netdev - [PATCH v2 ethtool] rxclass: fix a bug in rmgr when searching for empty slot

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Message-Id: <20230901065203.125150-1-yinjun.zhang@corigine.com>
Date: Fri,  1 Sep 2023 14:52:03 +0800
From: Yinjun Zhang <yinjun.zhang@...igine.com>
To: mkubecek@...e.cz
Cc: oss-drivers@...igine.com,
	netdev@...r.kernel.org,
	Yinjun Zhang <yinjun.zhang@...igine.com>,
	Alexander Duyck <alexanderduyck@...a.com>,
	Niklas Söderlund <niklas.soderlund@...igine.com>
Subject: [PATCH v2 ethtool] rxclass: fix a bug in rmgr when searching for empty slot

When reverse searching the list in rmgr for a free location the last
slot (first slot searched) in the list needs special care as it might
not span the full word length. This is done by building a bit-mask
covering the not-active parts of the last word and using that to judge
if there is a free location in the last word or not. Once that is known
searching in the last slot, or to skip it, can be done by the same
algorithm as for the other slots in the list.

There is a bug in creating the bit-mask for the non-active parts of the
last slot where the 0-indexed nature of bit addressing is not taken into
account when shifting. This leads to a one-off bug, fix it.

Fixes: 8d63f72ccdcb ("Add RX packet classification interface")
Signed-off-by: Yinjun Zhang <yinjun.zhang@...igine.com>
Cc: Alexander Duyck <alexanderduyck@...a.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@...igine.com>
---
Change since v1:
Use `loc` instead of `rmgr->size - 1` as suggested by Alexander.
---
 rxclass.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rxclass.c b/rxclass.c
index 66cf00ba7728..f17e3a5124c0 100644
--- a/rxclass.c
+++ b/rxclass.c
@@ -446,7 +446,7 @@ static int rmgr_find_empty_slot(struct rmgr_ctrl *rmgr,
 	 * If loc rolls over it should be greater than or equal to rmgr->size
 	 * and as such we know we have reached the end of the list.
 	 */
-	if (!~(rmgr->slot[slot_num] | (~1UL << rmgr->size % BITS_PER_LONG))) {
+	if (!~(rmgr->slot[slot_num] | (~1UL << loc % BITS_PER_LONG))) {
 		loc -= 1 + (loc % BITS_PER_LONG);
 		slot_num--;
 	}
-- 
2.39.3