Re: [PATCH] gnttab: lock the left grant table earlier in __gnttab_unmap_common()

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 11/11/13 02:07, Matt Wilson wrote:
> From: Matt Wilson <msw@amazon.com>
>
> Luckily today maptrack_limit never shrinks. But if at some point in
> the future this were to change, checking maptrack_limit without
> holding the grant table spinlock would no longer be safe.
>
> Cc: xen-devel@lists.xenproject.org
> Cc: Keir Fraser <keir@xen.org>
> Cc: Jan Beulich <jbeulich@suse.com>

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

> Cc: Anthony Liguori <aliguori@amazon.com>
> Signed-off-by: Matt Wilson <msw@amazon.com>
> ---
>  xen/common/grant_table.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
> index 21c6a14..ef10ff4 100644
> --- a/xen/common/grant_table.c
> +++ b/xen/common/grant_table.c
> @@ -842,15 +842,16 @@ __gnttab_unmap_common(
>  
>      op->frame = (unsigned long)(op->dev_bus_addr >> PAGE_SHIFT);
>  
> +    spin_lock(&lgt->lock);
>      if ( unlikely(op->handle >= lgt->maptrack_limit) )
>      {
> +        spin_unlock(&lgt->lock);
>          gdprintk(XENLOG_INFO, "Bad handle (%d).\n", op->handle);
>          op->status = GNTST_bad_handle;
>          return;
>      }
>  
>      op->map = &maptrack_entry(lgt, op->handle);
> -    spin_lock(&lgt->lock);
>  
>      if ( unlikely(!op->map->flags) )
>      {