linux-kernel - Hard lockup on Raspberry Pi 4 after v5.10-rc1

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Date:   Mon, 2 Nov 2020 00:29:00 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        linux-rpi-kernel@...ts.infradead.org
Cc:     bcm-kernel-feedback-list@...adcom.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Hard lockup on Raspberry Pi 4 after v5.10-rc1

Hi everyone,

Starting with v5.10-rc1, I appear to be experiencing hard lockups on my
Raspberry Pi 4 when compiling LLVM. My standard workflow for testing the
Raspberry Pi 4 has been compiling tip of tree LLVM (to catch host
AArch64 issues), compiling linux-next ARCH=arm64 defconfig, then booting
it with QEMU + KVM, which has caught a few issues so far. Starting with
v5.10-rc1, compiling LLVM causes the serial console to print junk like

 |▒pp▒p▒p▒p
 p|▒|▒|p▒p▒p|▒▒|▒|▒|p|▒▒|▒|▒|
 p▒pp▒▒▒|▒▒
 ▒
 ▒|▒|▒▒▒▒
 p▒
 ▒
 ▒▒
 ▒
 ▒p|p

then I lose my mosh connection and I see the lights on the front of the
Pi stop blinking.

I have managed to narrow it down to a commit somewhere in the armsoc DT
merge.

Good: 2e368dd2bbea ("Merge tag 'armsoc-drivers' of
git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc")
Bad: e533cda12d8f ("Merge tag 'armsoc-dt' of
git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc")

I have not been able to complete a full bisect due to a lack of time
unfortunately, I am sending this email to hopefully get some more eyes
on the issue.

$ head -n6 /boot/config.txt
# My settings
enable_uart=1
core_freq_min=500
kernel=Image
os_prefix=custom-mainline-gcc-arm64/
upstream_kernel=1

$ cat /boot/.firmware_revision
e8ddac7cd34b179efd702d4dc1efd0ccf44559b9

I can reproduce the issue with:

$ git clone --depth=1 https://github.com/llvm/llvm-project

$ mkdir -p llvm-project/build && cd llvm-project/build

$ cmake \
-G Ninja \
-DCMAKE_BUILD_TYPE=Release \
-DLLVM_ENABLE_PROJECTS="clang;lld" \
../llvm &&
ninja

If you need any more information or testing, please let me know!

Cheers,
Nathan