linux-kernel - Re: [PATCH v2 1/5] drivers/base/memory: Remove unneeded check in remove_memory_block

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Date:   Tue, 25 Jun 2019 10:03:31 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>, akpm@...ux-foundation.org
Cc:     mhocko@...e.com, dan.j.williams@...el.com,
        pasha.tatashin@...een.com, Jonathan.Cameron@...wei.com,
        anshuman.khandual@....com, vbabka@...e.cz, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/5] drivers/base/memory: Remove unneeded check in
 remove_memory_block_devices

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@...e.de>
>> ---
>>  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().

> 
> If you still insist, then also remove the same sequence from
> create_memory_block_devices().
> 


-- 

Thanks,

David / dhildenb