Re: [patch] x86, pat: freeing invalid memtype messages

[Xiaotian Feng <dfeng@redhat.com>]

On 06/18/2010 12:17 AM, Marcin Slusarz wrote:
> On Thu, Jun 17, 2010 at 03:45:59PM +0200, Dan Carpenter wrote:
>> Commit 20413f27163 "x86, pat: Fix memory leak in free_memtype" added an
>> error message in free_memtype() if rbt_memtype_erase() returns NULL.
>> The problem is that if CONFIG_X86_PAT is enabled, we use a different
>> implimentation of rbt_memtype_erase() that always returns NULL.
>>
>> I've modified rbt_memtype_erase() to return an ERR_PTR() on errors and
>> made free_memtype() check for that instead.
>>
>> Addresses:  https://bugzilla.kernel.org/show_bug.cgi?id=16205
>>
>> Signed-off-by: Dan Carpenter<error27@gmail.com>
>
> This patch is probably ok, but it does not address my bug.
> I have CONFIG_X86_PAT=y, so rbt_memtype_erase does not always return NULL.

The reason for the warning "swapper:1 freeing invalid memtype \ 
bf799000-bf79a000"
could be two callers reserved "bf799000 - bf79a000". The two callers has 
the same reserve area and same memtype, so the sencond caller will also 
success to reserve "bf799000 - bf79a000".

But at the free stage, if one caller freed "bf799000 - bf79a000", then 
another caller is trying to free "bf799000 - bf79a000", can not find it 
in the rbtree, so pop up an invalid memtype.

>
>> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
>> index acc15b2..81b7735 100644
>> --- a/arch/x86/mm/pat.c
>> +++ b/arch/x86/mm/pat.c
>> @@ -359,10 +359,10 @@ int free_memtype(u64 start, u64 end)
>>   	entry = rbt_memtype_erase(start, end);
>>   	spin_unlock(&memtype_lock);
>>
>> -	if (!entry) {
>> +	if (IS_ERR(entry)) {
>>   		printk(KERN_INFO "%s:%d freeing invalid memtype %Lx-%Lx\n",
>>   			current->comm, current->pid, start, end);
>> -		return -EINVAL;
>> +		return PTR_ERR(entry);
>>   	}
>>
>>   	kfree(entry);
>> diff --git a/arch/x86/mm/pat_rbtree.c b/arch/x86/mm/pat_rbtree.c
>> index f537087..90e5cbe 100644
>> --- a/arch/x86/mm/pat_rbtree.c
>> +++ b/arch/x86/mm/pat_rbtree.c
>> @@ -236,8 +236,10 @@ struct memtype *rbt_memtype_erase(u64 start, u64 end)
>>   	struct memtype *data;
>>
>>   	data = memtype_rb_exact_match(&memtype_rbroot, start, end);
>> -	if (!data)
>> +	if (!data) {
>> +		data = ERR_PTR(-EINVAL);
>>   		goto out;
>> +	}
>>
>>   	rb_erase(&data->rb,&memtype_rbroot);
>>   out:
>>
>>
>