Re: [PATCH] iio: core: WARN in case sample bits do not fit storage bits

[Marek Vasut <marex@denx.de>]

On 3/22/22 10:49, Andy Shevchenko wrote:
> On Tue, Mar 22, 2022 at 08:43:10AM +0100, Nuno Sá wrote:
>> On Mon, 2022-03-21 at 20:46 +0100, Marek Vasut wrote:
>>> On 3/21/22 17:10, Andy Shevchenko wrote:
>>>> On Mon, Mar 21, 2022 at 03:46:51PM +0100, Marek Vasut wrote:
>>>>> On 3/21/22 11:40, Andy Shevchenko wrote:
>>>>>> On Sun, Mar 20, 2022 at 07:15:42PM +0100, Marek Vasut wrote:
>>>>>>> Add runtime check to verify whether storagebits are at least
>>>>>>> as big
>>>>>>> as shifted realbits. This should help spot broken drivers
>>>>>>> which may
>>>>>>> set realbits + shift above storagebits.
>>>>>>
>>>>>> Thanks!
>>>>>>
>>>>>> ...
>>>>>>
>>>>>>> +                       /* Verify that sample bits fit into
>>>>>>> storage */
>>>>>>> +                       WARN_ON(channels[i].scan_type.storage
>>>>>>> bits <
>>>>>>> +                               channels[i].scan_type.realbit
>>>>>>> s +
>>>>>>> +                               channels[i].scan_type.shift);
>>>>>>
>>>>>> Not sure WARN is a good level (it might be fatal on some setups
>>>>>> and we won't that),
>>>>>> besides the fact that we may use dev_WARN(). Perhaps dev_warn()
>>>>>> would suffice?
>>>>>
>>>>> I was actually thinking about BUG(), but that might crash
>>>>> existing systems.
>>>>> I think we want a strong indicator that something wrong is going
>>>>> on which
>>>>> must be fixed and the splat produced by WARN_ON() is a good
>>>>> indicator of
>>>>> that. It also does not crash existing systems,
>>>>
>>>> It does crash _some_ of them, unfortunately.
>>>
>>> Details please ?
>>>
>>> WARN_ON() shouldn't cause crash outright, or do I miss something ?
>>
>> Arghh, completely forgot about this... Andy is right, maybe there are
>> other cases (in which case, it would be nice to share :D), but this one
>> is definitely one of them:
>>
>> https://elixir.bootlin.com/linux/latest/source/kernel/panic.c#L579
>>
>> You can have a cmdline parameter to panic on _WARN() and some systems
>> may have it.
> 
> Yes, I meant panic on warning.
> 
> And I can't imagine that this driver can be system critical to the extent
> that we have to crash the system.

Is there something which does trigger a backtrace, but without 
panic()ing the system ?