linux-kernel - RE: Re: [PATCH] UBI: fix memory leak when use fastmap

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Date:	Thu, 2 May 2013 16:30:01 +0800
From:	wang.bo116@....com.cn
To:	richard -rw- weinberger <richard.weinberger@...il.com>
Cc:	artem.bityutskiy@...ux.intel.com, cui.yunfeng@....com.cn,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	liu.dong3@....com.cn
Subject: RE: Re: [PATCH] UBI: fix memory leak when use fastmap

> Hi!
> 
> On Tue, Apr 16, 2013 at 10:53 AM,  <wang.bo116@....com.cn> wrote:
> > Hello,
> >         Sorry, there is still something wrong with the previous 
patch's
> > format, try to submit it again. When use ubi fastmap, there is a 
memory
> > leak which will make destroy_ai() fail to free the slab alloced in
> > scan_fast(). The following patch fix this problem by use a temporary
> > "ubi_attach_info" variable in scan_fast().
> 
> Thanks a lot for your patch!
> 
> Did you test it well?
> We need to make sure that it does the right thing for the following 
cases:
> 1. fastmap disabled, attaching a non-fastmap volume
> 1. fastmap disabled, attaching a fastmap volume
> 3. fastmap enabled, attaching a non-fastmap volume
> 4. fastmap enablled, attaching a fastmap volume
> 
> --
> Thanks,
> //richard

Thanks for your advice. I consider this problem like this:
1: if fastmap not config, ubi_attach() just call scan_all(ubi, ai, 0), 
there is nothing changed, so there is all right.

2: if fastmap config, and force_scan is 0, ubi_attach() will call 
scan_fast(), when scan_fast() return, temp ai used in scan_fast() has been 
free, and there will be two conditions:
A: scan_fast() return UBI_NO_FASTMAP(may be flash is empty or attaching a 
non-fastmap volume), all ubi_attach() need is to call scan_all(ubi, ai, 0) 
to scan all blocks. 
B: scan_fast() return UBI_BAD_FASTMAP, ubi_attach() first free ai used in 
ubi_scan_fastmap(), then alloc a clean ai, at last call scan_all(ubi, ai, 
0) to scan all blocks.

3: if fastmap config, and force_scan is 1, just call scan_all(ubi, ai, 0).

This patch pass the following cases(include attach and detach):
1. fastmap config, flash is empty,fm_autoconvert is 1.
2. fastmap config, flash is empty,fm_autoconvert is 0.
3. fastmap config, attaching a fastmap volume
4. fastmap config, attaching a bad fastmap volume
5. fastmap config, attaching a non-fastmap volume
6. fastmap not config, attaching a fastmap volume
7. fastmap not config, attaching a non-fastmap volume
8. fastmap not config, flash is empty.

By the way, the problem may cause ubi_attach() fail after ubi detach when 
CONFIG_DEBUG_VM config. 
The reason is that ubi_attach() will alloc a slab cache, but the 
kmem_cache_sanity_check() will find the slab cache is already exist(not 
been free after last detach), so slab cache alloc fail, and ubi_attach() 
fail, too.

Thanks 
--wangbo
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