[PATCH v4 net 0/4] net: enetc: fix some issues of XDP

[PATCH v4 net 0/4] net: enetc: fix some issues of XDP

[Wei Fang]

We found some bugs when testing the XDP function of enetc driver,
and these bugs are easy to reproduce. This is not only causes XDP
to not work, but also the network cannot be restored after exiting
the XDP program. So the patch set is mainly to fix these bugs. For
details, please see the commit message of each patch.

---
v1 link: https://lore.kernel.org/bpf/20240919084104.661180-1-wei.fang@nxp.com/T/
v2 link: https://lore.kernel.org/netdev/20241008224806.2onzkt3gbslw5jxb@skbuf/T/
v3 link: https://lore.kernel.org/imx/20241009090327.146461-1-wei.fang@nxp.com/T/
---

Wei Fang (4):
  net: enetc: remove xdp_drops statistic from enetc_xdp_drop()
  net: enetc: block concurrent XDP transmissions during ring
    reconfiguration
  net: enetc: disable Tx BD rings after they are empty
  net: enetc: disable NAPI after all rings are disabled

 drivers/net/ethernet/freescale/enetc/enetc.c | 56 +++++++++++++++-----
 drivers/net/ethernet/freescale/enetc/enetc.h |  1 +
 2 files changed, 44 insertions(+), 13 deletions(-)

-- 
2.34.1

[PATCH v4 net 1/4] net: enetc: remove xdp_drops statistic from enetc_xdp_drop()

[Wei Fang]

The xdp_drops statistic indicates the number of XDP frames dropped in
the Rx direction. However, enetc_xdp_drop() is also used in XDP_TX and
XDP_REDIRECT actions. If frame loss occurs in these two actions, the
frames loss count should not be included in xdp_drops, because there
are already xdp_tx_drops and xdp_redirect_failures to count the frame
loss of these two actions, so it's better to remove xdp_drops statistic
from enetc_xdp_drop() and increase xdp_drops in XDP_DROP action.

Fixes: 7ed2bc80074e ("net: enetc: add support for XDP_TX")
Cc: stable@vger.kernel.org
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
v2: no changes
v3: no changes
v4: no changes
---
 drivers/net/ethernet/freescale/enetc/enetc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
index 032d8eadd003..56e59721ec7d 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -1521,7 +1521,6 @@ static void enetc_xdp_drop(struct enetc_bdr *rx_ring, int rx_ring_first,
 				  &rx_ring->rx_swbd[rx_ring_first]);
 		enetc_bdr_idx_inc(rx_ring, &rx_ring_first);
 	}
-	rx_ring->stats.xdp_drops++;
 }
 
 static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring,
@@ -1586,6 +1585,7 @@ static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring,
 			fallthrough;
 		case XDP_DROP:
 			enetc_xdp_drop(rx_ring, orig_i, i);
+			rx_ring->stats.xdp_drops++;
 			break;
 		case XDP_PASS:
 			rxbd = orig_rxbd;
-- 
2.34.1

[PATCH v4 net 2/4] net: enetc: block concurrent XDP transmissions during ring reconfiguration

[Wei Fang]

When testing the XDP_REDIRECT function on the LS1028A platform, we
found a very reproducible issue that the Tx frames can no longer be
sent out even if XDP_REDIRECT is turned off. Specifically, if there
is a lot of traffic on Rx direction, when XDP_REDIRECT is turned on,
the console may display some warnings like "timeout for tx ring #6
clear", and all redirected frames will be dropped, the detailed log
is as follows.

root@ls1028ardb:~# ./xdp-bench redirect eno0 eno2
Redirecting from eno0 (ifindex 3; driver fsl_enetc) to eno2 (ifindex 4; driver fsl_enetc)
[203.849809] fsl_enetc 0000:00:00.2 eno2: timeout for tx ring #5 clear
[204.006051] fsl_enetc 0000:00:00.2 eno2: timeout for tx ring #6 clear
[204.161944] fsl_enetc 0000:00:00.2 eno2: timeout for tx ring #7 clear
eno0->eno2     1420505 rx/s       1420590 err,drop/s      0 xmit/s
  xmit eno0->eno2    0 xmit/s     1420590 drop/s     0 drv_err/s     15.71 bulk-avg
eno0->eno2     1420484 rx/s       1420485 err,drop/s      0 xmit/s
  xmit eno0->eno2    0 xmit/s     1420485 drop/s     0 drv_err/s     15.71 bulk-avg

