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Date:   Tue, 20 Jun 2023 15:04:55 +0800
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Subject: Re: [PATCH] memblock: Add error message when memblock_can_resize is
 not ready
To:     Mike Rapoport <rppt@kernel.org>
Cc:     akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <20230614131746.3670303-1-songshuaishuai@tinylab.org>
 <20230614160710.GH52412@kernel.org>
From:   Song Shuai <songshuaishuai@tinylab.org>
In-Reply-To: <20230614160710.GH52412@kernel.org>
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Sorry for not replying to you in time

在 2023/6/15 00:07, Mike Rapoport 写道:
> Hi,
> 
> On Wed, Jun 14, 2023 at 09:17:46PM +0800, Song Shuai wrote:
>> The memblock APIs are always correct, thus the callers usually don't
>> handle the return code. But the failure caused by unready memblock_can_resize
>> is hard to recognize without the return code. Like this piece of log:
> 
> Please make it clear that failure is in memblock_double_array(), e.g.
> 

Having numerous memblock reservations at early boot where 
memblock_can_resize is unset
may exhaust the INIT_MEMBLOCK_REGIONS sized memblock.reserved regions 
and try to
double the region array via memblock_double_array() which fails and 
returns -1 to the caller.

You can find the numerous memblock reservations reported by this commit
24cc61d8cb5a ("arm64: memblock: don't permit memblock resizing until 
linear mapping is up").
And the similar test sense can be simulated by a constructed dtb with 
numerous discrete
/memreserve/ or /reserved-memory regions.

> But when memblock_double_array() is called before memblock_can_resize
> is true, it is hard to understand the actual reason for the failure.
> 
>>
>> ```
>> [    0.000000] memblock_phys_alloc_range: 4096 bytes align=0x1000 from=0x0000000000000000 max_addr=0x0000000000000000 alloc_pmd_fixmap+0x14/0x1c
>> [    0.000000] memblock_reserve: [0x000000017ffff000-0x000000017fffffff] memblock_alloc_range_nid+0xb8/0x128
>> [    0.000000] Oops - store (or AMO) access fault [#1]
>> ```
>>
>> So add an error message for this kind of failure:
>>
>> ```
>> [    0.000000] memblock_phys_alloc_range: 4096 bytes align=0x1000 from=0x0000000000000000 max_addr=0x0000000000000000 alloc_pmd_fixmap+0x14/0x1c
>> [    0.000000] memblock_reserve: [0x000000017ffff000-0x000000017fffffff] memblock_alloc_range_nid+0xb8/0x128
>> [    0.000000] memblock: Can't double reserved array for area start 0x000000017ffff000 size 4096
>> [    0.000000] Oops - store (or AMO) access fault [#1]
>> ```
>>
>> Signed-off-by: Song Shuai <songshuaishuai@tinylab.org>
>> ---
>>   mm/memblock.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index 3feafea06ab2..ab952a164f62 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -418,8 +418,11 @@ static int __init_memblock memblock_double_array(struct memblock_type *type,
>>   	/* We don't allow resizing until we know about the reserved regions
>>   	 * of memory that aren't suitable for allocation
>>   	 */
>> -	if (!memblock_can_resize)
>> +	if (!memblock_can_resize) {
>> +		pr_err("memblock: Can't double %s array for area start %pa size %ld\n",
>> +			type->name, &new_area_start, (unsigned long)new_area_size);
> 
> Most of the time memblock uses %llu and cast to u64 to print size, please
> make this consistent.
I will fix it in next version if the above description is ok for you.
> 
>>   		return -1;
>> +	}
>>   
>>   	/* Calculate new doubled size */
>>   	old_size = type->max * sizeof(struct memblock_region);
>> -- 
>> 2.20.1
>>
>>
> 

-- 
Thanks
Song Shuai