[PATCH net v2 3/5] ixgbe: xsk: resolve the negative overflow of budget in ixgbe_xmit_zc

[PATCH net v2 3/5] ixgbe: xsk: resolve the negative overflow of budget in ixgbe_xmit_zc

[Tony Nguyen]

From: Jason Xing <kernelxing@tencent.com>

Resolve the budget negative overflow which leads to returning true in
ixgbe_xmit_zc even when the budget of descs are thoroughly consumed.

Before this patch, when the budget is decreased to zero and finishes
sending the last allowed desc in ixgbe_xmit_zc, it will always turn back
and enter into the while() statement to see if it should keep processing
packets, but in the meantime it unexpectedly decreases the value again to
'unsigned int (0--)', namely, UINT_MAX. Finally, the ixgbe_xmit_zc returns
true, showing 'we complete cleaning the budget'. That also means
'clean_complete = true' in ixgbe_poll.

The true theory behind this is if that budget number of descs are consumed,
it implies that we might have more descs to be done. So we should return
false in ixgbe_xmit_zc to tell napi poll to find another chance to start
polling to handle the rest of descs. On the contrary, returning true here
means job done and we know we finish all the possible descs this time and
we don't intend to start a new napi poll.

It is apparently against our expectations. Please also see how
ixgbe_clean_tx_irq() handles the problem: it uses do..while() statement
to make sure the budget can be decreased to zero at most and the negative
overflow never happens.

The patch adds 'likely' because we rarely would not hit the loop condition
since the standard budget is 256.

Fixes: 8221c5eba8c1 ("ixgbe: add AF_XDP zero-copy Tx support")
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Larysa Zaremba <larysa.zaremba@intel.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Priya Singh <priyax.singh@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
---
 drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
index ac58964b2f08..7b941505a9d0 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
@@ -398,7 +398,7 @@ static bool ixgbe_xmit_zc(struct ixgbe_ring *xdp_ring, unsigned int budget)
 	dma_addr_t dma;
 	u32 cmd_type;
 
-	while (budget-- > 0) {
+	while (likely(budget)) {
 		if (unlikely(!ixgbe_desc_unused(xdp_ring))) {
 			work_done = false;
 			break;
@@ -433,6 +433,8 @@ static bool ixgbe_xmit_zc(struct ixgbe_ring *xdp_ring, unsigned int budget)
 		xdp_ring->next_to_use++;
 		if (xdp_ring->next_to_use == xdp_ring->count)
 			xdp_ring->next_to_use = 0;
+
+		budget--;
 	}
 
 	if (tx_desc) {
-- 
2.47.1

[PATCH net v2 4/5] ixgbe: fix ndo_xdp_xmit() workloads

[Tony Nguyen]

From: Maciej Fijalkowski <maciej.fijalkowski@intel.com>

Currently ixgbe driver checks periodically in its watchdog subtask if
there is anything to be transmitted (considering both Tx and XDP rings)
under state of carrier not being 'ok'. Such event is interpreted as Tx
hang and therefore results in interface reset.

This is currently problematic for ndo_xdp_xmit() as it is allowed to
produce descriptors when interface is going through reset or its carrier
is turned off.

Furthermore, XDP rings should not really be objects of Tx hang
detection. This mechanism is rather a matter of ndo_tx_timeout() being
called from dev_watchdog against Tx rings exposed to networking stack.

Taking into account issues described above, let us have a two fold fix -
do not respect XDP rings in local ixgbe watchdog and do not produce Tx
descriptors in ndo_xdp_xmit callback when there is some problem with
carrier currently. For now, keep the Tx hang checks in clean Tx irq
routine, but adjust it to not execute for XDP rings.

Cc: Tobias Böhm <tobias.boehm@hetzner-cloud.de>
Reported-by: Marcus Wichelmann <marcus.wichelmann@hetzner-cloud.de>
Closes: https://lore.kernel.org/netdev/eca1880f-253a-4955-afe6-732d7c6926ee@hetzner-cloud.de/
Fixes: 6453073987ba ("ixgbe: add initial support for xdp redirect")
Fixes: 33fdc82f0883 ("ixgbe: add support for XDP_TX action")
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Marcus Wichelmann <marcus.wichelmann@hetzner-cloud.de>
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
---
 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 34 ++++++-------------
 1 file changed, 11 insertions(+), 23 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 6122a0abb41f..80e6a2ef1350 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -968,10 +968,6 @@ static void ixgbe_update_xoff_rx_lfc(struct ixgbe_adapter *adapter)
 	for (i = 0; i < adapter->num_tx_queues; i++)
 		clear_bit(__IXGBE_HANG_CHECK_ARMED,
 			  &adapter->tx_ring[i]->state);
-
-	for (i = 0; i < adapter->num_xdp_queues; i++)
-		clear_bit(__IXGBE_HANG_CHECK_ARMED,
-			  &adapter->xdp_ring[i]->state);
 }
 
 static void ixgbe_update_xoff_received(struct ixgbe_adapter *adapter)
@@ -1214,7 +1210,7 @@ static void ixgbe_pf_handle_tx_hang(struct ixgbe_ring *tx_ring,
 	struct ixgbe_adapter *adapter = netdev_priv(tx_ring->netdev);
 	struct ixgbe_hw *hw = &adapter->hw;
 
