ath9 stopped transmitting multicast frames in Linux 5.14.0

ath9 stopped transmitting multicast frames in Linux 5.14.0

[Petr Pisar]

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Hello,

after upgrading Linux from 5.13.13 to 5.14.0 on my router with this wireless
device:

03:00.0 Network controller [0280]: Qualcomm Atheros AR93xx Wireless Network Adapter [168c:0030] (rev 01)
        Subsystem: Qualcomm Atheros AR93xx Wireless Network Adapter [168c:3116]
        Flags: bus master, fast devsel, latency 0, IRQ 18
        Memory at 81200000 (64-bit, non-prefetchable) [size=128K]
        Expansion ROM at 81220000 [disabled] [size=64K]
        Capabilities: [40] Power Management version 3
        Capabilities: [50] MSI: Enable- Count=1/4 Maskable+ 64bit+
        Capabilities: [70] Express Endpoint, MSI 00
        Capabilities: [100] Advanced Error Reporting
        Capabilities: [140] Virtual Channel
        Capabilities: [300] Device Serial Number 00-00-00-00-00-00-00-00
        Kernel driver in use: ath9k
        Kernel modules: ath9k

which works as a WiFi accesspoint, I noticed that WiFi clients cannot use IPv6
anymore. The problem is that the router cannot translate an IPv6 address of
the client to a MAC address. The reason is that IPv6 multicast packets used by
ICMPv6 neighbour discovery protocol do not reach the clients. In other words
the ath9k-driven device stopped transmitting multicast frames.

This can be reproduced with "ndisc6 -r 100 fe80::217:c4ff:fe4e:1552 wlan0"
command which queries (100 times) fe80::217:c4ff:fe4e:1552 address of
my client from the router. tcpdump on the ath9k device shows the queries,
but tcpdump on the client cannot see them.

The other way works correctly. I observed this with all two WiFi clients
I have (Pixel 3a phone, and a laptop with a Realtek chip). Upgrading to 5.14.1
did not help. Once I rebooted to 5.13.13, the functionality was restored.

Therefore I conclude this is regression in 5.14.0 Linux.

-- Petr

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Re: ath9 stopped transmitting multicast frames in Linux 5.14.0

[Petr Pisar]

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V Sat, Sep 04, 2021 at 08:20:57PM +0200, Petr Pisar napsal(a):
> Hello,
> 
> after upgrading Linux from 5.13.13 to 5.14.0 on my router with this wireless
> device:
> 
> 03:00.0 Network controller [0280]: Qualcomm Atheros AR93xx Wireless Network Adapter [168c:0030] (rev 01)
>         Subsystem: Qualcomm Atheros AR93xx Wireless Network Adapter [168c:3116]
>         Flags: bus master, fast devsel, latency 0, IRQ 18
>         Memory at 81200000 (64-bit, non-prefetchable) [size=128K]
>         Expansion ROM at 81220000 [disabled] [size=64K]
>         Capabilities: [40] Power Management version 3
>         Capabilities: [50] MSI: Enable- Count=1/4 Maskable+ 64bit+
>         Capabilities: [70] Express Endpoint, MSI 00
>         Capabilities: [100] Advanced Error Reporting
>         Capabilities: [140] Virtual Channel
>         Capabilities: [300] Device Serial Number 00-00-00-00-00-00-00-00
>         Kernel driver in use: ath9k
>         Kernel modules: ath9k
> 
> which works as a WiFi accesspoint, I noticed that WiFi clients cannot use IPv6
> anymore. The problem is that the router cannot translate an IPv6 address of
> the client to a MAC address. The reason is that IPv6 multicast packets used by
> ICMPv6 neighbour discovery protocol do not reach the clients. In other words
> the ath9k-driven device stopped transmitting multicast frames.
>
The same observation was reported here by Felix Fietkau in "[PATCH] Revert
"mac80211: do not use low data rates for data frames with no ack flag""
<https://marc.info/?l=linux-wireless&m=163091738109000&w=2> with a proposal to
revert the offending d333322361e7a099dc74df2498d3fa5fde5c4fa7 commit.

-- Petr

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Re: ath9 stopped transmitting multicast frames in Linux 5.14.0

[Kalle Valo]

Petr Pisar <petr.pisar@atlas.cz> writes:

> V Sat, Sep 04, 2021 at 08:20:57PM +0200, Petr Pisar napsal(a):
>> Hello,
>> 
>> after upgrading Linux from 5.13.13 to 5.14.0 on my router with this wireless
>> device:
>> 
>> 03:00.0 Network controller [0280]: Qualcomm Atheros AR93xx Wireless Network Adapter [168c:0030] (rev 01)
>>         Subsystem: Qualcomm Atheros AR93xx Wireless Network Adapter [168c:3116]
>>         Flags: bus master, fast devsel, latency 0, IRQ 18
>>         Memory at 81200000 (64-bit, non-prefetchable) [size=128K]
>>         Expansion ROM at 81220000 [disabled] [size=64K]
>>         Capabilities: [40] Power Management version 3
>>         Capabilities: [50] MSI: Enable- Count=1/4 Maskable+ 64bit+
>>         Capabilities: [70] Express Endpoint, MSI 00
>>         Capabilities: [100] Advanced Error Reporting
>>         Capabilities: [140] Virtual Channel
>>         Capabilities: [300] Device Serial Number 00-00-00-00-00-00-00-00
>>         Kernel driver in use: ath9k
>>         Kernel modules: ath9k
>> 
>> which works as a WiFi accesspoint, I noticed that WiFi clients cannot use IPv6
>> anymore. The problem is that the router cannot translate an IPv6 address of
>> the client to a MAC address. The reason is that IPv6 multicast packets used by
>> ICMPv6 neighbour discovery protocol do not reach the clients. In other words
>> the ath9k-driven device stopped transmitting multicast frames.
>
> The same observation was reported here by Felix Fietkau in "[PATCH] Revert
> "mac80211: do not use low data rates for data frames with no ack flag""
> <https://marc.info/?l=linux-wireless&m=163091738109000&w=2> with a proposal to
> revert the offending d333322361e7a099dc74df2498d3fa5fde5c4fa7 commit.

Very good, thanks for the followup.

-- 
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