linux-kernel - Re: [Bug fix PATCH] resource: Reusing a resource structure allocated by bootmem

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Date:	Tue, 16 Apr 2013 09:34:59 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	Toshi Kani <toshi.kani@...com>
CC:	<akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>,
	<rientjes@...gle.com>, <linuxram@...ibm.com>
Subject: Re: [Bug fix PATCH] resource: Reusing a resource structure allocated
 by bootmem

Hi Toshi,

2013/04/16 5:01, Toshi Kani wrote:
> On Mon, 2013-04-15 at 11:15 +0900, Yasuaki Ishimatsu wrote:
>> When hot removing memory presented at boot time, following messages are shown:
>
> :
>
>> The reason why the messages are shown is to release a resource structure,
>> allocated by bootmem, by kfree(). So when we release a resource structure,
>> we should check whether it is allocated by bootmem or not.
>>
>> But even if we know a resource structure is allocated by bootmem, we cannot
>> release it since SLxB cannot treat it. So for reusing a resource structure,
>> this patch remembers it by using bootmem_resource as follows:
>>
>> When releasing a resource structure by free_resource(), free_resource() checks
>> whether the resource structure is allocated by bootmem or not. If it is
>> allocated by bootmem, free_resource() adds it to bootmem_resource. If it is
>> not allocated by bootmem, free_resource() release it by kfree().
>>
>> And when getting a new resource structure by get_resource(), get_resource()
>> checks whether bootmem_resource has released resource structures or not. If
>> there is a released resource structure, get_resource() returns it. If there is
>> not a releaed resource structure, get_resource() returns new resource structure
>> allocated by kzalloc().
>
> Thanks for fixing this existing issue that also needed to be addressed.
> I am not able to test this particular case in my test env, so I did not
> notice it.
>

> Can you update this patch to base off of the patch below?  Otherwise, it
> won't apply cleanly.
> https://lkml.org/lkml/2013/4/11/694

O.K. I'll update it.

>
> More comments below.
>
>> Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
>> ---
>> This patch is baseg on following Toshi's works:
>> Support memory hot-delete to boot memory
>>    https://lkml.org/lkml/2013/4/10/469
>>
>>   kernel/resource.c |   72 +++++++++++++++++++++++++++++++++++++++++++---------
>>   1 files changed, 59 insertions(+), 13 deletions(-)
>>
>> diff --git a/kernel/resource.c b/kernel/resource.c
>> index 16bfd39..152e9aa 100644
>> --- a/kernel/resource.c
>> +++ b/kernel/resource.c
>> @@ -21,6 +21,7 @@
>>   #include <linux/seq_file.h>
>>   #include <linux/device.h>
>>   #include <linux/pfn.h>
>> +#include <linux/mm.h>
>>   #include <asm/io.h>
>>
>>
>> @@ -50,6 +51,16 @@ struct resource_constraint {
>>
>>   static DEFINE_RWLOCK(resource_lock);
>>
>> +/*
>> + * For memory hotplug, there is no way to free resource entries allocated
>> + * by boot mem after the system is up. So for reusing the resource entry
>> + * we need to remember the resource.
>> + */
>> +struct resource bootmem_resource = {
>> +	.sibling = NULL,
>> +};
>> +static DEFINE_SPINLOCK(bootmem_resource_lock);
>> +
>>   static void *r_next(struct seq_file *m, void *v, loff_t *pos)
>>   {
>>   	struct resource *p = v;
>> @@ -151,6 +162,42 @@ __initcall(ioresources_init);
>>
>>   #endif /* CONFIG_PROC_FS */
>>
>> +static void __free_resource(struct resource *res)
>> +{
>> +	struct resource *next_res = bootmem_resource.sibling;
>> +
>> +	bootmem_resource.sibling = res;
>> +	res->sibling = next_res;
>> +}
>> +
>> +static void free_resource(struct resource *res)
>> +{
>

> You need to add the following if-statement here.  Otherwise it hits a
> page fault when res is NULL.  This case happens when a resource entry
> splits into two entries.
>
> 	if (!res)
> 		return;

I'll update it.

>
>> +	if (PageReserved(virt_to_page(res))) {
>> +		spin_lock(&bootmem_resource_lock);
>> +		__free_resource(res);
>

> How about simply updating the link here, instead of having it done in
> __free_resource()?  I think it makes it more consistent with
> get_resource().
>
> 		res->sibling = bootmem_resource.sibling;
> 		bootmem_resource.sibling = res;

I'll update it.

Thanks,
Yasuaki Ishimatsu

>
> Thanks,
> -Toshi
>
>> +		spin_unlock(&bootmem_resource_lock);
>> +	} else {
>> +		kfree(res);
>> +	}
>> +}
>
>
>


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