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Message-ID: <074a9a19-9050-44dd-a0bf-536ae8318da2@kernel.org>
Date: Fri, 2 May 2025 09:14:43 +0200
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Meghana Malladi <m-malladi@...com>, dan.carpenter@...aro.org,
john.fastabend@...il.com, daniel@...earbox.net, ast@...nel.org,
pabeni@...hat.com, kuba@...nel.org, edumazet@...gle.com,
davem@...emloft.net, andrew+netdev@...n.ch
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, srk@...com,
Vignesh Raghavendra <vigneshr@...com>, Roger Quadros <rogerq@...nel.org>,
danishanwar@...com
Subject: Re: [PATCH net 4/4] net: ti: icssg-prueth: Fix kernel panic during
concurrent Tx queue access
On 28/04/2025 14.04, Meghana Malladi wrote:
> Add __netif_tx_lock() to ensure that only one packet is being
> transmitted at a time to avoid race conditions in the netif_txq
> struct and prevent packet data corruption. Failing to do so causes
> kernel panic with the following error:
>
> [ 2184.746764] ------------[ cut here ]------------
> [ 2184.751412] kernel BUG at lib/dynamic_queue_limits.c:99!
> [ 2184.756728] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
>
> logs: https://gist.github.com/MeghanaMalladiTI/9c7aa5fc3b7fb03f87c74aad487956e9
>
> The lock is acquired before calling emac_xmit_xdp_frame() and released after the
> call returns. This ensures that the TX queue is protected from concurrent access
> during the transmission of XDP frames.
>
> Fixes: 62aa3246f462 ("net: ti: icssg-prueth: Add XDP support")
> Signed-off-by: Meghana Malladi <m-malladi@...com>
> ---
> drivers/net/ethernet/ti/icssg/icssg_common.c | 7 ++++++-
> drivers/net/ethernet/ti/icssg/icssg_prueth.c | 7 ++++++-
> 2 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/ethernet/ti/icssg/icssg_common.c b/drivers/net/ethernet/ti/icssg/icssg_common.c
> index a120ff6fec8f..e509b6ff81e7 100644
> --- a/drivers/net/ethernet/ti/icssg/icssg_common.c
> +++ b/drivers/net/ethernet/ti/icssg/icssg_common.c
> @@ -660,6 +660,8 @@ static u32 emac_run_xdp(struct prueth_emac *emac, struct xdp_buff *xdp,
> struct page *page, u32 *len)
> {
> struct net_device *ndev = emac->ndev;
> + struct netdev_queue *netif_txq;
> + int cpu = smp_processor_id();
> struct bpf_prog *xdp_prog;
> struct xdp_frame *xdpf;
> u32 pkt_len = *len;
> @@ -679,8 +681,11 @@ static u32 emac_run_xdp(struct prueth_emac *emac, struct xdp_buff *xdp,
> goto drop;
> }
>
> - q_idx = smp_processor_id() % emac->tx_ch_num;
> + q_idx = cpu % emac->tx_ch_num;
> + netif_txq = netdev_get_tx_queue(ndev, q_idx);
> + __netif_tx_lock(netif_txq, cpu);
> result = emac_xmit_xdp_frame(emac, xdpf, page, q_idx);
> + __netif_tx_unlock(netif_txq);
> if (result == ICSSG_XDP_CONSUMED) {
> ndev->stats.tx_dropped++;
> goto drop;
> diff --git a/drivers/net/ethernet/ti/icssg/icssg_prueth.c b/drivers/net/ethernet/ti/icssg/icssg_prueth.c
> index ee35fecf61e7..b31060e7f698 100644
> --- a/drivers/net/ethernet/ti/icssg/icssg_prueth.c
> +++ b/drivers/net/ethernet/ti/icssg/icssg_prueth.c
> @@ -1075,20 +1075,25 @@ static int emac_xdp_xmit(struct net_device *dev, int n, struct xdp_frame **frame
> {
> struct prueth_emac *emac = netdev_priv(dev);
> struct net_device *ndev = emac->ndev;
> + struct netdev_queue *netif_txq;
> + int cpu = smp_processor_id();
> struct xdp_frame *xdpf;
> unsigned int q_idx;
> int nxmit = 0;
> u32 err;
> int i;
>
> - q_idx = smp_processor_id() % emac->tx_ch_num;
> + q_idx = cpu % emac->tx_ch_num;
> + netif_txq = netdev_get_tx_queue(ndev, q_idx);
>
> if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK))
> return -EINVAL;
>
> for (i = 0; i < n; i++) {
> xdpf = frames[i];
> + __netif_tx_lock(netif_txq, cpu);
> err = emac_xmit_xdp_frame(emac, xdpf, NULL, q_idx);
> + __netif_tx_unlock(netif_txq);
Why are you taking and releasing this lock in a loop?
XDP gain performance by sending a batch of 'n' packets.
This approach looks like a performance killer.
> if (err != ICSSG_XDP_TX) {
> ndev->stats.tx_dropped++;
> break;
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