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Message-ID: <b3d8a378-346d-4dd8-9af8-1529a4484184@leemhuis.info>
Date: Tue, 28 May 2024 07:22:31 +0200
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Subject: Re: [REGRESSION][BISECTED] wifi: RTL8821CE does not work in monitor
 mode
To: Christian Heusel <christian@heusel.eu>,
 Johannes Berg <johannes.berg@intel.com>, regressions@lists.linux.dev
Cc: Kalle Valo <kvalo@kernel.org>, linux-wireless@vger.kernel.org,
 Savyasaachi Vanga <savyasaachiv@gmail.com>
References: <chwoymvpzwtbmzryrlitpwmta5j6mtndocxsyqvdyikqu63lon@gfds653hkknl>
From: "Linux regression tracking (Thorsten Leemhuis)"
 <regressions@leemhuis.info>
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On 28.05.24 00:01, Christian Heusel wrote:
> 
> Savyasaachi reports that scanning for other stations in monitor mode
> does not work anymore with his RTL8821CE wireless network card for linux
> kernels after 6.8.9.

Thx for the report. A few remarks:

Please be more specific in cases like this, as "kernels after 6.8.9" can
mean "6.8.10+", "6.10-rc", or "6.9.y" (apparently it is the latter).
Yes, this is nitpicking, which is why I normally would not have said
anything -- but because you frequently report bugs it's likely in
everybody's interest to bring this up.

In a case like this it would also be good if the reporter could give
latest mainline a try, as (1) a fix might already be in there and (2)
some developers do not care at all about bugs in stable kernels (and
they are free to do so!). See
https://linux-regtracking.leemhuis.info/post/frequent-reasons-why-linux-kernel-bug-reports-are-ignored/
for details.

And sorry, there is something else: from the dmesg it looks a lot like
this report is from a patched vendor kernel that among others seems to
enable features like "forced interrupt request threading"
(https://github.com/zen-kernel/zen-kernel/wiki/Detailed-Feature-List ).
Such changes even if small and done carefully can lead to bugs like this
(yes, that particular feature I mentioned can be enabled through a
kernel parameter as well, but some developers would consider this to be
an unsupported configuration). The absolut minimum you should have done
is to mention that; but normally you never want to use such kernels for
reporting bugs upstream, as the problem might not be present in the
upstream code.

Ciao, Thorsten

> His workflow was putting the adapter in monitor mode by running
> "airmon-ng start wlan0" and then capture the surrounding stations with
> "airodump-ng wlan0".
> 
> We have bisected the issue together in the issue in the Arch Linux
> bugtracker[0] down to the following commit:
> 
>     0a44dfc070749 ("wifi: mac80211: simplify non-chanctx drivers")
> 
> Savyasaachi (in CC) offered to be available for questions and further
> debugging in this thread and some general debugging outputs are
> attached/below.
> 
> Reported-by: Savyasaachi Vanga <savyasaachiv@gmail.com>
> Bisected-by: Christian Heusel <christian@heusel.eu>
> 
> Cheers,
> Chris
> 
> [0]: https://gitlab.archlinux.org/archlinux/packaging/packages/linux/-/issues/54
> 
> ---
> 
> #regzbot link: https://gitlab.archlinux.org/archlinux/packaging/packages/linux/-/issues/54
> #regzbot introduced: 0a44dfc070749
> #regzbot title: wifi: RTL8821CE does not work in monitor mode
> 
> ---
> 
> lsusb:
> 
> Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
> Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
> Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
> Bus 003 Device 002: ID 0bda:c829 Realtek Semiconductor Corp. Bluetooth Radio
> Bus 003 Device 003: ID 0c45:6739 Microdia Integrated_Webcam_FHD
> Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
> 
> lspci:
> 
> 00:00.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Renoir/Cezanne Root Complex
> 00:00.2 IOMMU: Advanced Micro Devices, Inc. [AMD] Renoir/Cezanne IOMMU
> 00:01.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Renoir PCIe Dummy Host Bridge
> 00:01.2 PCI bridge: Advanced Micro Devices, Inc. [AMD] Renoir/Cezanne PCIe GPP Bridge
> 00:01.3 PCI bridge: Advanced Micro Devices, Inc. [AMD] Renoir/Cezanne PCIe GPP Bridge
> 00:02.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Renoir PCIe Dummy Host Bridge
> 00:02.1 PCI bridge: Advanced Micro Devices, Inc. [AMD] Renoir/Cezanne PCIe GPP Bridge
> 00:08.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Renoir PCIe Dummy Host Bridge
> 00:08.1 PCI bridge: Advanced Micro Devices, Inc. [AMD] Renoir Internal PCIe GPP Bridge to Bus
> 00:08.2 PCI bridge: Advanced Micro Devices, Inc. [AMD] Renoir Internal PCIe GPP Bridge to Bus
> 00:14.0 SMBus: Advanced Micro Devices, Inc. [AMD] FCH SMBus Controller (rev 51)
> 00:14.3 ISA bridge: Advanced Micro Devices, Inc. [AMD] FCH LPC Bridge (rev 51)
> 00:18.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Cezanne Data Fabric; Function 0
> 00:18.1 Host bridge: Advanced Micro Devices, Inc. [AMD] Cezanne Data Fabric; Function 1
> 00:18.2 Host bridge: Advanced Micro Devices, Inc. [AMD] Cezanne Data Fabric; Function 2
> 00:18.3 Host bridge: Advanced Micro Devices, Inc. [AMD] Cezanne Data Fabric; Function 3
> 00:18.4 Host bridge: Advanced Micro Devices, Inc. [AMD] Cezanne Data Fabric; Function 4
> 00:18.5 Host bridge: Advanced Micro Devices, Inc. [AMD] Cezanne Data Fabric; Function 5
> 00:18.6 Host bridge: Advanced Micro Devices, Inc. [AMD] Cezanne Data Fabric; Function 6
> 00:18.7 Host bridge: Advanced Micro Devices, Inc. [AMD] Cezanne Data Fabric; Function 7
> 01:00.0 Non-Volatile memory controller: Micron Technology Inc 2210 NVMe SSD [Cobain] (rev 03)
> 02:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8211/8411 PCI Express Gigabit Ethernet Controller (rev 15)
> 03:00.0 Network controller: Realtek Semiconductor Co., Ltd. RTL8821CE 802.11ac PCIe Wireless Network Adapter
> 04:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Barcelo (rev c2)
> 04:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Renoir Radeon High Definition Audio Controller
> 04:00.2 Encryption controller: Advanced Micro Devices, Inc. [AMD] Family 17h (Models 10h-1fh) Platform Security Processor
> 04:00.3 USB controller: Advanced Micro Devices, Inc. [AMD] Renoir/Cezanne USB 3.1
> 04:00.4 USB controller: Advanced Micro Devices, Inc. [AMD] Renoir/Cezanne USB 3.1
> 04:00.5 Multimedia controller: Advanced Micro Devices, Inc. [AMD] ACP/ACP3X/ACP6x Audio Coprocessor (rev 01)
> 04:00.6 Audio device: Advanced Micro Devices, Inc. [AMD] Family 17h/19h HD Audio Controller
> 05:00.0 SATA controller: Advanced Micro Devices, Inc. [AMD] FCH SATA Controller [AHCI mode] (rev 81)
> 05:00.1 SATA controller: Advanced Micro Devices, Inc. [AMD] FCH SATA Controller [AHCI mode] (rev 81)