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Date: Fri, 5 Jan 2024 11:25:38 +0100
From: Petr =?UTF-8?B?VGVzYcWZw61r?= <petr@tesarici.cz>
To: Jiri Pirko <jiri@resnulli.us>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>, Jose Abreu
 <joabreu@synopsys.com>, "David S. Miller" <davem@davemloft.net>, Eric
 Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>, Paolo
 Abeni <pabeni@redhat.com>, Maxime Coquelin <mcoquelin.stm32@gmail.com>,
 Chen-Yu Tsai <wens@csie.org>, Jernej Skrabec <jernej.skrabec@gmail.com>,
 Samuel Holland <samuel@sholland.org>, "open list:STMMAC ETHERNET DRIVER"
 <netdev@vger.kernel.org>, "moderated list:ARM/STM32 ARCHITECTURE"
 <linux-stm32@st-md-mailman.stormreply.com>, "moderated list:ARM/STM32
 ARCHITECTURE" <linux-arm-kernel@lists.infradead.org>, open list
 <linux-kernel@vger.kernel.org>, "open list:ARM/Allwinner sunXi SoC support"
 <linux-sunxi@lists.linux.dev>
Subject: Re: [PATCH] net: stmmac: protect statistics updates with a spinlock
Message-ID: <20240105112538.319cd522@meshulam.tesarici.cz>
In-Reply-To: <ZZfP0_WHWZ8LFqXX@nanopsycho>
References: <20240105091556.15516-1-petr@tesarici.cz>
	<ZZfP0_WHWZ8LFqXX@nanopsycho>
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On Fri, 5 Jan 2024 10:45:55 +0100
Jiri Pirko <jiri@resnulli.us> wrote:

> Fri, Jan 05, 2024 at 10:15:56AM CET, petr@tesarici.cz wrote:
> >Add a spinlock to fix race conditions while updating Tx/Rx statistics.
> >
> >As explained by a comment in <linux/u64_stats_sync.h>, write side of struct
> >u64_stats_sync must ensure mutual exclusion, or one seqcount update could
> >be lost on 32-bit platforms, thus blocking readers forever.
> >
> >Such lockups have been actually observed on 32-bit Arm after stmmac_xmit()
> >on one core raced with stmmac_napi_poll_tx() on another core.
> >
> >Signed-off-by: Petr Tesarik <petr@tesarici.cz>
> >---
> > drivers/net/ethernet/stmicro/stmmac/common.h  |  2 +
> > .../net/ethernet/stmicro/stmmac/dwmac-sun8i.c |  4 +
> > .../net/ethernet/stmicro/stmmac/dwmac4_lib.c  |  4 +
> > .../net/ethernet/stmicro/stmmac/dwmac_lib.c   |  4 +
> > .../ethernet/stmicro/stmmac/dwxgmac2_dma.c    |  4 +
> > .../net/ethernet/stmicro/stmmac/stmmac_main.c | 80 +++++++++++++------
> > 6 files changed, 72 insertions(+), 26 deletions(-)
> >
> >diff --git a/drivers/net/ethernet/stmicro/stmmac/common.h b/drivers/net/ethernet/stmicro/stmmac/common.h
> >index e3f650e88f82..9a17dfc1055d 100644
> >--- a/drivers/net/ethernet/stmicro/stmmac/common.h
> >+++ b/drivers/net/ethernet/stmicro/stmmac/common.h
> >@@ -70,6 +70,7 @@ struct stmmac_txq_stats {
> > 	u64 tx_tso_frames;
> > 	u64 tx_tso_nfrags;
> > 	struct u64_stats_sync syncp;
> >+	spinlock_t lock;	/* mutual writer exclusion */
> > } ____cacheline_aligned_in_smp;
> > 
> > struct stmmac_rxq_stats {
> >@@ -79,6 +80,7 @@ struct stmmac_rxq_stats {
> > 	u64 rx_normal_irq_n;
> > 	u64 napi_poll;
> > 	struct u64_stats_sync syncp;
> >+	spinlock_t lock;	/* mutual writer exclusion */
> > } ____cacheline_aligned_in_smp;
> > 
> > /* Extra statistic and debug information exposed by ethtool */
> >diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c
> >index 137741b94122..9c568996321d 100644
> >--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c
> >+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-sun8i.c
