diff mbox

[11/11] gnttab: drop useless locking

Message ID 594A5ABE02000078001650C2@prv-mh.provo.novell.com (mailing list archive)
State New, archived
Headers show

Commit Message

Jan Beulich June 21, 2017, 9:38 a.m. UTC 
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@suse.com>
gnttab: drop useless locking

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@suse.com>

--- 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. */

Comments

Jan Beulich July 14, 2017, 12:34 p.m. UTC | #1 
>>> On 21.06.17 at 11:38, <JBeulich@suse.com> 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@suse.com>
> 
> --- 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. */
diff mbox

Patch

--- 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. */