[Xen-devel] Ping: [PATCH 11/11] gnttab: drop useless locking

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.06.17 at 11:38, <JBeulich@xxxxxxxx> wrote:
> Holding any lock while accessing the maptrack entry fields is
> pointless, as these entries are protected by their associated active
> entry lock (which is being acquired later, before re-validating the
> fields read without holding the lock).
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> --- a/xen/common/grant_table.c
> +++ b/xen/common/grant_table.c
> @@ -1122,19 +1122,14 @@ __gnttab_unmap_common(
>      smp_rmb();
>      map = &maptrack_entry(lgt, op->handle);
>  
> -    grant_read_lock(lgt);
> -
>      if ( unlikely(!read_atomic(&map->flags)) )
>      {
> -        grant_read_unlock(lgt);
>          gdprintk(XENLOG_INFO, "Zero flags for handle %#x\n", op->handle);
>          op->status = GNTST_bad_handle;
>          return;
>      }
>  
>      dom = map->domid;
> -    grant_read_unlock(lgt);
> -
>      if ( unlikely((rd = rcu_lock_domain_by_id(dom)) == NULL) )
>      {
>          /* This can happen when a grant is implicitly unmapped. */




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