> >@@ -455,9 +455,11 @@ static int sun8i_dwmac_dma_interrupt(struct stmmac_priv *priv,
> > 
> > 	if (v & EMAC_TX_INT) {
> > 		ret |= handle_tx;
> >+		spin_lock(&txq_stats->lock);
> > 		u64_stats_update_begin(&txq_stats->syncp);
> > 		txq_stats->tx_normal_irq_n++;
> > 		u64_stats_update_end(&txq_stats->syncp);
> >+		spin_unlock(&txq_stats->lock);
> > 	}
> > 
> > 	if (v & EMAC_TX_DMA_STOP_INT)
> >@@ -479,9 +481,11 @@ static int sun8i_dwmac_dma_interrupt(struct stmmac_priv *priv,
> > 
> > 	if (v & EMAC_RX_INT) {
> > 		ret |= handle_rx;
> >+		spin_lock(&rxq_stats->lock);
> > 		u64_stats_update_begin(&rxq_stats->syncp);
> > 		rxq_stats->rx_normal_irq_n++;
> > 		u64_stats_update_end(&rxq_stats->syncp);
> >+		spin_unlock(&rxq_stats->lock);
> > 	}
> > 
> > 	if (v & EMAC_RX_BUF_UA_INT)
> >diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_lib.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_lib.c
> >index 9470d3fd2ded..e50e8b07724b 100644
> >--- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_lib.c
> >+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_lib.c
> >@@ -201,15 +201,19 @@ int dwmac4_dma_interrupt(struct stmmac_priv *priv, void __iomem *ioaddr,
> > 	}
> > 	/* TX/RX NORMAL interrupts */
> > 	if (likely(intr_status & DMA_CHAN_STATUS_RI)) {
> >+		spin_lock(&rxq_stats->lock);
> > 		u64_stats_update_begin(&rxq_stats->syncp);
> > 		rxq_stats->rx_normal_irq_n++;
> > 		u64_stats_update_end(&rxq_stats->syncp);
> >+		spin_unlock(&rxq_stats->lock);
> > 		ret |= handle_rx;
> > 	}
> > 	if (likely(intr_status & DMA_CHAN_STATUS_TI)) {
> >+		spin_lock(&txq_stats->lock);
> > 		u64_stats_update_begin(&txq_stats->syncp);
> > 		txq_stats->tx_normal_irq_n++;
> > 		u64_stats_update_end(&txq_stats->syncp);
> >+		spin_unlock(&txq_stats->lock);
> > 		ret |= handle_tx;
> > 	}
> > 
> >diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac_lib.c b/drivers/net/ethernet/stmicro/stmmac/dwmac_lib.c
> >index 7907d62d3437..a43396a7f852 100644
> >--- a/drivers/net/ethernet/stmicro/stmmac/dwmac_lib.c
> >+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac_lib.c
> >@@ -215,16 +215,20 @@ int dwmac_dma_interrupt(struct stmmac_priv *priv, void __iomem *ioaddr,
> > 			u32 value = readl(ioaddr + DMA_INTR_ENA);
> > 			/* to schedule NAPI on real RIE event. */
> > 			if (likely(value & DMA_INTR_ENA_RIE)) {
> >+				spin_lock(&rxq_stats->lock);
> > 				u64_stats_update_begin(&rxq_stats->syncp);
> > 				rxq_stats->rx_normal_irq_n++;
> > 				u64_stats_update_end(&rxq_stats->syncp);
> >+				spin_unlock(&rxq_stats->lock);
> > 				ret |= handle_rx;
> > 			}
> > 		}
> > 		if (likely(intr_status & DMA_STATUS_TI)) {
> >+			spin_lock(&txq_stats->lock);
> > 			u64_stats_update_begin(&txq_stats->syncp);
> > 			txq_stats->tx_normal_irq_n++;
> > 			u64_stats_update_end(&txq_stats->syncp);
> >+			spin_unlock(&txq_stats->lock);
> > 			ret |= handle_tx;
> > 		}
> > 		if (unlikely(intr_status & DMA_STATUS_ERI))
> >diff --git a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
> >index 3cde695fec91..f4e01436d4cc 100644
> >--- a/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
> >+++ b/drivers/net/ethernet/stmicro/stmmac/dwxgmac2_dma.c
> >@@ -367,15 +367,19 @@ static int dwxgmac2_dma_interrupt(struct stmmac_priv *priv,
> > 	/* TX/RX NORMAL interrupts */
> > 	if (likely(intr_status & XGMAC_NIS)) {
