Re: [PATCH v2 1/2] xen/riscv: initialize bootinfo from dtb

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.10.2024 09:50, oleksii.kurochko@xxxxxxxxx wrote:
> On Tue, 2024-10-15 at 14:32 +0200, Jan Beulich wrote:
>> On 15.10.2024 11:11, oleksii.kurochko@xxxxxxxxx wrote:
>>> On Tue, 2024-10-15 at 08:33 +0200, Jan Beulich wrote:
>>>> On 10.10.2024 17:30, Oleksii Kurochko wrote:
>>>>> --- a/xen/arch/riscv/setup.c
>>>>> +++ b/xen/arch/riscv/setup.c
>>>>> @@ -50,6 +50,8 @@ void __init noreturn start_xen(unsigned long
>>>>> bootcpu_id,
>>>>>                            _end - _start, false) )
>>>>>          panic("Failed to add BOOTMOD_XEN\n");
>>>>>  
>>>>> +    BUG_ON(!boot_fdt_info(device_tree_flattened, dtb_addr));
>>>>
>>>> We generally aim at avoiding side effects in BUG_ON() (or
>>>> ASSERT()).
>>>> With
>>>>
>>>>     if (!boot_fdt_info(device_tree_flattened, dtb_addr))
>>>>         BUG();
>>>>
>>>> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>>
>>>> I can make the adjustment while committing, if desired.
>>> It would be great if these changes could be made during the commit.
>>
>> I've committed it with the adjustment, 
> Thanks!
> 
>> yet once again I wondered: Why not
>> panic()?
> It could be panic() here; there's no specific reason. I agree that
> using BUG() here isn't logically correct, as technically, a size of
> zero for the FDT isn't a bug but rather indicates that someone provided
> an incorrect FDT to Xen.
> 
> I will use panic() in the future for such cases.
> 
> It’s not always clear what should be used and where. Perhaps it would
> be helpful to add some explanation somewhere.

My rule of thumb: During init and when the call stack / register state
aren't relevant to understand the details of the issue, use panic().

Jan