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

[Venkat Rao Bagalkote]

Hi Shrikanth,


On 04/08/26 8:23 pm, Shrikanth Hegde wrote:
> 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?

The known bad revision 075b74841bd0 ("Linux 7.2-rc6") builds 
successfully with my configuration and the issue is observed at boot 
time only.

> > 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"
I tested:

6ed60999d33d ("powerpc: Remove unused functions")

The kernel builds successfully with my configuration, but the system 
still hangs during boot on the Power9 pseries LPAR after:

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

with no further output.

So currently I have:

  893082ac769b ("powerpc: Prepare for IRQ entry exit")  GOOD
  bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature") UNTESTABLE
  6ed60999d33d ("powerpc: Remove unused functions")      BAD

Given that 6ed60999d33d builds and reproduces the hang, the regression 
appears to be present immediately after the introduction of GENERIC_ENTRY.


Regards,

Venkat.

> > 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.