> > 		if (likely(intr_status & XGMAC_RI)) {
> >+			spin_lock(&rxq_stats->lock);
> > 			u64_stats_update_begin(&rxq_stats->syncp);
> > 			rxq_stats->rx_normal_irq_n++;
> > 			u64_stats_update_end(&rxq_stats->syncp);
> >+			spin_unlock(&rxq_stats->lock);
> > 			ret |= handle_rx;
> > 		}
> > 		if (likely(intr_status & (XGMAC_TI | XGMAC_TBU))) {
> >+			spin_lock(&txq_stats->lock);
> > 			u64_stats_update_begin(&txq_stats->syncp);
> > 			txq_stats->tx_normal_irq_n++;
> > 			u64_stats_update_end(&txq_stats->syncp);
> >+			spin_unlock(&txq_stats->lock);
> > 			ret |= handle_tx;
> > 		}
> > 	}
> >diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> >index 37e64283f910..82d8db04d0d1 100644
> >--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> >+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> >@@ -2515,9 +2515,11 @@ static bool stmmac_xdp_xmit_zc(struct stmmac_priv *priv, u32 queue, u32 budget)
> > 		tx_q->cur_tx = STMMAC_GET_ENTRY(tx_q->cur_tx, priv->dma_conf.dma_tx_size);
> > 		entry = tx_q->cur_tx;
> > 	}
> >-	flags = u64_stats_update_begin_irqsave(&txq_stats->syncp);
> >+	spin_lock_irqsave(&txq_stats->lock, flags);
> >+	u64_stats_update_begin(&txq_stats->syncp);
> > 	txq_stats->tx_set_ic_bit += tx_set_ic_bit;
> >-	u64_stats_update_end_irqrestore(&txq_stats->syncp, flags);
> >+	u64_stats_update_end(&txq_stats->syncp);
> >+	spin_unlock_irqrestore(&txq_stats->lock, flags);
> > 
> > 	if (tx_desc) {
> > 		stmmac_flush_tx_descriptors(priv, queue);
> >@@ -2721,11 +2723,13 @@ static int stmmac_tx_clean(struct stmmac_priv *priv, int budget, u32 queue,
> > 	if (tx_q->dirty_tx != tx_q->cur_tx)
> > 		*pending_packets = true;
> > 
> >-	flags = u64_stats_update_begin_irqsave(&txq_stats->syncp);
> >+	spin_lock_irqsave(&txq_stats->lock, flags);
> >+	u64_stats_update_begin(&txq_stats->syncp);
> > 	txq_stats->tx_packets += tx_packets;
> > 	txq_stats->tx_pkt_n += tx_packets;
> > 	txq_stats->tx_clean++;
> >-	u64_stats_update_end_irqrestore(&txq_stats->syncp, flags);
> >+	u64_stats_update_end(&txq_stats->syncp);
> >+	spin_unlock_irqrestore(&txq_stats->lock, flags);
> > 
> > 	priv->xstats.tx_errors += tx_errors;
> > 
> >@@ -4311,13 +4315,15 @@ static netdev_tx_t stmmac_tso_xmit(struct sk_buff *skb, struct net_device *dev)
> > 		netif_tx_stop_queue(netdev_get_tx_queue(priv->dev, queue));
> > 	}
> > 
> >-	flags = u64_stats_update_begin_irqsave(&txq_stats->syncp);
> >+	spin_lock_irqsave(&txq_stats->lock, flags);
> >+	u64_stats_update_begin(&txq_stats->syncp);
> > 	txq_stats->tx_bytes += skb->len;
> > 	txq_stats->tx_tso_frames++;
> > 	txq_stats->tx_tso_nfrags += nfrags;
> > 	if (set_ic)
> > 		txq_stats->tx_set_ic_bit++;
> >-	u64_stats_update_end_irqrestore(&txq_stats->syncp, flags);
> >+	u64_stats_update_end(&txq_stats->syncp);
> >+	spin_unlock_irqrestore(&txq_stats->lock, flags);
> > 
> > 	if (priv->sarc_type)
> > 		stmmac_set_desc_sarc(priv, first, priv->sarc_type);
> >@@ -4560,11 +4566,13 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
> > 		netif_tx_stop_queue(netdev_get_tx_queue(priv->dev, queue));
> > 	}
> > 
> >-	flags = u64_stats_update_begin_irqsave(&txq_stats->syncp);
> >+	spin_lock_irqsave(&txq_stats->lock, flags);
> >+	u64_stats_update_begin(&txq_stats->syncp);
> > 	txq_stats->tx_bytes += skb->len;
> > 	if (set_ic)
> > 		txq_stats->tx_set_ic_bit++;
> >-	u64_stats_update_end_irqrestore(&txq_stats->syncp, flags);
