Re: [PATCH v3 3/6] powerpc/kexec: Disable ftrace before switching to the new kernel

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

Michael Ellerman wrote:
> Michael Ellerman <mpe@ellerman.id.au> writes:
>=20
>> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> writes:
>>> If function_graph tracer is enabled during kexec, we see the below
>>> exception in the simulator:
>>> 	root@(none):/# kexec -e
>>> 	kvm: exiting hardware virtualization
>>> 	kexec_core: Starting new kernel
>>> 	[   19.262020070,5] OPAL: Switch to big-endian OS
>>> 	kexec: Starting switchover sequence.
>>> 	Interrupt to 0xC000000000004380 from 0xC000000000004380
>>> 	** Execution stopped: Continuous Interrupt, Instruction caused excepti=
on,  **
>>>
>>> Now that we have a more effective way to disable ftrace, let's use that
>>> before switching to a new kernel during kexec.
>>>
>>> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
>>> ---
>>>  arch/powerpc/kernel/machine_kexec.c | 6 ++----
>>>  1 file changed, 2 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/arch/powerpc/kernel/machine_kexec.c b/arch/powerpc/kernel/=
machine_kexec.c
>>> index 2694d078741d..4a1b24a9dd61 100644
>>> --- a/arch/powerpc/kernel/machine_kexec.c
>>> +++ b/arch/powerpc/kernel/machine_kexec.c
>>> @@ -95,16 +95,14 @@ void arch_crash_save_vmcoreinfo(void)
>>>   */
>>>  void machine_kexec(struct kimage *image)
>>>  {
>>> -	int save_ftrace_enabled;
>>> -
>>> -	save_ftrace_enabled =3D __ftrace_enabled_save();
>>> +	get_paca()->ftrace_disabled =3D 1;
>>
>> This doesn't compile on 32-bit:
>>
>>   Failed: powerpc-next/corenet32_smp_defconfig/powerpc-5.3		(http://kiss=
kb.ozlabs.ibm.com/kisskb/buildresult/13314085/log/)
>>     /kisskb/src/arch/powerpc/kernel/machine_kexec.c:105:12: error: inval=
id type argument of '->' (have 'int')
>>     /kisskb/src/arch/powerpc/kernel/machine_kexec.c:98:12: error: invali=
d type argument of '->' (have 'int')
>>     /kisskb/src/arch/powerpc/kernel/machine_kexec.c:98:2: error: implici=
t declaration of function 'get_paca' [-Werror=3Dimplicit-function-declarati=
on]

Hmm... pmac32_defconfig built fine for me, so I thought we are ok there.

>>
>>
>> A wrapper is probably best that does nothing on 32-bit.
>=20
> Actually it should probably do __ftrace_enabled_save() etc. on 32-bit,
> like the existing code does.

Agree. In hindsight, I'm not updating ftrace_32.S, so I think I will=20
gate this with CONFIG_PPC64.

Thanks,
Naveen

=