Re: [PATCH] net: stmmac: protect statistics updates with a spinlock

From: Jiri Pirko
Date: Fri Jan 05 2024 - 04:46:13 EST

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In reply to: Petr Tesarik: "[PATCH] net: stmmac: protect statistics updates with a spinlock"
Next in thread: Petr Tesařík: "Re: [PATCH] net: stmmac: protect statistics updates with a spinlock"
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Fri, Jan 05, 2024 at 10:15:56AM CET, petr@xxxxxxxxxxx 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@xxxxxxxxxxx>
>---
> 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.

Rest of the patch looks fine to me.

Reviewed-by: Jiri Pirko <jiri@xxxxxxxxxx>

>
> 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
>
>

Next message: Vincent Donnefort: "[PATCH v10 0/2] Introducing trace buffer mapping by user-space"
Previous message: Yan Zhao: "[PATCH 4/4] KVM: selftests: Set KVM_MEM_NON_COHERENT_DMA as a supported memslot flag"
In reply to: Petr Tesarik: "[PATCH] net: stmmac: protect statistics updates with a spinlock"
Next in thread: Petr Tesařík: "Re: [PATCH] net: stmmac: protect statistics updates with a spinlock"
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