By analyzing the XDP_REDIRECT implementation of enetc driver, the
driver will reconfigure Tx and Rx BD rings when a bpf program is
installed or uninstalled, but there is no mechanisms to block the
redirected frames when enetc driver reconfigures rings. Similarly,
XDP_TX verdicts on received frames can also lead to frames being
enqueued in the Tx rings. Because XDP ignores the state set by the
netif_tx_wake_queue() API, so introduce the ENETC_TX_DOWN flag to
suppress transmission of XDP frames.

Fixes: c33bfaf91c4c ("net: enetc: set up XDP program under enetc_reconfigure()")
Cc: stable@vger.kernel.org
Signed-off-by: Wei Fang <wei.fang@nxp.com>
---
v2 changes:
Remove a blank line from the end of enetc_disable_tx_bdrs().
v3 changes:
Block the XDP_TX frames when ENETC_TX_DOWN flag is set.
v4 changes:
1. Modify the title and rephrase the commit message.
2. Move the changes of operation order in enect_stop() and
enetc_stop() to a separated patch (patch 3).
---
 drivers/net/ethernet/freescale/enetc/enetc.c | 14 ++++++++++++++
 drivers/net/ethernet/freescale/enetc/enetc.h |  1 +
 2 files changed, 15 insertions(+)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
index 56e59721ec7d..482c44ed9d46 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -902,6 +902,7 @@ static bool enetc_clean_tx_ring(struct enetc_bdr *tx_ring, int napi_budget)
 
 	if (unlikely(tx_frm_cnt && netif_carrier_ok(ndev) &&
 		     __netif_subqueue_stopped(ndev, tx_ring->index) &&
+		     !test_bit(ENETC_TX_DOWN, &priv->flags) &&
 		     (enetc_bd_unused(tx_ring) >= ENETC_TXBDS_MAX_NEEDED))) {
 		netif_wake_subqueue(ndev, tx_ring->index);
 	}
@@ -1377,6 +1378,9 @@ int enetc_xdp_xmit(struct net_device *ndev, int num_frames,
 	int xdp_tx_bd_cnt, i, k;
 	int xdp_tx_frm_cnt = 0;
 
+	if (unlikely(test_bit(ENETC_TX_DOWN, &priv->flags)))
+		return -ENETDOWN;
+
 	enetc_lock_mdio();
 
 	tx_ring = priv->xdp_tx_ring[smp_processor_id()];
@@ -1602,6 +1606,12 @@ static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring,
 			break;
 		case XDP_TX:
 			tx_ring = priv->xdp_tx_ring[rx_ring->index];
+			if (unlikely(test_bit(ENETC_TX_DOWN, &priv->flags))) {
+				enetc_xdp_drop(rx_ring, orig_i, i);
+				tx_ring->stats.xdp_tx_drops++;
+				break;
+			}
+
 			xdp_tx_bd_cnt = enetc_rx_swbd_to_xdp_tx_swbd(xdp_tx_arr,
 								     rx_ring,
 								     orig_i, i);
@@ -2463,6 +2473,8 @@ void enetc_start(struct net_device *ndev)
 	enetc_enable_bdrs(priv);
 
 	netif_tx_start_all_queues(ndev);
+
+	clear_bit(ENETC_TX_DOWN, &priv->flags);
 }
 EXPORT_SYMBOL_GPL(enetc_start);
 
@@ -2520,6 +2532,8 @@ void enetc_stop(struct net_device *ndev)
 	struct enetc_ndev_priv *priv = netdev_priv(ndev);
 	int i;
 
