Re: [REGRESSION] [PATCH net-next v5 2/2] net: stmmac: use per-queue 64 bit statistics where necessary

[Uwe Kleine-König]

Hello,

On Tue, Sep 12, 2023 at 11:04:16AM +0200, Lucas Stach wrote:
> Am Dienstag, dem 12.09.2023 um 16:01 +0800 schrieb Jisheng Zhang:
> > On Mon, Sep 11, 2023 at 07:11:02PM +0200, Uwe Kleine-König wrote:
> > > Hello,
> > > 
> > > this patch became commit 133466c3bbe171f826294161db203f7670bb30c8 and is
> > > part of v6.6-rc1.
> > > 
> > > On my arm/stm32mp157 based machine using NFS root this commit makes the
> > > following appear in the kernel log:
> > > 
> > > 	INFO: trying to register non-static key.
> > > 	The code is fine but needs lockdep annotation, or maybe
> > > 	you didn't initialize this object before use?
> > > 	turning off the locking correctness validator.
> > > 	CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc1-00449-g133466c3bbe1-dirty #21
> > > 	Hardware name: STM32 (Device Tree Support)
> > > 	 unwind_backtrace from show_stack+0x18/0x1c
> > > 	 show_stack from dump_stack_lvl+0x60/0x90
> > > 	 dump_stack_lvl from register_lock_class+0x98c/0x99c
> > > 	 register_lock_class from __lock_acquire+0x74/0x293c
> > > 	 __lock_acquire from lock_acquire+0x134/0x398
> > > 	 lock_acquire from stmmac_get_stats64+0x2ac/0x2fc
> > > 	 stmmac_get_stats64 from dev_get_stats+0x44/0x130
> > > 	 dev_get_stats from rtnl_fill_stats+0x38/0x120
> > > 	 rtnl_fill_stats from rtnl_fill_ifinfo+0x834/0x17f4
> > > 	 rtnl_fill_ifinfo from rtmsg_ifinfo_build_skb+0xc0/0x144
> > > 	 rtmsg_ifinfo_build_skb from rtmsg_ifinfo+0x50/0x88
> > > 	 rtmsg_ifinfo from __dev_notify_flags+0xc0/0xec
> > > 	 __dev_notify_flags from dev_change_flags+0x50/0x5c
> > > 	 dev_change_flags from ip_auto_config+0x2f4/0x1260
> > > 	 ip_auto_config from do_one_initcall+0x70/0x35c
> > > 	 do_one_initcall from kernel_init_freeable+0x2ac/0x308
> > > 	 kernel_init_freeable from kernel_init+0x1c/0x138
> > > 	 kernel_init from ret_from_fork+0x14/0x2c
> > > 	Exception stack(0xe0815fb0 to 0xe0815ff8)
> > > 	5fa0:                                     00000000 00000000 00000000 00000000
> > > 	5fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
> > > 	5fe0: 00000000 00000000 00000000 00000000 00000013 00000000
> > > 	dwc2 49000000.usb-otg: new device is high-speed
> > > 
> > > I didn't try understand this problem, it's too close to quitting time
> > > :-)
> > 
> > Thanks for the bug report, I'm checking the code.
> 
> The newly added "struct u64_stats_sync syncp" uses a seqlock
> internally, which is broken into multiple words on 32bit machines, and
> needs to be initialized properly. You need to call u64_stats_init on
> syncp before first usage.

This is done. The problematic thing is that in stmmac_open() ->
__stmmac_open() the syncp initialized before is overwritten by

	memcpy(&priv->dma_conf, dma_conf, sizeof(*dma_conf));

Do I need to point out that this is ugly?

Together with Johannes Berg I debugged that in #netdev and we came up
with:

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 9a3182b9e767..a3481b48c77f 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -3893,7 +3893,7 @@ static int stmmac_open(struct net_device *dev)
 {
 	struct stmmac_priv *priv = netdev_priv(dev);
 	struct stmmac_dma_conf *dma_conf;
-	int ret;
+	int ret, i;
 
 	dma_conf = stmmac_setup_dma_desc(priv, dev->mtu);
 	if (IS_ERR(dma_conf))
@@ -3904,6 +3904,13 @@ static int stmmac_open(struct net_device *dev)
 		free_dma_desc_resources(priv, dma_conf);
 
 	kfree(dma_conf);
+
+	dma_conf = &priv->dma_conf;
+	for (i = 0; i < MTL_MAX_RX_QUEUES; i++)
+		u64_stats_init(&dma_conf->rx_queue[i].rxq_stats.syncp);
+	for (i = 0; i < MTL_MAX_TX_QUEUES; i++)
+		u64_stats_init(&dma_conf->tx_queue[i].txq_stats.syncp);
+
 	return ret;
 }
 
which works around the problem. Note however that the u64_stats_init()
calls must not be deleted from stmmac_dvr_probe() because it's used
there once before __stmmac_open() overwrites it.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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