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Subject: Re: [PATCH v8 6/6] mt76: mt76x02: add channel switch support for usb
 interfaces
To:     Stanislaw Gruszka <sgruszka@redhat.com>
Cc:     nbd@nbd.name, linux-wireless@vger.kernel.org,
        lorenzo.bianconi@redhat.com
References: <20191121180001.22451-1-markus.theil@tu-ilmenau.de>
 <20191121180001.22451-7-markus.theil@tu-ilmenau.de>
 <20191125130449.GC28102@redhat.com>
 <76778e31-5757-6e8b-eecb-b1b3a23acc6d@tu-ilmenau.de>
 <7de34f93-ab33-400b-6b5b-d126bab43b97@tu-ilmenau.de>
 <20191125170252.GC14273@redhat.com>
From:   Markus Theil <markus.theil@tu-ilmenau.de>
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Message-ID: <fe66eba9-8520-a4fc-6b93-189aac82c927@tu-ilmenau.de>
Date:   Mon, 25 Nov 2019 19:30:11 +0100
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On 11/25/19 6:02 PM, Stanislaw Gruszka wrote:
> On Mon, Nov 25, 2019 at 04:32:42PM +0100, Markus Theil wrote:
>> On 11/25/19 3:51 PM, Markus Theil wrote:
>>> On 11/25/19 2:04 PM, Stanislaw Gruszka wrote:
>>>> On Thu, Nov 21, 2019 at 07:00:01PM +0100, Markus Theil wrote:
>>>>> diff --git a/drivers/net/wireless/mediatek/mt76/mt76x02_usb_core.c b/drivers/net/wireless/mediatek/mt76/mt76x02_usb_core.c
>>>>> index 90c024f12302..b9bd6bfb2a9d 100644
>>>>> --- a/drivers/net/wireless/mediatek/mt76/mt76x02_usb_core.c
>>>>> +++ b/drivers/net/wireless/mediatek/mt76/mt76x02_usb_core.c
>>>>> @@ -210,6 +210,12 @@ static void mt76x02u_pre_tbtt_work(struct work_struct *work)
>>>>>  
>>>>>  	mt76x02_mac_set_beacon_prepare(dev);
>>>>>  
>>>>> +	mt76_csa_check(&dev->mt76);
>>>>> +	if (dev->mt76.csa_complete) {
>>>>> +		mt76_csa_finish(&dev->mt76);
>>>>> +		goto out;
>>>>> +	}
>>>> mmio counterpart setup beacons on CSA, but do not sent buffered
>>>> PS frames. Perhaps here we should do the same. However not sending
>>>> beacons on one TBTT looks ok to me as well.
>>>>
>>>> Stanislaw
>>>>
>>> If I change the order of beacon iteration and csa check, the following warning in mac80211 gets triggered:
>>>
>>> 	/* the counter should never reach 0 */
>>> 	WARN_ON_ONCE(!beacon->csa_current_counter);
>>>
>>> Dmesg output looks like this:
>>>
>>> [  153.829617] ------------[ cut here ]------------
>>> [  153.829752] WARNING: CPU: 0 PID: 224 at net/mac80211/tx.c:4318 __ieee80211_csa_update_counter.isra.0.part.0+0x5/0x10 [mac80211]
>>> [  153.829756] Modules linked in: ccm bridge stp llc nft_masq nft_chain_nat nf_nat nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 libcrc32c nf_tables_set nf_tables nfnetlink ath10k_pci amd64_edac_mod mt76x2u edac_mce_amd mt76x2_common ath10k_core mt76x02_usb kvm_amd mt76_usb mt76x02_lib mt76 kvm ath mac80211 irqbypass crct10dif_pclmul crc32_pclmul ghash_clmulni_intel cfg80211 pcengines_apuv2 gpio_keys_polled aesni_intel input_polldev crypto_simd gpio_amd_fch cryptd glue_helper igb pcspkr k10temp fam15h_power rfkill sp5100_tco i2c_piix4 libarc4 ccp i2c_algo_bit dca rng_core uio_pdrv_genirq uio leds_gpio evdev mac_hid pinctrl_amd coreboot_table acpi_cpufreq ip_tables x_tables ext4 crc32c_generic crc16 mbcache jbd2 sd_mod ahci sdhci_pci libahci cqhci libata sdhci crc32c_intel xhci_pci ehci_pci mmc_core xhci_hcd scsi_mod ehci_hcd gpio_keys
>>> [  153.829948] CPU: 0 PID: 224 Comm: kworker/0:1H Not tainted 5.4.0-rc7-1-01110-g19b7e21c55c8 #32