+	set_bit(ENETC_TX_DOWN, &priv->flags);
+
 	netif_tx_stop_all_queues(ndev);
 
 	enetc_disable_bdrs(priv);
diff --git a/drivers/net/ethernet/freescale/enetc/enetc.h b/drivers/net/ethernet/freescale/enetc/enetc.h
index 97524dfa234c..fb7d98d57783 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.h
+++ b/drivers/net/ethernet/freescale/enetc/enetc.h
@@ -325,6 +325,7 @@ enum enetc_active_offloads {
 
 enum enetc_flags_bit {
 	ENETC_TX_ONESTEP_TSTAMP_IN_PROGRESS = 0,
+	ENETC_TX_DOWN,
 };
 
 /* interrupt coalescing modes */
-- 
2.34.1

Re: [PATCH v4 net 2/4] net: enetc: block concurrent XDP transmissions during ring reconfiguration

[Vladimir Oltean]

On Thu, Oct 10, 2024 at 05:20:54PM +0800, Wei Fang wrote:
> When testing the XDP_REDIRECT function on the LS1028A platform, we
> found a very reproducible issue that the Tx frames can no longer be
> sent out even if XDP_REDIRECT is turned off. Specifically, if there
> is a lot of traffic on Rx direction, when XDP_REDIRECT is turned on,
> the console may display some warnings like "timeout for tx ring #6
> clear", and all redirected frames will be dropped, the detailed log
> is as follows.
> 
> root@ls1028ardb:~# ./xdp-bench redirect eno0 eno2
> Redirecting from eno0 (ifindex 3; driver fsl_enetc) to eno2 (ifindex 4; driver fsl_enetc)
> [203.849809] fsl_enetc 0000:00:00.2 eno2: timeout for tx ring #5 clear
> [204.006051] fsl_enetc 0000:00:00.2 eno2: timeout for tx ring #6 clear
> [204.161944] fsl_enetc 0000:00:00.2 eno2: timeout for tx ring #7 clear
> eno0->eno2     1420505 rx/s       1420590 err,drop/s      0 xmit/s
>   xmit eno0->eno2    0 xmit/s     1420590 drop/s     0 drv_err/s     15.71 bulk-avg
> eno0->eno2     1420484 rx/s       1420485 err,drop/s      0 xmit/s
>   xmit eno0->eno2    0 xmit/s     1420485 drop/s     0 drv_err/s     15.71 bulk-avg
> 
> By analyzing the XDP_REDIRECT implementation of enetc driver, the
> driver will reconfigure Tx and Rx BD rings when a bpf program is
> installed or uninstalled, but there is no mechanisms to block the
> redirected frames when enetc driver reconfigures rings. Similarly,
> XDP_TX verdicts on received frames can also lead to frames being
> enqueued in the Tx rings. Because XDP ignores the state set by the
> netif_tx_wake_queue() API, so introduce the ENETC_TX_DOWN flag to
> suppress transmission of XDP frames.
> 
> Fixes: c33bfaf91c4c ("net: enetc: set up XDP program under enetc_reconfigure()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Wei Fang <wei.fang@nxp.com>
> ---

Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>

[PATCH v4 net 3/4] net: enetc: disable Tx BD rings after they are empty

[Wei Fang]

The Tx BD rings are disabled first in enetc_stop() and the driver
waits for them to become empty. This operation is not safe while
the ring is actively transmitting frames, and will cause the ring
to not be empty and hardware exception. As described in the NETC
block guide, software should only disable an active Tx ring after
all pending ring entries have been consumed (i.e. when PI = CI).
Disabling a transmit ring that is actively processing BDs risks
a HW-SW race hazard whereby a hardware resource becomes assigned
to work on one or more ring entries only to have those entries be
removed due to the ring becoming disabled.

When testing XDP_REDIRECT feautre, although all frames were blocked
from being put into Tx rings during ring reconfiguration, the similar
warning log was still encountered:

fsl_enetc 0000:00:00.2 eno2: timeout for tx ring #6 clear
fsl_enetc 0000:00:00.2 eno2: timeout for tx ring #7 clear

The reason is that when there are still unsent frames in the Tx ring,
disabling the Tx ring causes the remaining frames to be unable to be
sent out. And the Tx ring cannot be restored, which means that even
if the xdp program is uninstalled, the Tx frames cannot be sent out
anymore. Therefore, correct the operation order in enect_start() and
enect_stop().

