Re: [Xen-devel] A memory leak problem in xen-blkback module

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

El 15/09/14 a les 11.55, Roger Pau Monné ha escrit:
> El 12/09/14 a les 8.58, Chentao(Boby) ha escrit:
>> Hi Konrad,
>>
>>     I find a memory leak problem in xen-blkback module of linux-3.14.4 
>> release, and the newest 3.17-rc4 also has the same problem. The problem will 
>> occur in below condition.
>>
>>     In xen_blkbk_map function, first get_free_page from balloon or the list 
>> of blkif free pages, then map this page. If get_free_page succeed, but map 
>> failed,
>> the grant handle corresponding to this page will be assigned to 
>> BLKBACK_INVALID_HANDLE. Because map failed, it will execute xen_blkbk_unmap 
>> to retrieve resources.
>> But in xen_blkbk_unmap function, if the grant handle of a page is 
>> BLKBACK_INVALID_HANDLE, it will continue to next loop to execute unmap and 
>> put_free_pages.
>> Only executes put_free_pages, these pages will be returned to the list of 
>> blkif free pages and at last be returned to balloon.
>>
>>     Make a summary, in the condition of get_free_page succeed but map 
>> failed, the page will be leaked from balloon or the list of blkif free 
>> pages. I have a immature thought,
>> in xen_blkbk_unmap funtion, when judge the grant handle of a page is 
>> BLKBACK_INVALID_HANDLE, can we execute put_free_pages to retrieve this one 
>> page?
>>
>>     Just like below:
>>     if (pages[i]->handle == BLKBACK_INVALID_HANDLE) {
>>         put_free_pages(blkif, pages[i]->page, 1);
> 
> This is not correct, and will fail to compile AFAICT. put_free_pages 
> expects an array of pointers to page structs and you are passing a 
> pointer to a page struct.
> 
> I have the following patch, which I think solves the problem. I've 
> placed the free_pages call in xen_blkbk_map itself, but it could also 
> be done in xen_blkbk_map_unmap.
> 
> ---
> commit 879ebb502e2f72279553bb0a85cc885ec492a0c1
> Author: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> Date:   Mon Sep 15 11:01:40 2014 +0200
> 
>     xen-blkback: fix leak on grant map error path
>     
>     Fix leaking a page when a grant mapping has failed.
>     
>     Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>     Reported by: Tao Chen <boby.chen@xxxxxxxxxx>
>     ---
>     This patch should be backported to stable branches.

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