linux-kernel - Re: [PATCH] memblock: Make sure reserved.regions is freed really

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Message-ID: <CAE9FiQUYsPFPnQvTsy9u3inM3hP5uWYtCRJMvQ=MvR7fCJTqzg@mail.gmail.com>
Date:	Mon, 18 Jun 2012 15:58:52 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH] memblock: Make sure reserved.regions is freed really

On Mon, Jun 18, 2012 at 3:05 PM, Tejun Heo <tj@...nel.org> wrote:
> Hello, Yinghai.
>
> On Fri, Jun 15, 2012 at 08:12:11PM -0700, Yinghai Lu wrote:
>> memblock_free() would double reserved.regions too, so we could free
>> old range for reserved.regions.
>>
>> So need to check that regions get doubled. If it is doubled, we need to
>> free it.
>>
>> Cc: Tejun Heo <tj@...nel.org>
>> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>>
>> ---
>>  mm/memblock.c |   23 +++++++++++++++++++++--
>>  1 file changed, 21 insertions(+), 2 deletions(-)
>>
>> Index: linux-2.6/mm/memblock.c
>> ===================================================================
>> --- linux-2.6.orig/mm/memblock.c
>> +++ linux-2.6/mm/memblock.c
>> @@ -148,11 +148,26 @@ phys_addr_t __init_memblock memblock_fin
>>   */
>>  int __init_memblock memblock_free_reserved_regions(void)
>>  {
>> +     struct memblock_region *r;
>> +     int ret;
>> +
>>       if (memblock.reserved.regions == memblock_reserved_init_regions)
>>               return 0;
>>
>> -     return memblock_free(__pa(memblock.reserved.regions),
>> -              sizeof(struct memblock_region) * memblock.reserved.max);
>> +     /*
>> +      * During memblock_free, reserved.regions could be doubled,
>> +      * try to check with old one for checking, and need to free the new one.
>> +      */
>> +     do {
>> +             r = memblock.reserved.regions;
>> +             ret = memblock_free(__pa(memblock.reserved.regions),
>> +                     sizeof(struct memblock_region) * memblock.reserved.max);
>> +
>> +             if (ret)
>> +                     break;
>> +     } while (memblock.reserved.regions != r);
>> +
>> +     return ret;
>>  }
>
> Hmmm... nice catch but I think it's a bit complex and ugly.  In this
> case, we *know* that the region isn't gonna be split.  Maybe a better
> option is to add something like the following?

how do you know __pa(memblock.reserved.regions) would not be merged
with other entries
in reserved.regions?

>
> void memblock_remove_region_by_ptr(struct memblock_type *type,
>                                   struct memblock_region *r)
> {
>        WARN_ON(/* make sure @r is inside @type->regions */);
>        memblock_remove_region(type, r - type->regions);
> }

you want to change

/*
 * Free memblock.reserved.regions
 */
int __init_memblock memblock_free_reserved_regions(void)
{
        if (memblock.reserved.regions == memblock_reserved_init_regions)
                return 0;

        return memblock_free(__pa(memblock.reserved.regions),
                 sizeof(struct memblock_region) * memblock.reserved.max);
}

to use memblock_remove_region_by_ptr() ?

Thanks

Yinghai
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