> >+	u64_stats_update_end(&txq_stats->syncp);
> >+	spin_unlock_irqrestore(&txq_stats->lock, flags);
> > 
> > 	if (priv->sarc_type)
> > 		stmmac_set_desc_sarc(priv, first, priv->sarc_type);
> >@@ -4831,9 +4839,11 @@ static int stmmac_xdp_xmit_xdpf(struct stmmac_priv *priv, int queue,
> > 		unsigned long flags;
> > 		tx_q->tx_count_frames = 0;
> > 		stmmac_set_tx_ic(priv, tx_desc);
> >-		flags = u64_stats_update_begin_irqsave(&txq_stats->syncp);
> >+		spin_lock_irqsave(&txq_stats->lock, flags);
> >+		u64_stats_update_begin(&txq_stats->syncp);
> > 		txq_stats->tx_set_ic_bit++;
> >-		u64_stats_update_end_irqrestore(&txq_stats->syncp, flags);
> >+		u64_stats_update_end(&txq_stats->syncp);
> >+		spin_unlock_irqrestore(&txq_stats->lock, flags);
> > 	}
> > 
> > 	stmmac_enable_dma_transmission(priv, priv->ioaddr);
> >@@ -5008,10 +5018,12 @@ static void stmmac_dispatch_skb_zc(struct stmmac_priv *priv, u32 queue,
> > 	skb_record_rx_queue(skb, queue);
> > 	napi_gro_receive(&ch->rxtx_napi, skb);
> > 
> >-	flags = u64_stats_update_begin_irqsave(&rxq_stats->syncp);
> >+	spin_lock_irqsave(&rxq_stats->lock, flags);
> >+	u64_stats_update_begin(&rxq_stats->syncp);
> > 	rxq_stats->rx_pkt_n++;
> > 	rxq_stats->rx_bytes += len;
> >-	u64_stats_update_end_irqrestore(&rxq_stats->syncp, flags);
> >+	u64_stats_update_end(&rxq_stats->syncp);
> >+	spin_unlock_irqrestore(&rxq_stats->lock, flags);
> > }
> > 
> > static bool stmmac_rx_refill_zc(struct stmmac_priv *priv, u32 queue, u32 budget)
> >@@ -5248,9 +5260,11 @@ static int stmmac_rx_zc(struct stmmac_priv *priv, int limit, u32 queue)
> > 
> > 	stmmac_finalize_xdp_rx(priv, xdp_status);
> > 
> >-	flags = u64_stats_update_begin_irqsave(&rxq_stats->syncp);
> >+	spin_lock_irqsave(&rxq_stats->lock, flags);
> >+	u64_stats_update_begin(&rxq_stats->syncp);
> > 	rxq_stats->rx_pkt_n += count;
> >-	u64_stats_update_end_irqrestore(&rxq_stats->syncp, flags);
> >+	u64_stats_update_end(&rxq_stats->syncp);
> >+	spin_unlock_irqrestore(&rxq_stats->lock, flags);
> > 
> > 	priv->xstats.rx_dropped += rx_dropped;
> > 	priv->xstats.rx_errors += rx_errors;
> >@@ -5541,11 +5555,13 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
> > 
> > 	stmmac_rx_refill(priv, queue);
> > 
> >-	flags = u64_stats_update_begin_irqsave(&rxq_stats->syncp);
> >+	spin_lock_irqsave(&rxq_stats->lock, flags);
> >+	u64_stats_update_begin(&rxq_stats->syncp);
> > 	rxq_stats->rx_packets += rx_packets;
> > 	rxq_stats->rx_bytes += rx_bytes;
> > 	rxq_stats->rx_pkt_n += count;
> >-	u64_stats_update_end_irqrestore(&rxq_stats->syncp, flags);
> >+	u64_stats_update_end(&rxq_stats->syncp);
> >+	spin_unlock_irqrestore(&rxq_stats->lock, flags);
> > 
> > 	priv->xstats.rx_dropped += rx_dropped;
> > 	priv->xstats.rx_errors += rx_errors;
> >@@ -5564,9 +5580,11 @@ static int stmmac_napi_poll_rx(struct napi_struct *napi, int budget)
> > 	int work_done;
> > 
> > 	rxq_stats = &priv->xstats.rxq_stats[chan];
> >-	flags = u64_stats_update_begin_irqsave(&rxq_stats->syncp);
> >+	spin_lock_irqsave(&rxq_stats->lock, flags);
> >+	u64_stats_update_begin(&rxq_stats->syncp);
> > 	rxq_stats->napi_poll++;
> >-	u64_stats_update_end_irqrestore(&rxq_stats->syncp, flags);
> >+	u64_stats_update_end(&rxq_stats->syncp);
> >+	spin_unlock_irqrestore(&rxq_stats->lock, flags);
> > 
> > 	work_done = stmmac_rx(priv, budget, chan);