>>> [  153.829952] Hardware name: PC Engines apu2/apu2, BIOS v4.10.0.3 11/07/2019
>>> [  153.829966] Workqueue: events_highpri mt76x02u_pre_tbtt_work [mt76x02_usb]
>>> [  153.830067] RIP: 0010:__ieee80211_csa_update_counter.isra.0.part.0+0x5/0x10 [mac80211]
>>> [  153.830077] Code: 4c 89 4a 18 c3 48 8b 47 10 4c 89 4f 10 48 89 4e 18 48 89 46 20 4c 89 08 eb a1 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 <0f> 0b c3 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 54 53 48 89 fb
>>> [  153.830082] RSP: 0018:ffffbde8803d7c80 EFLAGS: 00010246
>>> [  153.830089] RAX: 0000000000000003 RBX: ffffbde8803d7d20 RCX: ffffa3b01df8f658
>>> [  153.830093] RDX: ffffbde8803d7d20 RSI: ffffa3b02901d450 RDI: ffffbde8803d7ce0
>>> [  153.830097] RBP: ffffa3b0267007a0 R08: ffffffff8d011040 R09: 0000000000000000
>>> [  153.830101] R10: ffffa3b029908098 R11: ffffa3b02ab2ab38 R12: 0000000000000000
>>> [  153.830105] R13: ffffa3b02901d450 R14: 0000000000000000 R15: ffffa3b0284eae00
>>> [  153.830111] FS:  0000000000000000(0000) GS:ffffa3b02aa00000(0000) knlGS:0000000000000000
>>> [  153.830115] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> [  153.830119] CR2: 00007fbb6b5c9f30 CR3: 0000000126ee2000 CR4: 00000000000406f0
>>> [  153.830124] Call Trace:
>>> [  153.830203]  __ieee80211_beacon_get+0x4c2/0x4d0 [mac80211]
>>> [  153.830312]  ieee80211_beacon_get_tim+0x41/0x150 [mac80211]
>>> [  153.830336]  mt76x02_update_beacon_iter+0x2d/0x40 [mt76x02_lib]
>>> [  153.830352]  ? mt76x02_add_buffered_bc+0x80/0x80 [mt76x02_lib]
>>> [  153.830420]  __iterate_interfaces+0x74/0x110 [mac80211]
>>> [  153.830469]  ? mt76x02_add_buffered_bc+0x80/0x80 [mt76x02_lib]
>>> [  153.830566]  ieee80211_iterate_interfaces+0x3a/0x50 [mac80211]
>>> [  153.830580]  mt76x02u_pre_tbtt_work+0x96/0x220 [mt76x02_usb]
>>> [  153.830600]  process_one_work+0x1e2/0x3b0
>>> [  153.830610]  worker_thread+0x4a/0x3d0
>>> [  153.830623]  kthread+0xfb/0x130
>>> [  153.830631]  ? process_one_work+0x3b0/0x3b0
>>> [  153.830639]  ? kthread_park+0x90/0x90
>>> [  153.830650]  ret_from_fork+0x22/0x40
>>> [  153.830665] ---[ end trace 7a658e5cbfd0f9d1 ]---
>>>
>>> Markus
>>>
>> In my current local changes I've decoupled checking csa_check and mt76_csa_finish, like it is in the mmio case. As usb has no tbtt interrupt,
>> I just schedule a delayed work around the estimated beacon transmission time and finish csa there. I'll send another series, if this works.
> I would prefer not to add yet another delayed work. Does the warning
> still happen if you arrange code like this?
>
>         mt76x02_mac_set_beacon_prepare(dev);
>
>         ieee80211_iterate_active_interfaces(mt76_hw(dev),
>                 IEEE80211_IFACE_ITER_RESUME_ALL,
>                 mt76x02_update_beacon_iter, dev);
>
>         mt76_csa_check(&dev->mt76);
>         if (dev->mt76.csa_complete) {
>                 mt76_csa_finish(&dev->mt76);
>                 goto out;
>         }
>
>         nbeacons = hweight8(dev->mt76.beacon_mask);
>         mt76x02_enqueue_buffered_bc(dev, &data, N_BCN_SLOTS - nbeacons);
> 	...
> out:
>         mt76x02_mac_set_beacon_finish(dev);
>         mt76x02u_restart_pre_tbtt_timer(dev);
>
>
You're code works, if I add some locking. ieee80211_iterate_active_interfaces -> ieee80211_iterate_active_interfaces_atomic did the trick for me. Otherwise I get the dmesg output from above.
