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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Sep 30, 2014 at 05:23:13PM +0200, Roger Pau Monné wrote:
> 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.
> 
> Ping?
> 

Reviewed. Testing it and once that is done will send it for Jens. Thanks!

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