Fixes: ff58fda09096 ("net: enetc: prioritize ability to go down over packet processing")
Cc: stable@vger.kernel.org
Signed-off-by: Wei Fang <wei.fang@nxp.com>
---
v4 changes: new patch
---
 drivers/net/ethernet/freescale/enetc/enetc.c | 36 ++++++++++++++------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
index 482c44ed9d46..52da10f62430 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -2233,18 +2233,24 @@ static void enetc_enable_rxbdr(struct enetc_hw *hw, struct enetc_bdr *rx_ring)
 	enetc_rxbdr_wr(hw, idx, ENETC_RBMR, rbmr);
 }
 
-static void enetc_enable_bdrs(struct enetc_ndev_priv *priv)
+static void enetc_enable_rx_bdrs(struct enetc_ndev_priv *priv)
 {
 	struct enetc_hw *hw = &priv->si->hw;
 	int i;
 
-	for (i = 0; i < priv->num_tx_rings; i++)
-		enetc_enable_txbdr(hw, priv->tx_ring[i]);
-
 	for (i = 0; i < priv->num_rx_rings; i++)
 		enetc_enable_rxbdr(hw, priv->rx_ring[i]);
 }
 
+static void enetc_enable_tx_bdrs(struct enetc_ndev_priv *priv)
+{
+	struct enetc_hw *hw = &priv->si->hw;
+	int i;
+
+	for (i = 0; i < priv->num_tx_rings; i++)
+		enetc_enable_txbdr(hw, priv->tx_ring[i]);
+}
+
 static void enetc_disable_rxbdr(struct enetc_hw *hw, struct enetc_bdr *rx_ring)
 {
 	int idx = rx_ring->index;
@@ -2261,18 +2267,24 @@ static void enetc_disable_txbdr(struct enetc_hw *hw, struct enetc_bdr *rx_ring)
 	enetc_txbdr_wr(hw, idx, ENETC_TBMR, 0);
 }
 
-static void enetc_disable_bdrs(struct enetc_ndev_priv *priv)
+static void enetc_disable_rx_bdrs(struct enetc_ndev_priv *priv)
 {
 	struct enetc_hw *hw = &priv->si->hw;
 	int i;
 
-	for (i = 0; i < priv->num_tx_rings; i++)
-		enetc_disable_txbdr(hw, priv->tx_ring[i]);
-
 	for (i = 0; i < priv->num_rx_rings; i++)
 		enetc_disable_rxbdr(hw, priv->rx_ring[i]);
 }
 
+static void enetc_disable_tx_bdrs(struct enetc_ndev_priv *priv)
+{
+	struct enetc_hw *hw = &priv->si->hw;
+	int i;
+
+	for (i = 0; i < priv->num_tx_rings; i++)
+		enetc_disable_txbdr(hw, priv->tx_ring[i]);
+}
+
 static void enetc_wait_txbdr(struct enetc_hw *hw, struct enetc_bdr *tx_ring)
 {
 	int delay = 8, timeout = 100;
@@ -2462,6 +2474,8 @@ void enetc_start(struct net_device *ndev)
 
 	enetc_setup_interrupts(priv);
 
+	enetc_enable_tx_bdrs(priv);
+
 	for (i = 0; i < priv->bdr_int_num; i++) {
 		int irq = pci_irq_vector(priv->si->pdev,
 					 ENETC_BDR_INT_BASE_IDX + i);
@@ -2470,7 +2484,7 @@ void enetc_start(struct net_device *ndev)
 		enable_irq(irq);
 	}
 
-	enetc_enable_bdrs(priv);
+	enetc_enable_rx_bdrs(priv);
 
 	netif_tx_start_all_queues(ndev);
 
@@ -2536,7 +2550,7 @@ void enetc_stop(struct net_device *ndev)
 
 	netif_tx_stop_all_queues(ndev);
 
