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

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Date:   Thu, 22 Dec 2016 22:37:33 +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 2/2] mm/memblock.c: check return value of
 memblock_reserve() in memblock_virt_alloc_internal()

On Thu, Dec 22, 2016 at 10:15:20AM +0100, Michal Hocko wrote:
>On Wed 21-12-16 23:30:33, Wei Yang wrote:
>> memblock_reserve() would add a new range to memblock.reserved in case the
>> new range is not totally covered by any of the current memblock.reserved
>> range. If the memblock.reserved is full and can't resize,
>> memblock_reserve() would fail.
>> 
>> This doesn't happen in real world now, I observed this during code review.
>> While theoretically, it has the chance to happen. And if it happens, others
>> would think this range of memory is still available and may corrupt the
>> memory.
>
>OK, this explains it much better than the previous version! The silent
>memory corruption is indeed too hard to debug to have this open even
>when the issue is theoretical.
>

Thanks~ Have a nice day:-)

>> This patch checks the return value and goto "done" after it succeeds.
>> 
>> Signed-off-by: Wei Yang <richard.weiyang@...il.com>
>
>Acked-by: Michal Hocko <mhocko@...e.com>
>
>Thanks!
>
>> ---
>>  mm/memblock.c | 6 ++----
>>  1 file changed, 2 insertions(+), 4 deletions(-)
>> 
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index 4929e06..d0f2c96 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -1274,18 +1274,17 @@ static void * __init memblock_virt_alloc_internal(
>>  
>>  	if (max_addr > memblock.current_limit)
>>  		max_addr = memblock.current_limit;
>> -
>>  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;
>>  	}
>>  
>> @@ -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
>
>-- 
>Michal Hocko
>SUSE Labs

-- 
Wei Yang
Help you, Help me