Fix termination state for idr_for_each_entry_ul()

The comment for idr_for_each_entry_ul() states

  after normal termination @entry is left with the value NULL

This is not correct in the case where UINT_MAX has an entry in the idr.
In that case @entry will be non-NULL after termination.
No current code depends on the documentation being correct, but to
save future code we should fix it.

Also fix idr_for_each_entry_continue_ul().  While this is not documented
as leaving @entry as NULL, the mellanox driver appears to depend on
it doing so.  So make that explicit in the documentation as well as in
the code.

Fixes: e33d2b7 ("idr: fix overflow case for idr_for_each_entry_ul()")
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Chris Mi <chrism@mellanox.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: neilbrown

include/linux/idr.h

@@ -200,7 +200,7 @@ static inline void idr_preload_end(void)
  */
 #define idr_for_each_entry_ul(idr, entry, tmp, id)			\
 	for (tmp = 0, id = 0;						\
-	     tmp <= id && ((entry) = idr_get_next_ul(idr, &(id))) != NULL; \
+	     ((entry) = tmp <= id ? idr_get_next_ul(idr, &(id)) : NULL) != NULL; \
 	     tmp = id, ++id)
 
 /**
@@ -224,10 +224,12 @@ static inline void idr_preload_end(void)
  * @id: Entry ID.
  *
  * Continue to iterate over entries, continuing after the current position.
+ * After normal termination @entry is left with the value NULL.  This
+ * is convenient for a "not found" value.
  */
 #define idr_for_each_entry_continue_ul(idr, entry, tmp, id)		\
 	for (tmp = id;							\
-	     tmp <= id && ((entry) = idr_get_next_ul(idr, &(id))) != NULL; \
+	     ((entry) = tmp <= id ? idr_get_next_ul(idr, &(id)) : NULL) != NULL; \
 	     tmp = id, ++id)
 
 /*