-	e_err(drv, "Detected Tx Unit Hang%s\n"
+	e_err(drv, "Detected Tx Unit Hang\n"
 		   "  Tx Queue             <%d>\n"
 		   "  TDH, TDT             <%x>, <%x>\n"
 		   "  next_to_use          <%x>\n"
@@ -1222,16 +1218,14 @@ static void ixgbe_pf_handle_tx_hang(struct ixgbe_ring *tx_ring,
 		   "tx_buffer_info[next_to_clean]\n"
 		   "  time_stamp           <%lx>\n"
 		   "  jiffies              <%lx>\n",
-	      ring_is_xdp(tx_ring) ? " (XDP)" : "",
 	      tx_ring->queue_index,
 	      IXGBE_READ_REG(hw, IXGBE_TDH(tx_ring->reg_idx)),
 	      IXGBE_READ_REG(hw, IXGBE_TDT(tx_ring->reg_idx)),
 	      tx_ring->next_to_use, next,
 	      tx_ring->tx_buffer_info[next].time_stamp, jiffies);
 
-	if (!ring_is_xdp(tx_ring))
-		netif_stop_subqueue(tx_ring->netdev,
-				    tx_ring->queue_index);
+	netif_stop_subqueue(tx_ring->netdev,
+			    tx_ring->queue_index);
 }
 
 /**
@@ -1451,6 +1445,9 @@ static bool ixgbe_clean_tx_irq(struct ixgbe_q_vector *q_vector,
 				   total_bytes);
 	adapter->tx_ipsec += total_ipsec;
 
+	if (ring_is_xdp(tx_ring))
+		return !!budget;
+
 	if (check_for_tx_hang(tx_ring) && ixgbe_check_tx_hang(tx_ring)) {
 		if (adapter->hw.mac.type == ixgbe_mac_e610)
 			ixgbe_handle_mdd_event(adapter, tx_ring);
@@ -1468,9 +1465,6 @@ static bool ixgbe_clean_tx_irq(struct ixgbe_q_vector *q_vector,
 		return true;
 	}
 
-	if (ring_is_xdp(tx_ring))
-		return !!budget;
-
 #define TX_WAKE_THRESHOLD (DESC_NEEDED * 2)
 	txq = netdev_get_tx_queue(tx_ring->netdev, tx_ring->queue_index);
 	if (!__netif_txq_completed_wake(txq, total_packets, total_bytes,
@@ -7974,12 +7968,9 @@ static void ixgbe_check_hang_subtask(struct ixgbe_adapter *adapter)
 		return;
 
 	/* Force detection of hung controller */
-	if (netif_carrier_ok(adapter->netdev)) {
+	if (netif_carrier_ok(adapter->netdev))
 		for (i = 0; i < adapter->num_tx_queues; i++)
 			set_check_for_tx_hang(adapter->tx_ring[i]);
-		for (i = 0; i < adapter->num_xdp_queues; i++)
-			set_check_for_tx_hang(adapter->xdp_ring[i]);
-	}
 
 	if (!(adapter->flags & IXGBE_FLAG_MSIX_ENABLED)) {
 		/*
@@ -8199,13 +8190,6 @@ static bool ixgbe_ring_tx_pending(struct ixgbe_adapter *adapter)
 			return true;
 	}
 
-	for (i = 0; i < adapter->num_xdp_queues; i++) {
-		struct ixgbe_ring *ring = adapter->xdp_ring[i];
-
-		if (ring->next_to_use != ring->next_to_clean)
-			return true;
-	}
-
 	return false;
 }
 
@@ -11005,6 +10989,10 @@ static int ixgbe_xdp_xmit(struct net_device *dev, int n,
 	if (unlikely(test_bit(__IXGBE_DOWN, &adapter->state)))
 		return -ENETDOWN;
 
+	if (!netif_carrier_ok(adapter->netdev) ||
+	    !netif_running(adapter->netdev))
+		return -ENETDOWN;
+
 	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK))
 		return -EINVAL;
 
-- 
2.47.1