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

[Shrikanth Hegde <sshegde@linux.ibm.com>]

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.