linux-kernel - Re: [PATCH V2 2/2] mm/memblock.c: check return value of memblock_reserve() in memblock_virt_alloc

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Message-ID: <20161220164823.GB13224@vultr.guest>
Date:   Tue, 20 Dec 2016 16:48:23 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Wei Yang <richard.weiyang@...il.com>, trivial@...nel.org,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 2/2] mm/memblock.c: check return value of
 memblock_reserve() in memblock_virt_alloc_internal()

On Mon, Dec 19, 2016 at 04:21:57PM +0100, Michal Hocko wrote:
>On Sun 18-12-16 14:47:50, Wei Yang wrote:
>> memblock_reserve() may fail in case there is not enough regions.
>
>Have you seen this happenning in the real setups or this is a by-review
>driven change?

This is a by-review driven change.

>[...]
>>  again:
>>  	alloc = memblock_find_in_range_node(size, align, min_addr, max_addr,
>>  					    nid, flags);
>> -	if (alloc)
>> +	if (alloc && !memblock_reserve(alloc, size))
>>  		goto done;
>>  
>>  	if (nid != NUMA_NO_NODE) {
>>  		alloc = memblock_find_in_range_node(size, align, min_addr,
>>  						    max_addr, NUMA_NO_NODE,
>>  						    flags);
>> -		if (alloc)
>> +		if (alloc && !memblock_reserve(alloc, size))
>>  			goto done;
>>  	}
>
>This doesn't look right. You can end up leaking the first allocated
>range.
>

Hmm... why?

If first memblock_reserve() succeed, it will jump to done, so that no 2nd
allocation.
If the second executes, it means the first allocation failed.
memblock_find_in_range_node() doesn't modify the memblock, it just tell you
there is a proper memory region available.

>>  
>> @@ -1303,7 +1302,6 @@ static void * __init memblock_virt_alloc_internal(
>>  
>>  	return NULL;
>>  done:
>> -	memblock_reserve(alloc, size);
>>  	ptr = phys_to_virt(alloc);
>>  	memset(ptr, 0, size);
>
>
>>  
>> -- 
>> 2.5.0
>> 
>> --
>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>> the body to majordomo@...ck.org.  For more info on Linux MM,
>> see: http://www.linux-mm.org/ .
>> Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
>
>-- 
>Michal Hocko
>SUSE Labs

-- 
Wei Yang
Help you, Help me