After using ieee80211_iterate_active_interfaces_atomic I got the following dmesg output after/while a channel switch:

[   63.115806] divide error: 0000 [#1] PREEMPT SMP NOPTI
[   63.121054] CPU: 0 PID: 225 Comm: kworker/u8:2 Tainted: G        W         5.4.0-rc7-1-01110-g19b7e21c55c8 #39
[   63.131331] Hardware name: PC Engines apu2/apu2, BIOS v4.10.0.3 11/07/2019
[   63.138399] Workqueue: mt76u mt76u_tx_status_data [mt76_usb]
[   63.144258] RIP: 0010:mt76_calc_rx_airtime+0x12b/0x150 [mt76]
[   63.150281] Code: 8d 34 76 48 8d 34 b1 0f b6 4e 07 66 85 c9 74 25 66 83 f9 01 75 1c b9 24 00 00 00 89 d0 0f b7 76 04 c1 e0 05 8d 04 d0 01 c0 99 <f7> fe 01 c8 c3 31 c0 c3 0f 0b c3 44 89 c8 83 e0 01 3c 01 19 c9 83
[   63.169699] RSP: 0018:ffffbd694032fcf0 EFLAGS: 00010216
[   63.175176] RAX: 0000000000002850 RBX: 0000000000000001 RCX: 00000000000000ca
[   63.182535] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffa20068253538
[   63.189983] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[   63.197381] R10: 0000000000000000 R11: ffffbd694032fcb0 R12: ffffbd694032fdb0
[   63.204782] R13: 0000000000000000 R14: ffffbd694032fd00 R15: ffffa20068251e40
[   63.212228] FS:  0000000000000000(0000) GS:ffffa2006aa00000(0000) knlGS:0000000000000000
[   63.220614] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   63.226500] CR2: 00007fe65ba85cb0 CR3: 00000001293b6000 CR4: 00000000000406f0
[   63.233841] Call Trace:
[   63.236410]  mt76_calc_tx_airtime+0xf4/0x190 [mt76]
[   63.241464]  mt76x02_send_tx_status+0x1cd/0x3f0 [mt76x02_lib]
[   63.247430]  mt76x02_tx_status_data+0x54/0x80 [mt76x02_lib]
[   63.253186]  mt76u_tx_status_data+0x63/0xc0 [mt76_usb]
[   63.258451]  process_one_work+0x1e2/0x3b0
[   63.262533]  worker_thread+0x4a/0x3d0
[   63.266306]  kthread+0xfb/0x130
[   63.269550]  ? process_one_work+0x3b0/0x3b0
[   63.273893]  ? kthread_park+0x90/0x90
[   63.277677]  ret_from_fork+0x22/0x40
[   63.281411] Modules linked in: ccm bridge stp llc mt76x2u mt76x2_common mt76x02_usb mt76_usb mt76x02_lib mt76 nft_masq nft_chain_nat nf_nat nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 libcrc32c nf_tables_set nf_tables nfnetlink ath10k_pci ath10k_core amd64_edac_mod edac_mce_amd ath kvm_amd mac80211 kvm irqbypass crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel pcengines_apuv2 cfg80211 gpio_keys_polled crypto_simd input_polldev gpio_amd_fch cryptd igb glue_helper pcspkr fam15h_power sp5100_tco k10temp i2c_piix4 rfkill i2c_algo_bit ccp libarc4 dca rng_core uio_pdrv_genirq evdev leds_gpio uio mac_hid coreboot_table acpi_cpufreq pinctrl_amd sr_mod cdrom ip_tables x_tables ext4 crc32c_generic crc16 mbcache jbd2 sd_mod usb_storage ahci libahci libata xhci_pci sdhci_pci xhci_hcd scsi_mod cqhci sdhci ehci_pci crc32c_intel ehci_hcd mmc_core gpio_keys
[   63.365937] ---[ end trace f13e9cdc5f55db9e ]---
[   63.370802] RIP: 0010:mt76_calc_rx_airtime+0x12b/0x150 [mt76]
[   63.376807] Code: 8d 34 76 48 8d 34 b1 0f b6 4e 07 66 85 c9 74 25 66 83 f9 01 75 1c b9 24 00 00 00 89 d0 0f b7 76 04 c1 e0 05 8d 04 d0 01 c0 99 <f7> fe 01 c8 c3 31 c0 c3 0f 0b c3 44 89 c8 83 e0 01 3c 01 19 c9 83
[   63.396220] RSP: 0018:ffffbd694032fcf0 EFLAGS: 00010216
[   63.401660] RAX: 0000000000002850 RBX: 0000000000000001 RCX: 00000000000000ca
[   63.409145] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffa20068253538
[   63.416505] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
[   63.423988] R10: 0000000000000000 R11: ffffbd694032fcb0 R12: ffffbd694032fdb0
[   63.431425] R13: 0000000000000000 R14: ffffbd694032fd00 R15: ffffa20068251e40
[   63.438793] FS:  0000000000000000(0000) GS:ffffa2006aa00000(0000) knlGS:0000000000000000
[   63.447141] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   63.453216] CR2: 00007fe65ba85cb0 CR3: 00000001293b6000 CR4: 00000000000406f0

I would guess, that 
	mt76_calc_legacy_rate_duration: duration += (len * 10) / rate->bitrate;
triggers this kind of message.