> > 	if (work_done < budget && napi_complete_done(napi, work_done)) {
> >@@ -5592,9 +5610,11 @@ static int stmmac_napi_poll_tx(struct napi_struct *napi, int budget)
> > 	int work_done;
> > 
> > 	txq_stats = &priv->xstats.txq_stats[chan];
> >-	flags = u64_stats_update_begin_irqsave(&txq_stats->syncp);
> >+	spin_lock_irqsave(&txq_stats->lock, flags);
> >+	u64_stats_update_begin(&txq_stats->syncp);
> > 	txq_stats->napi_poll++;
> >-	u64_stats_update_end_irqrestore(&txq_stats->syncp, flags);
> >+	u64_stats_update_end(&txq_stats->syncp);
> >+	spin_unlock_irqrestore(&txq_stats->lock, flags);
> > 
> > 	work_done = stmmac_tx_clean(priv, budget, chan, &pending_packets);
> > 	work_done = min(work_done, budget);
> >@@ -5627,14 +5647,18 @@ static int stmmac_napi_poll_rxtx(struct napi_struct *napi, int budget)
> > 	unsigned long flags;
> > 
> > 	rxq_stats = &priv->xstats.rxq_stats[chan];
> >-	flags = u64_stats_update_begin_irqsave(&rxq_stats->syncp);
> >+	spin_lock_irqsave(&rxq_stats->lock, flags);
> >+	u64_stats_update_begin(&rxq_stats->syncp);
> > 	rxq_stats->napi_poll++;
> >-	u64_stats_update_end_irqrestore(&rxq_stats->syncp, flags);
> >+	u64_stats_update_end(&rxq_stats->syncp);
> >+	spin_unlock(&rxq_stats->lock);  
> 
> Nitpick:
> I know that the original code does that, but any idea why
> u64_stats_update_end_irqrestore() is called here when
> u64_stats_update_begin_irqsave() is called 2 lines below?
> IIUC, this could be one critical section. Could you perhaps merge these
> while at it? Could be a follow-up patch.

I have merged the interrupt disable/enable, but there are two separate
spinlocks for rxq_stats (added to struct stmmac_txq_stats) and for
txq_stats (added to struct stmmac_rxq_stats), so they cannot be merged.

Alternatively, I could use the channel lock to protect stats updates,
but that could increase contention of that lock. I believe more
granularity is better, especially if it does not cost anything: There
is plenty of unused space in struct stmmac_txq_stats and struct
stmmac_rxq_stats (they are both cache-aligned).

Petr T

> 
> Rest of the patch looks fine to me.
> 
> Reviewed-by: Jiri Pirko <jiri@nvidia.com>
> 
> 
> > 
> > 	txq_stats = &priv->xstats.txq_stats[chan];
> >-	flags = u64_stats_update_begin_irqsave(&txq_stats->syncp);
> >+	spin_lock(&txq_stats->lock);
> >+	u64_stats_update_begin(&txq_stats->syncp);
> > 	txq_stats->napi_poll++;
> >-	u64_stats_update_end_irqrestore(&txq_stats->syncp, flags);
> >+	u64_stats_update_end(&txq_stats->syncp);
> >+	spin_unlock_irqrestore(&txq_stats->lock, flags);
> > 
> > 	tx_done = stmmac_tx_clean(priv, budget, chan, &tx_pending_packets);
> > 	tx_done = min(tx_done, budget);
> >@@ -7371,10 +7395,14 @@ int stmmac_dvr_probe(struct device *device,
> > 	priv->device = device;
> > 	priv->dev = ndev;
> > 
> >-	for (i = 0; i < MTL_MAX_RX_QUEUES; i++)
> >+	for (i = 0; i < MTL_MAX_RX_QUEUES; i++) {
> > 		u64_stats_init(&priv->xstats.rxq_stats[i].syncp);
> >-	for (i = 0; i < MTL_MAX_TX_QUEUES; i++)
> >+		spin_lock_init(&priv->xstats.rxq_stats[i].lock);
> >+	}
> >+	for (i = 0; i < MTL_MAX_TX_QUEUES; i++) {
> > 		u64_stats_init(&priv->xstats.txq_stats[i].syncp);
> >+		spin_lock_init(&priv->xstats.txq_stats[i].lock);
> >+	}
> > 
> > 	stmmac_set_ethtool_ops(ndev);
> > 	priv->pause = pause;
> >-- 
> >2.43.0
> >
> >