Re: [PATCH net-next v5 7/7] xsk: use generic DMA sync shortcut instead of a custom one

[Alexander Lobakin]

From: Jakub Kicinski <kuba@xxxxxxxxxx>
Date: Mon, 6 May 2024 11:29:31 -0700

> On Mon,  6 May 2024 11:48:55 +0200 Alexander Lobakin wrote:
>> XSk infra's been using its own DMA sync shortcut to try avoiding
>> redundant function calls. Now that there is a generic one, remove
>> the custom implementation and rely on the generic helpers.
>> xsk_buff_dma_sync_for_cpu() doesn't need the second argument anymore,
>> remove it.
> 
> I think this is crashing xsk tests:
> 
>   [   91.048963] BUG: kernel NULL pointer dereference, address: 0000000000000464
>   [   91.049412] #PF: supervisor read access in kernel mode
>   [   91.049739] #PF: error_code(0x0000) - not-present page
>   [   91.050057] PGD 0 P4D 0
>   [   91.050221] Oops: 0000 [#1] PREEMPT SMP NOPTI
>   [   91.050500] CPU: 1 PID: 114 Comm: new_name Tainted: G           OE      6.9.0-rc6-gad3c108348fd-dirty #372
>   [   91.051088] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
>   [   91.051649] RIP: 0010:xp_alloc+0x76/0x240

Ah okay. Didn't account generic (non-ZC) XSk. Will fix in v6.
Thanks for the report!

>   [   91.051903] Code: 48 89 0a 48 89 00 48 89 40 08 41 c7 44 24 34 00 00 00 00 49 8b 44 24 18 48 05 00 01 00 00 49 89 04 24 49 89 44 24 10 48 8b 3b <f6> 87 64 04 00 00 20 0f 85 16 01 00 00 48 8b 44 24 08 65 48 33 04
>   [   91.053055] RSP: 0018:ffff99e7c00f0b00 EFLAGS: 00010286
>   [   91.053400] RAX: ffff99e7c0c9d100 RBX: ffff89a400901c00 RCX: 0000000000010000
>   [   91.053838] RDX: 0000000000000000 RSI: 0000000000000010 RDI: 0000000000000000
>   [   91.054277] RBP: ffff89a4026e30e0 R08: 0000000000000001 R09: 0000000000009000
>   [   91.054716] R10: 779660ad50f0d4e6 R11: 79b5ce88640fb4f7 R12: ffff89a40c31d870
>   [   91.055156] R13: 0000000000000020 R14: 0000000000000000 R15: ffff89a4068c6000
>   [   91.055596] FS:  00007f87685bef80(0000) GS:ffff89a43bd00000(0000) knlGS:0000000000000000
>   [   91.056090] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   [   91.056458] CR2: 0000000000000464 CR3: 000000010229c001 CR4: 0000000000770ef0
>   [   91.056904] PKRU: 55555554
>   [   91.057079] Call Trace:
>   [   91.057237]  <IRQ>
>   [   91.057371]  ? __die_body+0x1f/0x70
>   [   91.057595]  ? page_fault_oops+0x15a/0x460
>   [   91.057852]  ? find_held_lock+0x2b/0x80
>   [   91.058093]  ? __skb_flow_dissect+0x30f/0x1f10
>   [   91.058374]  ? lock_release+0xbd/0x280
>   [   91.058610]  ? exc_page_fault+0x67/0x1e0
>   [   91.058859]  ? asm_exc_page_fault+0x26/0x30
>   [   91.059126]  ? xp_alloc+0x76/0x240
>   [   91.059341]  __xsk_rcv+0x1f0/0x360
>   [   91.059558]  ? __skb_get_hash+0x5b/0x1f0
>   [   91.059804]  ? __skb_get_hash+0x5b/0x1f0
>   [   91.060050]  __xsk_map_redirect+0x7c/0x2c0
>   [   91.060315]  ? rcu_read_lock_held_common+0x2e/0x50
>   [   91.060622]  xdp_do_redirect+0x28f/0x4b0
>   [   91.060871]  veth_xdp_rcv_skb+0x29e/0x930
>   [   91.061126]  veth_xdp_rcv+0x184/0x290
>   [   91.061358]  ? update_load_avg+0x8c/0x8c0
>   [   91.061609]  ? select_task_rq_fair+0x1ff/0x15a0
>   [   91.061894]  ? place_entity+0x19/0x100
>   [   91.062131]  veth_poll+0x6c/0x2f0
>   [   91.062343]  ? _raw_spin_unlock_irqrestore+0x27/0x50
>   [   91.062653]  ? try_to_wake_up+0x261/0x8d0
>   [   91.062905]  ? find_held_lock+0x2b/0x80
>   [   91.063147]  __napi_poll+0x27/0x200
>   [   91.063376]  net_rx_action+0x172/0x320
>   [   91.063617]  __do_softirq+0xb6/0x3a3
>   [   91.063843]  ? __dev_direct_xmit+0x167/0x1b0
>   [   91.064114]  do_softirq.part.0+0x3b/0x70
>   [   91.064373]  </IRQ>
>   [   91.064511]  <TASK>
>   [   91.064650]  __local_bh_enable_ip+0xbd/0xe0
>   [   91.064913]  __dev_direct_xmit+0x16c/0x1b0
>   [   91.065171]  xsk_generic_xmit+0x703/0xb10
>   [   91.065425]  xsk_sendmsg+0x21f/0x2f0

Olek