linux-kernel - Re: [PATCH v2 2/2] btrfs-progs: Fix up memory leakage

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Date:	Tue, 25 Sep 2012 19:14:30 +0200
From:	Goffredo Baroncelli <kreijack@...ero.it>
To:	zwu.kernel@...il.com, linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, jbacik@...ionio.com, dave@...os.cz,
	linuxram@...ux.vnet.ibm.com, Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 2/2] btrfs-progs: Fix up memory leakage

On 09/25/2012 12:14 PM, David Sterba wrote:
> On Tue, Sep 25, 2012 at 10:02:16AM +0800, zwu.kernel@...il.com wrote:
>> From: Zhi Yong Wu<wuzhy@...ux.vnet.ibm.com>
>>
>>    Some code pathes forget to free memory on exit.
>
> Same as with the fd's, kernel will free all memory for us at exit().

I strongly disagree with this approach. The callee often don't know what 
happen after and before the call. The same is true for the programmer, 
because the code is quite often updated by several people. A clean 
exit() is the right thing to do as general rule. I don't see any valid 
reason (in the btrfs context) to do otherwise.

Relying on the exit() for a proper clean-up increase the likelihood of 
bug when the code evolves (see my patch   [RESPOST][BTRFS-PROGS][PATCH] 
btrfs_read_dev_super(): uninitialized variable for an example of what 
means an incorrect deallocation of resource).

> If there's lots of memory allocated, it may be even faster to leave the
> unallocation process to kernel as it will do it in one go, while the
> application would unnecessarily free it chunk by chunk.

May be I am wrong, but I don't think that the increase of speed of the 
btrfs "command" is even measurable relying on exit instead of free()-ing 
each chunk of memory one at time.... The same should be true for the 
open()/close()

My 2¢

BR
G.Baroncelli

>
> david
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