netdev - [PATCH] Fix termination state for idr_for_each_entry

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Message-id: <169810161336.20306.1410058490199370047@noble.neil.brown.name>
Date: Tue, 24 Oct 2023 09:53:33 +1100
From: "NeilBrown" <neilb@...e.de>
To: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Cc: LKML <linux-kernel@...r.kernel.org>, Matthew Wilcox <willy@...radead.org>,
 Chris Mi <chrism@...lanox.com>, Cong Wang <xiyou.wangcong@...il.com>
Subject: [PATCH] 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: e33d2b74d805 ("idr: fix overflow case for idr_for_each_entry_ul()")
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Chris Mi <chrism@...lanox.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>
Signed-off-by: NeilBrown <neilb@...e.de>
---
 include/linux/idr.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/idr.h b/include/linux/idr.h
index a0dce14090a9..da5f5fa4a3a6 100644
--- a/include/linux/idr.h
+++ b/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)

 /*
-- 
2.42.0