Re: [REGRESSION] Power9 pseries boot hang in v7.2-rc6, narrowed to PowerPC GENERIC_ENTRY conversion window

Hi Venkat.

On 8/4/26 2:04 PM, Venkat Rao Bagalkote wrote:

Hi,

I'm seeing a boot regression on a Power9 pseries LPAR. The system hangs 
very early during boot after:

Quiescing Open Firmware ...
Booting Linux via __start() ...

That is strange. not sure where to look at without any logs.
Is it a specific config that fails or this specific LPAR that fails?

No further kernel output is produced.

Known good:8cd9520d35a6 ("Linux 7.1")
Known bad: 075b74841bd0 ("Linux 7.2-rc6")

Is the kernel built correct at 075b74841bd0 without any errors?

Initial bisect:

A full bisect from v7.1 to v7.2-rc6 converged to:

c5e8e224eb7a
MIPS: RB532: attach the software node to its target GPIO controller


However this commit only modifies:

arch/mips/rb532/devices.c
arch/mips/rb532/gpio.c

and appears unrelated to a Power9/pseries boot hang.

I then narrowed the investigation to the PowerPC pull.

The following commits were tested and boot successfully:

baa590018fbf powerpc: rename arch_irq_disabled_regs
dec63ea6faff powerpc: Prepare to build with generic entry/exit framework
09a9d3a8499d powerpc: introduce arch_enter_from_user_mode
893082ac769b powerpc: Prepare for IRQ entry exit

The following commit reproduces the hang:

334f3f6d7a16 powerpc/entry: Disable interrupts before irqentry_exit



Between the last known good and first known bad points:


893082ac769b powerpc: Prepare for IRQ entry exit
...
bee25f97ad24 powerpc: Enable GENERIC_ENTRY feature
...
334f3f6d7a16 powerpc/entry: Disable interrupts before irqentry_exit


The only substantial architectural/runtime change in this window appears 
to be:

bee25f97ad24 powerpc: Enable GENERIC_ENTRY feature



I attempted to test:

bee25f97ad24 powerpc: Enable GENERIC_ENTRY feature

directly, however that commit does not build with my configuration due to:

arch/powerpc/kernel/ptrace/ptrace.c

error: implicit declaration of function 'trace_sys_enter'
error: implicit declaration of function 'trace_sys_exit'

Therefore I could not directly classify bee25f97ad24 as good or bad.

Can you try one commit after this and see if it builds?
i.e  "powerpc: Remove unused functions"

Please let me know if there are specific debug patches or boot 
parameters you'd like me to test.


Attached is the config file I used.


Regards,

Venkat.