netdev - [PATCH net 5/6] igc: Fix launchtime before start of cycle

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Date: Mon, 10 Jul 2023 09:35:02 -0700
From: Tony Nguyen <anthony.l.nguyen@...el.com>
To: davem@...emloft.net,
	kuba@...nel.org,
	pabeni@...hat.com,
	edumazet@...gle.com,
	netdev@...r.kernel.org
Cc: Florian Kauer <florian.kauer@...utronix.de>,
	anthony.l.nguyen@...el.com,
	kurt@...utronix.de,
	vinicius.gomes@...el.com,
	muhammad.husaini.zulkifli@...el.com,
	tee.min.tan@...ux.intel.com,
	aravindhan.gunasekaran@...el.com,
	sasha.neftin@...el.com,
	Naama Meir <naamax.meir@...ux.intel.com>
Subject: [PATCH net 5/6] igc: Fix launchtime before start of cycle

From: Florian Kauer <florian.kauer@...utronix.de>

It is possible (verified on a running system) that frames are processed
by igc_tx_launchtime with a txtime before the start of the cycle
(baset_est).

However, the result of txtime - baset_est is written into a u32,
leading to a wrap around to a positive number. The following
launchtime > 0 check will only branch to executing launchtime = 0
if launchtime is already 0.

Fix it by using a s32 before checking launchtime > 0.

Fixes: db0b124f02ba ("igc: Enhance Qbv scheduling by using first flag bit")
Signed-off-by: Florian Kauer <florian.kauer@...utronix.de>
Reviewed-by: Kurt Kanzenbach <kurt@...utronix.de>
Tested-by: Naama Meir <naamax.meir@...ux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@...el.com>
---
 drivers/net/ethernet/intel/igc/igc_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 5d24930fed8f..4855caa3bae4 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -1016,7 +1016,7 @@ static __le32 igc_tx_launchtime(struct igc_ring *ring, ktime_t txtime,
 	ktime_t base_time = adapter->base_time;
 	ktime_t now = ktime_get_clocktai();
 	ktime_t baset_est, end_of_cycle;
-	u32 launchtime;
+	s32 launchtime;
 	s64 n;
 
 	n = div64_s64(ktime_sub_ns(now, base_time), cycle_time);
-- 
2.38.1