Re: [PATCH net-next v3] virtio_net: add support for Byte Queue Limits

[Jiri Pirko <jiri@resnulli.us>]

Mon, Aug 12, 2024 at 06:55:26PM CEST, m.szyprowski@samsung.com wrote:
>On 12.08.2024 18:47, Jiri Pirko wrote:
>> Mon, Aug 12, 2024 at 04:57:24PM CEST, m.szyprowski@samsung.com wrote:
>>> On 18.06.2024 16:44, Jiri Pirko wrote:
>>>> From: Jiri Pirko <jiri@nvidia.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@nvidia.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@target:~# 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.
>> Will fix this tomorrow. In the meantime, could you provide full
>> reproduce steps?
>
>Well, it is easy to reproduce it simply by calling
>
># time rtcwake -s10 -mmem
>
>a few times and sooner or later it will cause a kernel panic.

I found the problem. Following patch will help:


diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 3f10c72743e9..c6af18948092 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2867,8 +2867,8 @@ static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
 	if (err < 0)
 		goto err_xdp_reg_mem_model;
 
-	virtnet_napi_enable(vi->rq[qp_index].vq, &vi->rq[qp_index].napi);
 	netdev_tx_reset_queue(netdev_get_tx_queue(vi->dev, qp_index));
+	virtnet_napi_enable(vi->rq[qp_index].vq, &vi->rq[qp_index].napi);
 	virtnet_napi_tx_enable(vi, vi->sq[qp_index].vq, &vi->sq[qp_index].napi);
 
 	return 0;


Will submit the patch in a jiff. Thanks!



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