netdev - [RFC net-next 3/4] net: stmmac: do not use __netif_tx_lock

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Message-Id: <20211210193556.1349090-4-yannick.vignon@oss.nxp.com>
Date:   Fri, 10 Dec 2021 20:35:55 +0100
From:   Yannick Vignon <yannick.vignon@....nxp.com>
To:     Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        netdev@...r.kernel.org, Ong Boon Leong <boon.leong.ong@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jose Abreu <joabreu@...opsys.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Wei Wang <weiwan@...gle.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>, mingkai.hu@....com,
        Joakim Zhang <qiangqing.zhang@....com>,
        sebastien.laveze@....com
Cc:     Yannick Vignon <yannick.vignon@....com>
Subject: [RFC net-next 3/4] net: stmmac: do not use __netif_tx_lock_bh when in NAPI threaded mode

From: Yannick Vignon <yannick.vignon@....com>

In threaded mode, a NAPI instance can not execute concurrently in a
separate context but only in its assigned kernel thread.

Replace the calls to __netif_tx_lock_bh/__netif_tx_unlock_bh by their
non-bh version to avoid disabling BH in that case. This prevents high
priority traffic from being blocked by another piece of code already
running with BH disabled.

Signed-off-by: Yannick Vignon <yannick.vignon@....com>
---
 .../net/ethernet/stmicro/stmmac/stmmac_main.c    | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 8bf24902be3c..2190b40fa92e 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -2481,13 +2481,16 @@ static bool stmmac_xdp_xmit_zc(struct stmmac_priv *priv, u32 queue, u32 budget)
  * @queue: TX queue index
  * Description: it reclaims the transmit resources after transmission completes.
  */
-static int stmmac_tx_clean(struct stmmac_priv *priv, int budget, u32 queue)
+static int stmmac_tx_clean(struct stmmac_priv *priv, int budget, u32 queue, bool is_threaded)
 {
 	struct stmmac_tx_queue *tx_q = &priv->tx_queue[queue];
 	unsigned int bytes_compl = 0, pkts_compl = 0;
 	unsigned int entry, xmits = 0, count = 0;
 
-	__netif_tx_lock_bh(netdev_get_tx_queue(priv->dev, queue));
+	if (is_threaded)
+		__netif_tx_lock(netdev_get_tx_queue(priv->dev, queue), smp_processor_id());
+	else
+		__netif_tx_lock_bh(netdev_get_tx_queue(priv->dev, queue));
 
 	priv->xstats.tx_clean++;
 
@@ -2646,7 +2649,10 @@ static int stmmac_tx_clean(struct stmmac_priv *priv, int budget, u32 queue)
 			      STMMAC_COAL_TIMER(priv->tx_coal_timer[queue]),
 			      HRTIMER_MODE_REL);
 
-	__netif_tx_unlock_bh(netdev_get_tx_queue(priv->dev, queue));
+	if (is_threaded)
+		__netif_tx_unlock(netdev_get_tx_queue(priv->dev, queue));
+	else
+		__netif_tx_unlock_bh(netdev_get_tx_queue(priv->dev, queue));
 
 	/* Combine decisions from TX clean and XSK TX */
 	return max(count, xmits);
@@ -5377,7 +5383,7 @@ static int stmmac_napi_poll_tx(struct napi_struct *napi, int budget)
 
 	priv->xstats.napi_poll++;
 
-	work_done = stmmac_tx_clean(priv, budget, chan);
+	work_done = stmmac_tx_clean(priv, budget, chan, !!napi->thread);
 	work_done = min(work_done, budget);
 
 	if (work_done < budget && napi_complete_done(napi, work_done)) {
@@ -5401,7 +5407,7 @@ static int stmmac_napi_poll_rxtx(struct napi_struct *napi, int budget)
 
 	priv->xstats.napi_poll++;
 
-	tx_done = stmmac_tx_clean(priv, budget, chan);
+	tx_done = stmmac_tx_clean(priv, budget, chan, !!napi->thread);
 	tx_done = min(tx_done, budget);
 
 	rx_done = stmmac_rx_zc(priv, budget, chan);
-- 
2.25.1