            i, drop_dom_ref;
>      struct domain *d = page_get_owner(pg);
> +    unsigned int i;
> +    bool_t drop_dom_ref;
>  
>      ASSERT(!in_irq());
>  
> @@ -1545,8 +1546,7 @@ void free_domheap_pages(struct page_info
>              page_list_del2(&pg[i], &d->page_list, &d->arch.relmem_list);
>          }
>  
> -        domain_adjust_tot_pages(d, -(1 << order));
> -        drop_dom_ref = (d->tot_pages == 0);
> +        drop_dom_ref = !domain_adjust_tot_pages(d, -(1 << order));
>  
>          spin_unlock_recursive(&d->page_alloc_lock);
>  
>
>


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