Message-ID: <cabe5701-6e25-4a15-b711-924034044331@samsung.com>
Date: Mon, 12 Aug 2024 16:57:24 +0200
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, mst@...hat.com, jasowang@...hat.com,
	xuanzhuo@...ux.alibaba.com, virtualization@...ts.linux.dev, ast@...nel.org,
	daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
	dave.taht@...il.com, kerneljasonxing@...il.com, hengqi@...ux.alibaba.com
Subject: Re: [PATCH net-next v3] virtio_net: add support for Byte Queue
 Limits

Hi,

On 18.06.2024 16:44, Jiri Pirko wrote:
> From: Jiri Pirko <jiri@...dia.com>
>
> Add support for Byte Queue Limits (BQL).
>
> Tested on qemu emulated virtio_net device with 1, 2 and 4 queues.
> Tested with fq_codel and pfifo_fast. Super netperf with 50 threads is
> running in background. Netperf TCP_RR results:
>
> NOBQL FQC 1q:  159.56  159.33  158.50  154.31    agv: 157.925
> NOBQL FQC 2q:  184.64  184.96  174.73  174.15    agv: 179.62
> NOBQL FQC 4q:  994.46  441.96  416.50  499.56    agv: 588.12
> NOBQL PFF 1q:  148.68  148.92  145.95  149.48    agv: 148.2575
> NOBQL PFF 2q:  171.86  171.20  170.42  169.42    agv: 170.725
> NOBQL PFF 4q: 1505.23 1137.23 2488.70 3507.99    agv: 2159.7875
>    BQL FQC 1q: 1332.80 1297.97 1351.41 1147.57    agv: 1282.4375
>    BQL FQC 2q:  768.30  817.72  864.43  974.40    agv: 856.2125
>    BQL FQC 4q:  945.66  942.68  878.51  822.82    agv: 897.4175
>    BQL PFF 1q:  149.69  151.49  149.40  147.47    agv: 149.5125
>    BQL PFF 2q: 2059.32  798.74 1844.12  381.80    agv: 1270.995
>    BQL PFF 4q: 1871.98 4420.02 4916.59 13268.16   agv: 6119.1875
>
> Signed-off-by: Jiri Pirko <jiri@...dia.com>
> ---
> v2->v3:
> - fixed the switch from/to orphan mode while skbs are yet to be
>    completed by using the second least significant bit in virtqueue
>    token pointer to indicate skb is orphan. Don't account orphan
>    skbs in completion.
> - reorganized parallel skb/xdp free stats accounting to napi/others.
> - fixed kick condition check in orphan mode
> v1->v2:
> - moved netdev_tx_completed_queue() call into __free_old_xmit(),
>    propagate use_napi flag to __free_old_xmit() and only call
>    netdev_tx_completed_queue() in case it is true
> - added forgotten call to netdev_tx_reset_queue()
> - fixed stats for xdp packets
> - fixed bql accounting when __free_old_xmit() is called from xdp path
> - handle the !use_napi case in start_xmit() kick section
> ---
>   drivers/net/virtio_net.c | 81 ++++++++++++++++++++++++++++------------
>   1 file changed, 57 insertions(+), 24 deletions(-)

I've recently found an issue with virtio-net driver and system 
suspend/resume. Bisecting pointed to the c8bd1f7f3e61 ("virtio_net: add 
support for Byte Queue Limits") commit and this patch. Once it got 
merged to linux-next and then Linus trees, the driver occasionally 
crashes with the following log (captured on QEMU's ARM 32bit 'virt' 
machine):

root@...get:~# time rtcwake -s10 -mmem
rtcwake: wakeup from "mem" using /dev/rtc0 at Sat Aug 10 12:40:26 2024
PM: suspend entry (s2idle)
Filesystems sync: 0.000 seconds
Freezing user space processes
Freezing user space processes completed (elapsed 0.006 seconds)
OOM killer disabled.
Freezing remaining freezable tasks
Freezing remaining freezable tasks completed (elapsed 0.001 seconds)
------------[ cut here ]------------
kernel BUG at lib/dynamic_queue_limits.c:99!
Internal error: Oops - BUG: 0 [#1] SMP ARM
Modules linked in: bluetooth ecdh_generic ecc libaes
CPU: 1 PID: 1282 Comm: rtcwake Not tainted 
6.10.0-rc3-00732-gc8bd1f7f3e61 #15240
Hardware name: Generic DT based system
PC is at dql_completed+0x270/0x2cc
LR is at __free_old_xmit+0x120/0x198
pc : [<c07ffa54>]    lr : [<c0c42bf4>]    psr: 80000013
...
Flags: Nzcv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 10c5387d  Table: 43a4406a  DAC: 00000051
...
Process rtcwake (pid: 1282, stack limit = 0xfbc21278)
Stack: (0xe0805e80 to 0xe0806000)
...
Call trace:
  dql_completed from __free_old_xmit+0x120/0x198
  __free_old_xmit from free_old_xmit+0x44/0xe4
  free_old_xmit from virtnet_poll_tx+0x88/0x1b4
  virtnet_poll_tx from __napi_poll+0x2c/0x1d4
  __napi_poll from net_rx_action+0x140/0x2b4
  net_rx_action from handle_softirqs+0x11c/0x350
  handle_softirqs from call_with_stack+0x18/0x20
  call_with_stack from do_softirq+0x48/0x50
  do_softirq from __local_bh_enable_ip+0xa0/0xa4
  __local_bh_enable_ip from virtnet_open+0xd4/0x21c
  virtnet_open from virtnet_restore+0x94/0x120
  virtnet_restore from virtio_device_restore+0x110/0x1f4
  virtio_device_restore from dpm_run_callback+0x3c/0x100
  dpm_run_callback from device_resume+0x12c/0x2a8
  device_resume from dpm_resume+0x12c/0x1e0
  dpm_resume from dpm_resume_end+0xc/0x18
  dpm_resume_end from suspend_devices_and_enter+0x1f0/0x72c
  suspend_devices_and_enter from pm_suspend+0x270/0x2a0
  pm_suspend from state_store+0x68/0xc8
  state_store from kernfs_fop_write_iter+0x10c/0x1cc
  kernfs_fop_write_iter from vfs_write+0x2b0/0x3dc
  vfs_write from ksys_write+0x5c/0xd4
  ksys_write from ret_fast_syscall+0x0/0x54
Exception stack(0xe8bf1fa8 to 0xe8bf1ff0)
...
---[ end trace 0000000000000000 ]---
Kernel panic - not syncing: Fatal exception in interrupt
---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---

I have fully reproducible setup for this issue. Reverting it together 
with f8321fa75102 ("virtio_net: Fix napi_skb_cache_put warning") (due to 
some code dependencies) fixes this issue on top of Linux v6.11-rc1 and 
recent linux-next releases. Let me know if I can help debugging this 
issue further and help fixing.

 > ...

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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