-	enetc_disable_bdrs(priv);
+	enetc_disable_rx_bdrs(priv);
 
 	for (i = 0; i < priv->bdr_int_num; i++) {
 		int irq = pci_irq_vector(priv->si->pdev,
@@ -2549,6 +2563,8 @@ void enetc_stop(struct net_device *ndev)
 
 	enetc_wait_bdrs(priv);
 
+	enetc_disable_tx_bdrs(priv);
+
 	enetc_clear_interrupts(priv);
 }
 EXPORT_SYMBOL_GPL(enetc_stop);
-- 
2.34.1

Re: [PATCH v4 net 3/4] net: enetc: disable Tx BD rings after they are empty

[Vladimir Oltean]

On Thu, Oct 10, 2024 at 05:20:55PM +0800, Wei Fang wrote:
> The Tx BD rings are disabled first in enetc_stop() and the driver
> waits for them to become empty. This operation is not safe while
> the ring is actively transmitting frames, and will cause the ring
> to not be empty and hardware exception. As described in the NETC
> block guide, software should only disable an active Tx ring after
> all pending ring entries have been consumed (i.e. when PI = CI).
> Disabling a transmit ring that is actively processing BDs risks
> a HW-SW race hazard whereby a hardware resource becomes assigned
> to work on one or more ring entries only to have those entries be
> removed due to the ring becoming disabled.
> 
> When testing XDP_REDIRECT feautre, although all frames were blocked
> from being put into Tx rings during ring reconfiguration, the similar
> warning log was still encountered:
> 
> fsl_enetc 0000:00:00.2 eno2: timeout for tx ring #6 clear
> fsl_enetc 0000:00:00.2 eno2: timeout for tx ring #7 clear
> 
> The reason is that when there are still unsent frames in the Tx ring,
> disabling the Tx ring causes the remaining frames to be unable to be
> sent out. And the Tx ring cannot be restored, which means that even
> if the xdp program is uninstalled, the Tx frames cannot be sent out
> anymore. Therefore, correct the operation order in enect_start() and
> enect_stop().

Typos, no need to resend for this: enect -> enetc.

> 
> Fixes: ff58fda09096 ("net: enetc: prioritize ability to go down over packet processing")
> Cc: stable@vger.kernel.org
> Signed-off-by: Wei Fang <wei.fang@nxp.com>
> ---

Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>

[PATCH v4 net 4/4] net: enetc: disable NAPI after all rings are disabled

[Wei Fang]

When running "xdp-bench tx eno0" to test the XDP_TX feature of ENETC
on LS1028A, it was found that if the command was re-run multiple times,
Rx could not receive the frames, and the result of xdp-bench showed
that the rx rate was 0.

root@ls1028ardb:~# ./xdp-bench tx eno0
Hairpinning (XDP_TX) packets on eno0 (ifindex 3; driver fsl_enetc)
Summary                      2046 rx/s                  0 err,drop/s
Summary                         0 rx/s                  0 err,drop/s
Summary                         0 rx/s                  0 err,drop/s
Summary                         0 rx/s                  0 err,drop/s

By observing the Rx PIR and CIR registers, CIR is always 0x7FF and
PIR is always 0x7FE, which means that the Rx ring is full and can no
longer accommodate other Rx frames. Therefore, the problem is caused
by the Rx BD ring not being cleaned up.

Further analysis of the code revealed that the Rx BD ring will only
be cleaned if the "cleaned_cnt > xdp_tx_in_flight" condition is met.
Therefore, some debug logs were added to the driver and the current
values of cleaned_cnt and xdp_tx_in_flight were printed when the Rx
BD ring was full. The logs are as follows.

