Re: [Xen-devel] [PATCH RESEND 1/8] gnttab: drop useless locking

[Andrew Cooper]

On 15/08/17 15:38, Jan Beulich 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 

Reviewed-by: Andrew Cooper 

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[Xen-devel] [PATCH RESEND 1/8] gnttab: drop useless locking

[Jan Beulich]

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 

--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -1140,19 +1140,14 @@ __gnttab_unmap_common(
 smp_rmb();
 map = _entry(lgt, op->handle);
 
-grant_read_lock(lgt);
-
 if ( unlikely(!read_atomic(>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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