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

["Jan Beulich" <JBeulich@xxxxxxxx>]

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. */

Attachment: gnttab-useless-locking.patch
Description: Text document

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