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 10:15:20 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     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 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.

> 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