Re: stmmac and XDP/ZC issue

Kurt Kanzenbach
2024-02-21T09:21:06Z

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On Wed Feb 21 2024, Kurt Kanzenbach wrote:
> On Tue Feb 20 2024, Stanislav Fomichev wrote:
>> On Tue, Feb 20, 2024 at 6:43 AM Maciej Fijalkowski
>> <maciej.fijalkowski@intel.com> wrote:
>>>
>>> On Tue, Feb 20, 2024 at 04:18:54PM +0300, Serge Semin wrote:
>>> > Hi Kurt
>>> >
>>> > On Tue, Feb 20, 2024 at 12:02:25PM +0100, Kurt Kanzenbach wrote:
>>> > > Hello netdev community,
>>> > >
>>> > > after updating to v6.8 kernel I've encountered an issue in the stmmac
>>> > > driver.
>>> > >
>>> > > I have an application which makes use of XDP zero-copy sockets. It works
>>> > > on v6.7. On v6.8 it results in the stack trace shown below. The program
>>> > > counter points to:
>>> > >
>>> > > - ./include/net/xdp_sock.h:192 and
>>> > > - ./drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:2681
>>> > >
>>> > > It seems to be caused by the XDP meta data patches. This one in
>>> > > particular 1347b419318d ("net: stmmac: Add Tx HWTS support to XDP ZC").
>>> > >
>>> > > To reproduce:
>>> > >
>>> > > - Hardware: imx93
>>> > > - Run ptp4l/phc2sys
>>> > > - Configure Qbv, Rx steering, NAPI threading
>>> > > - Run my application using XDP/ZC on queue 1
>>> > >
>>> > > Any idea what might be the issue here?
>>> > >
>>> > > Thanks,
>>> > > Kurt
>>> > >
>>> > > Stack trace:
>>> > >
>>> > > |[ 169.248150] imx-dwmac 428a0000.ethernet eth1: configured EST
>>> > > |[ 191.820913] imx-dwmac 428a0000.ethernet eth1: EST: SWOL has been switched
>>> > > |[ 226.039166] imx-dwmac 428a0000.ethernet eth1: entered promiscuous mode
>>> > > |[ 226.203262] imx-dwmac 428a0000.ethernet eth1: Register MEM_TYPE_PAGE_POOL RxQ-0
>>> > > |[ 226.203753] imx-dwmac 428a0000.ethernet eth1: Register MEM_TYPE_PAGE_POOL RxQ-1
>>> > > |[ 226.303337] imx-dwmac 428a0000.ethernet eth1: Register MEM_TYPE_XSK_BUFF_POOL RxQ-1
>>> > > |[ 255.822584] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
>>> > > |[ 255.822602] Mem abort info:
>>> > > |[ 255.822604] ESR = 0x0000000096000044
>>> > > |[ 255.822608] EC = 0x25: DABT (current EL), IL = 32 bits
>>> > > |[ 255.822613] SET = 0, FnV = 0
>>> > > |[ 255.822616] EA = 0, S1PTW = 0
>>> > > |[ 255.822618] FSC = 0x04: level 0 translation fault
>>> > > |[ 255.822622] Data abort info:
>>> > > |[ 255.822624] ISV = 0, ISS = 0x00000044, ISS2 = 0x00000000
>>> > > |[ 255.822627] CM = 0, WnR = 1, TnD = 0, TagAccess = 0
>>> > > |[ 255.822630] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
>>> > > |[ 255.822634] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000085fe1000
>>> > > |[ 255.822638] [0000000000000000] pgd=0000000000000000, p4d=0000000000000000
>>> > > |[ 255.822650] Internal error: Oops: 0000000096000044 [#1] PREEMPT_RT SMP
>>> > > |[ 255.822655] Modules linked in:
>>> > > |[ 255.822660] CPU: 0 PID: 751 Comm: napi/eth1-261 Not tainted 6.8.0-rc4-rt4-00100-g9c63d995ca19 #8
>>> > > |[ 255.822666] Hardware name: NXP i.MX93 11X11 EVK board (DT)
>>> > > |[ 255.822669] pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
>>> > > |[ 255.822674] pc : stmmac_tx_clean.constprop.0+0x848/0xc38
>>> > > |[ 255.822690] lr : stmmac_tx_clean.constprop.0+0x844/0xc38
>>> > > |[ 255.822696] sp : ffff800085ec3bc0
>>> > > |[ 255.822698] x29: ffff800085ec3bc0 x28: ffff000005b609e0 x27: 0000000000000001
>>> > > |[ 255.822706] x26: 0000000000000000 x25: ffff000005b60ae0 x24: 0000000000000001
>>> > > |[ 255.822712] x23: 0000000000000001 x22: ffff000005b649e0 x21: 0000000000000000
>>> > > |[ 255.822719] x20: 0000000000000020 x19: ffff800085291030 x18: 0000000000000000
>>> > > |[ 255.822725] x17: ffff7ffffc51c000 x16: ffff800080000000 x15: 0000000000000008
>>> > > |[ 255.822732] x14: ffff80008369b880 x13: 0000000000000000 x12: 0000000000008507
>>> > > |[ 255.822738] x11: 0000000000000040 x10: 0000000000000a70 x9 : ffff800080e32f84
>>> > > |[ 255.822745] x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000003ff0
>>> > > |[ 255.822751] x5 : 0000000000003c40 x4 : ffff000005b60000 x3 : 0000000000000000
>>> > > |[ 255.822757] x2 : 0000000000000000 x1 : 0000000000000000 x0 : 0000000000000000
>>> > > |[ 255.822764] Call trace:
>>> > > |[ 255.822766] stmmac_tx_clean.constprop.0+0x848/0xc38
>>>
>>> Shouldn't xsk_tx_metadata_complete() be called only when corresponding
>>> buf_type is STMMAC_TXBUF_T_XSK_TX?
>>
>> +1. I'm assuming Serge isn't enabling it explicitly, so none of the
>> metadata stuff should trigger in this case.
>
> The only other user of xsk_tx_metadata_complete() in mlx5 guards it with
> xp_tx_metadata_enabled(). Seems like that's missing in stmmac?

Well, the following patch seems to help:

commit e85ab4b97b4d6e50036435ac9851b876c221f580
Author: Kurt Kanzenbach <kurt@linutronix.de>
Date: Wed Feb 21 08:18:15 2024 +0100

net: stmmac: Complete meta data only when enabled

Currently using XDP sockets on stmmac results in a kernel crash:

|[ 255.822584] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
|[...]
|[ 255.822764] Call trace:
|[ 255.822766] stmmac_tx_clean.constprop.0+0x848/0xc38

The program counter indicates xsk_tx_metadata_complete(). However, this
function shouldn't be called unless metadata is actually enabled.

Tested on imx93.

Fixes: 1347b419318d ("net: stmmac: Add Tx HWTS support to XDP ZC")
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 9df27f03a8cb..77c62b26342d 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -2678,9 +2678,10 @@ static int stmmac_tx_clean(struct stmmac_priv *priv, int budget, u32 queue,
.desc = p,
};

- xsk_tx_metadata_complete(&tx_q->tx_skbuff_dma[entry].xsk_meta,
- &stmmac_xsk_tx_metadata_ops,
- &tx_compl);
+ if (xp_tx_metadata_enabled(tx_q->xsk_pool))
+ xsk_tx_metadata_complete(&tx_q->tx_skbuff_dma[entry].xsk_meta,
+ &stmmac_xsk_tx_metadata_ops,
+ &tx_compl);
}
}

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