[  178.762419] [XDP TX] >> cleaned_cnt:1728, xdp_tx_in_flight:2140
[  178.771387] [XDP TX] >> cleaned_cnt:1941, xdp_tx_in_flight:2110
[  178.776058] [XDP TX] >> cleaned_cnt:1792, xdp_tx_in_flight:2110

From the results, the max value of xdp_tx_in_flight has reached 2140.
However, the size of the Rx BD ring is only 2048. So xdp_tx_in_flight
did not drop to 0 after enetc_stop() is called and the driver does not
clear it. The root cause is that NAPI is disabled too aggressively,
without having waited for the pending XDP_TX frames to be transmitted,
and their buffers recycled, so that xdp_tx_in_flight cannot naturally
drop to 0. Later, enetc_free_tx_ring() does free those stale, unsent
XDP_TX packets, but it is not coded up to also reset xdp_tx_in_flight,
hence the manifestation of the bug.

One option would be to cover this extra condition in enetc_free_tx_ring(),
but now that the ENETC_TX_DOWN exists, we have created a window at
the beginning of enetc_stop() where NAPI can still be scheduled, but
any concurrent enqueue will be blocked. Therefore, enetc_wait_bdrs()
and enetc_disable_tx_bdrs() can be called with NAPI still scheduled,
and it is guaranteed that this will not wait indefinitely, but instead
give us an indication that the pending TX frames have orderly dropped
to zero. Only then should we call napi_disable().

This way, enetc_free_tx_ring() becomes entirely redundant and can be
dropped as part of subsequent cleanup.

The change also refactors enetc_start() so that it looks like the
mirror opposite procedure of enetc_stop().

Fixes: ff58fda09096 ("net: enetc: prioritize ability to go down over packet processing")
Cc: stable@vger.kernel.org
Signed-off-by: Wei Fang <wei.fang@nxp.com>
---
v2 changes:
1. Modify the titile and rephrase the commit meesage.
2. Use the new solution as described in the title
v3: no changes.
v4 changes:
1. Modify the title and rephrase the commit message.
---
 drivers/net/ethernet/freescale/enetc/enetc.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
index 52da10f62430..c09370eab319 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -2474,8 +2474,6 @@ void enetc_start(struct net_device *ndev)
 
 	enetc_setup_interrupts(priv);
 
-	enetc_enable_tx_bdrs(priv);
-
 	for (i = 0; i < priv->bdr_int_num; i++) {
 		int irq = pci_irq_vector(priv->si->pdev,
 					 ENETC_BDR_INT_BASE_IDX + i);
@@ -2484,6 +2482,8 @@ void enetc_start(struct net_device *ndev)
 		enable_irq(irq);
 	}
 
+	enetc_enable_tx_bdrs(priv);
+
 	enetc_enable_rx_bdrs(priv);
 
 	netif_tx_start_all_queues(ndev);
@@ -2552,6 +2552,10 @@ void enetc_stop(struct net_device *ndev)
 
 	enetc_disable_rx_bdrs(priv);
 
+	enetc_wait_bdrs(priv);
+
+	enetc_disable_tx_bdrs(priv);
+
 	for (i = 0; i < priv->bdr_int_num; i++) {
 		int irq = pci_irq_vector(priv->si->pdev,
 					 ENETC_BDR_INT_BASE_IDX + i);
@@ -2561,10 +2565,6 @@ void enetc_stop(struct net_device *ndev)
 		napi_disable(&priv->int_vector[i]->napi);
 	}
 
-	enetc_wait_bdrs(priv);
-
-	enetc_disable_tx_bdrs(priv);
-
 	enetc_clear_interrupts(priv);
 }
 EXPORT_SYMBOL_GPL(enetc_stop);
-- 
2.34.1

Re: [PATCH v4 net 4/4] net: enetc: disable NAPI after all rings are disabled

[Vladimir Oltean]

