Re: [PATCH] powerpc/smp: Handle missing ibm,thread-groups in parse_thread_groups()

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

Shrikanth Hegde <sshegde@linux.ibm.com> writes:

> Hi Ritesh,
>
> +cc nathan, Kees,
>
> On 11/10/26 7:13 PM, Ritesh Harjani (IBM) wrote:
>> Power systems can have ibm,thread-groups properly absent like in one of
>> the PowerNV Power9 boxes where there was a warning splat reported on
>> 7.4-rc2:
>> 
>>    WARNING: mm/slub.c:5459 at ___kmalloc_large_node+0x174/0x1a0, CPU#124: swapper/124/1
>>    ...
>>    Call Trace:
>>     __kmalloc_noprof+0x490/0x690
>>     _kzalloc_noprof.constprop.0+0x1c/0x7c
>>     init_thread_group_cache_map+0xd0/0x2d4
>>     smp_prepare_cpus+0x2bc/0x484
>>     kernel_init_freeable+0x168/0x3c4
>>     kernel_init+0x34/0x1ac
>> 
>> This happens because today we don't check for whether the properly is
>> present or not and directly pass the return value of
>> of_property_count_u32_elems(), to the allocator.
>> 
>> This went unnoticed because earlier kcalloc() caught the overflow due to
>> check_mul_overflow() check and returned NULL.
>> But since commit 0af298e62e5c ("treewide: refresh kmalloc_obj()
>> conversions") switched this call to kzalloc_objs(), size_mul() saturates
>> the size to SIZE_MAX instead and we now get a warning at boot.
>> 
>> Bail out early if the property is missing or empty. Follow the return
>> value as documented in kernel doc of parse_thread_groups() function.
>> 
>> Fixes: 790a1662d3a2 ("powerpc/smp: Parse ibm,thread-groups with multiple properties")
>> Reported-by: Madhavan Srinivasan <maddy@linux.ibm.com>
>> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
>> ---
>>   arch/powerpc/kernel/smp.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>> 
>> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
>> index 7a25eaa59e62..9a0f63e43821 100644
>> --- a/arch/powerpc/kernel/smp.c
>> +++ b/arch/powerpc/kernel/smp.c
>> @@ -824,6 +824,10 @@ static int parse_thread_groups(struct device_node *dn,
>>   	int i = 0;
>> 
>>   	count = of_property_count_u32_elems(dn, "ibm,thread-groups");
>> +	if (count < 0)
>> +		return count;
>> +	if (!count)
>> +		return -ENODATA;
>
> This zero count check is not necessary.
>

yes, not strictly necessary, but good to have. 

>>   	thread_group_array = kzalloc_objs(u32, count);
>>   	if (!thread_group_array)
>>   		return -ENOMEM;
>> --
>> 2.39.5
>> 
>
> Nathan reported the same issue on QEMU.The same symptoms.
>
> https://lore.kernel.org/all/20261109-powerpc-smp-handle-count-err-v1-1-e777fde7f71a@kernel.org/

I didn't notice this. Thanks for pointing it out. In that case let's drop
this patch.

-ritesh