As a general library routine, it should behave as efficiently as
possible, even if at present no significant contention is known here.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- a/xen/common/rangeset.c
+++ b/xen/common/rangeset.c
@@ -25,7 +25,7 @@ struct rangeset {
 
     /* Ordered list of ranges contained in this set, and protecting lock. */
     struct list_head range_list;
-    spinlock_t       lock;
+    rwlock_t         lock;
 
     /* Pretty-printing name. */
     char             name[32];
@@ -103,7 +103,7 @@ int rangeset_add_range(
 
     ASSERT(s <= e);
 
-    spin_lock(&r->lock);
+    write_lock(&r->lock);
 
     x = find_range(r, s);
     y = find_range(r, e);
@@ -159,7 +159,7 @@ int rangeset_add_range(
     }
 
  out:
-    spin_unlock(&r->lock);
+    write_unlock(&r->lock);
     return rc;
 }
 
@@ -175,7 +175,7 @@ int rangeset_remove_range(
 
     ASSERT(s <= e);
 
-    spin_lock(&r->lock);
+    write_lock(&r->lock);
 
     x = find_range(r, s);
     y = find_range(r, e);
@@ -231,7 +231,7 @@ int rangeset_remove_range(
     }
 
  out:
-    spin_unlock(&r->lock);
+    write_unlock(&r->lock);
     return rc;
 }
 
@@ -243,10 +243,10 @@ int rangeset_contains_range(
 
     ASSERT(s <= e);
 
-    spin_lock(&r->lock);
+    read_lock(&r->lock);
     x = find_range(r, s);
     contains = (x && (x->e >= e));
-    spin_unlock(&r->lock);
+    read_unlock(&r->lock);
 
     return contains;
 }
@@ -259,10 +259,10 @@ int rangeset_overlaps_range(
 
     ASSERT(s <= e);
 
-    spin_lock(&r->lock);
+    read_lock(&r->lock);
     x = find_range(r, e);
     overlaps = (x && (s <= x->e));
-    spin_unlock(&r->lock);
+    read_unlock(&r->lock);
 
     return overlaps;
 }
@@ -274,13 +274,13 @@ int rangeset_report_ranges(
     struct range *x;
     int rc = 0;
 
-    spin_lock(&r->lock);
+    read_lock(&r->lock);
 
     for ( x = find_range(r, s); x && (x->s <= e) && !rc; x = next_range(r, x) )
         if ( x->e >= s )
             rc = cb(max(x->s, s), min(x->e, e), ctxt);
 
-    spin_unlock(&r->lock);
+    read_unlock(&r->lock);
 
     return rc;
 }
@@ -318,7 +318,7 @@ struct rangeset *rangeset_new(
     if ( r == NULL )
         return NULL;
 
-    spin_lock_init(&r->lock);
+    rwlock_init(&r->lock);
     INIT_LIST_HEAD(&r->range_list);
 
     BUG_ON(flags & ~RANGESETF_prettyprint_hex);
@@ -403,7 +403,7 @@ void rangeset_printk(
     int nr_printed = 0;
     struct range *x;
 
-    spin_lock(&r->lock);
+    read_lock(&r->lock);
 
     printk("%-10s {", r->name);
 
@@ -422,7 +422,7 @@ void rangeset_printk(
 
     printk(" }");
 
-    spin_unlock(&r->lock);
+    read_unlock(&r->lock);
 }
 
 void rangeset_domain_printk(