Re: [PATCH v2 1/5] drivers/base/memory: Remove unneeded check in remove_memory_block_devices

[David Hildenbrand]

On 25.06.19 10:09, Oscar Salvador wrote:
> On Tue, Jun 25, 2019 at 10:03:31AM +0200, David Hildenbrand wrote:
>> On 25.06.19 10:01, David Hildenbrand wrote:
>>> On 25.06.19 09:52, Oscar Salvador wrote:
>>>> remove_memory_block_devices() checks for the range to be aligned
>>>> to memory_block_size_bytes, which is our current memory block size,
>>>> and WARNs_ON and bails out if it is not.
>>>>
>>>> This is the right to do, but we do already do that in try_remove_memory(),
>>>> where remove_memory_block_devices() gets called from, and we even are
>>>> more strict in try_remove_memory, since we directly BUG_ON in case the range
>>>> is not properly aligned.
>>>>
>>>> Since remove_memory_block_devices() is only called from try_remove_memory(),
>>>> we can safely drop the check here.
>>>>
>>>> To be honest, I am not sure if we should kill the system in case we cannot
>>>> remove memory.
>>>> I tend to think that WARN_ON and return and error is better.
>>>
>>> I failed to parse this sentence.
>>>
>>>>
>>>> Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
>>>> ---
>>>>  drivers/base/memory.c | 4 ----
>>>>  1 file changed, 4 deletions(-)
>>>>
>>>> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
>>>> index 826dd76f662e..07ba731beb42 100644
>>>> --- a/drivers/base/memory.c
>>>> +++ b/drivers/base/memory.c
>>>> @@ -771,10 +771,6 @@ void remove_memory_block_devices(unsigned long start, unsigned long size)
>>>>  	struct memory_block *mem;
>>>>  	int block_id;
>>>>  
>>>> -	if (WARN_ON_ONCE(!IS_ALIGNED(start, memory_block_size_bytes()) ||
>>>> -			 !IS_ALIGNED(size, memory_block_size_bytes())))
>>>> -		return;
>>>> -
>>>>  	mutex_lock(&mem_sysfs_mutex);
>>>>  	for (block_id = start_block_id; block_id != end_block_id; block_id++) {
>>>>  		mem = find_memory_block_by_id(block_id, NULL);
>>>>
>>>
>>> As I said when I introduced this, I prefer to have such duplicate checks
>>> in place in case we have dependent code splattered over different files.
>>> (especially mm/ vs. drivers/base). Such simple checks avoid to document
>>> "start and size have to be aligned to memory blocks".
>>
>> Lol, I even documented it as well. So yeah, if you're going to drop this
>> once, also drop the one in create_memory_block_devices().
> 
> TBH, I would not mind sticking with it.
> What sticked out the most was that in the previous check, we BUG_on while
> here we just print out a warning, so it seemed quite "inconsistent" to me.
> 
> And I only stumbled upon this when I was testing a kernel module that
> hot-removed memory in a different granularity.
> 
> Anyway, I do not really feel strong here, I can perfectly drop this patch as I
> would rather have the focus in the following-up patches, which are the important
> ones IMO.

Whetever you prefer, I can live with either :)

(yes, separating this patch from the others makes sense)

-- 

Thanks,

David / dhildenb