Hi Greg,
On 2018/11/22 19:26, Greg Kroah-Hartman wrote:
> On Thu, Nov 22, 2018 at 07:11:08PM +0800, Gao Xiang wrote:
>> Hi Greg,
>>
>> On 2018/11/22 19:05, Greg Kroah-Hartman wrote:
>>> On Thu, Nov 22, 2018 at 06:34:10PM +0800, Gao Xiang wrote:
>>>> Hi Greg,
>>>>
>>>> On 2018/11/22 18:23, Greg Kroah-Hartman wrote:
>>>>>> +
>>>>>> + DBG_BUGON(work->nr_pages);
>>>>>> + DBG_BUGON(work->vcnt);
>>>>> How can these ever be triggered? I understand the need for debugging
>>>>> code when you are writing code, but at this point it shouldn't be needed
>>>>> anymore, right?
>>>>
>>>> I need to avoid some fields is not 0 when the new workgroup is created
>>>> (because
>>>> work->nr_pages and work->vcnt == 0 usually after the previous workgroup is
>>>> freed).
>>>> But that is not obvious, it is promised by the current logic.
>>>
>>> Then delete these lines if they can never happen :)
>>
>> I don't know how to observe such a race in our beta test and community users.
>
> /*
> * Let developers know something went really wrong with their
> * initialization code
> */
> if (!work->nr_pages) {
> pr_err("nr_pages == NULL!");
> WARN_ON(1);
> }
> if (!work->vcnt) {
> pr_err("vcnt == NULL!");
> WARN_ON(1);
> }
>
> or something like that.
>
> Don't make people rebuild your code with different options for
> debugging. That will never work in the 'real world' when people start
> using the code. You need to have things enabled for people all the
> time, which is why we have dynamic debugging in the kernel now, and not
> a zillion different "DRIVER_DEBUG" build options anymore.
>
>> Because if the kernel is crashed, we could collect the whole kernel dump to
>> observe the memory
>> and all registers, if we only have some warning, it will be not easy to get
>> the state as early as possible.
>
> When the kernel crashes, geting a dump is hard on almost all hardware.
> It is only rare systems that you can get a kernel dump.
This piece of code is already used in our hisilicon beta test, all memorydump,
registers, stack can be collected.
Apart from that, I observed many f2fs bugs are observed in this way and
many erofs bugs are collected in that way...sigh...
Thanks,
Gao Xiang
>
> thanks,
>
> greg k-h
>
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