On Thu, Oct 10, 2024 at 05:20:56PM +0800, Wei Fang wrote:
> When running "xdp-bench tx eno0" to test the XDP_TX feature of ENETC
> on LS1028A, it was found that if the command was re-run multiple times,
> Rx could not receive the frames, and the result of xdp-bench showed
> that the rx rate was 0.
> 
> root@ls1028ardb:~# ./xdp-bench tx eno0
> Hairpinning (XDP_TX) packets on eno0 (ifindex 3; driver fsl_enetc)
> Summary                      2046 rx/s                  0 err,drop/s
> Summary                         0 rx/s                  0 err,drop/s
> Summary                         0 rx/s                  0 err,drop/s
> Summary                         0 rx/s                  0 err,drop/s
> 
> By observing the Rx PIR and CIR registers, CIR is always 0x7FF and
> PIR is always 0x7FE, which means that the Rx ring is full and can no
> longer accommodate other Rx frames. Therefore, the problem is caused
> by the Rx BD ring not being cleaned up.
> 
> Further analysis of the code revealed that the Rx BD ring will only
> be cleaned if the "cleaned_cnt > xdp_tx_in_flight" condition is met.
> Therefore, some debug logs were added to the driver and the current
> values of cleaned_cnt and xdp_tx_in_flight were printed when the Rx
> BD ring was full. The logs are as follows.
> 
> [  178.762419] [XDP TX] >> cleaned_cnt:1728, xdp_tx_in_flight:2140
> [  178.771387] [XDP TX] >> cleaned_cnt:1941, xdp_tx_in_flight:2110
> [  178.776058] [XDP TX] >> cleaned_cnt:1792, xdp_tx_in_flight:2110
> 
> From the results, the max value of xdp_tx_in_flight has reached 2140.
> However, the size of the Rx BD ring is only 2048. So xdp_tx_in_flight
> did not drop to 0 after enetc_stop() is called and the driver does not
> clear it. The root cause is that NAPI is disabled too aggressively,
> without having waited for the pending XDP_TX frames to be transmitted,
> and their buffers recycled, so that xdp_tx_in_flight cannot naturally
> drop to 0. Later, enetc_free_tx_ring() does free those stale, unsent
> XDP_TX packets, but it is not coded up to also reset xdp_tx_in_flight,
> hence the manifestation of the bug.
> 
> One option would be to cover this extra condition in enetc_free_tx_ring(),
> but now that the ENETC_TX_DOWN exists, we have created a window at
> the beginning of enetc_stop() where NAPI can still be scheduled, but
> any concurrent enqueue will be blocked. Therefore, enetc_wait_bdrs()
> and enetc_disable_tx_bdrs() can be called with NAPI still scheduled,
> and it is guaranteed that this will not wait indefinitely, but instead
> give us an indication that the pending TX frames have orderly dropped
> to zero. Only then should we call napi_disable().
> 
> This way, enetc_free_tx_ring() becomes entirely redundant and can be
> dropped as part of subsequent cleanup.
> 
> The change also refactors enetc_start() so that it looks like the
> mirror opposite procedure of enetc_stop().
> 
> Fixes: ff58fda09096 ("net: enetc: prioritize ability to go down over packet processing")
> Cc: stable@vger.kernel.org
> Signed-off-by: Wei Fang <wei.fang@nxp.com>
> ---
> v2 changes:
> 1. Modify the titile and rephrase the commit meesage.
> 2. Use the new solution as described in the title
> v3: no changes.
> v4 changes:
> 1. Modify the title and rephrase the commit message.
> ---

Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Re: [PATCH v4 net 0/4] net: enetc: fix some issues of XDP

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 10 Oct 2024 17:20:52 +0800 you wrote:
> We found some bugs when testing the XDP function of enetc driver,
> and these bugs are easy to reproduce. This is not only causes XDP
> to not work, but also the network cannot be restored after exiting
> the XDP program. So the patch set is mainly to fix these bugs. For
> details, please see the commit message of each patch.
> 
> 
> [...]

Here is the summary with links:
  - [v4,net,1/4] net: enetc: remove xdp_drops statistic from enetc_xdp_drop()
    https://git.kernel.org/netdev/net/c/412950d5746f
  - [v4,net,2/4] net: enetc: block concurrent XDP transmissions during ring reconfiguration
    https://git.kernel.org/netdev/net/c/c728a95ccf2a
  - [v4,net,3/4] net: enetc: disable Tx BD rings after they are empty
    https://git.kernel.org/netdev/net/c/0a93f2ca4be6
  - [v4,net,4/4] net: enetc: disable NAPI after all rings are disabled
    https://git.kernel.org/netdev/net/c/6b58fadd44aa

You are awesome, thank you!
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