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 10:01:11 +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 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".

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

-- 

Thanks,

David / dhildenb