linux-kernel - Re: kmemleak for MIPS

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Message-ID: <1301485085.29074.61.camel@e102109-lin.cambridge.arm.com>
Date:	Wed, 30 Mar 2011 12:38:05 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Daniel Baluta <dbaluta@...acom.com>
Cc:	Maxin John <maxin.john@...il.com>,
	naveen yadav <yad.naveen@...il.com>, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: kmemleak for MIPS

On Wed, 2011-03-30 at 12:24 +0100, Daniel Baluta wrote:
> We have:
> 
> > UDP hash table entries: 128 (order: 0, 4096 bytes)
> > CONFIG_BASE_SMALL=0
> 
> udp_table_init looks like:
> 
>         if (!CONFIG_BASE_SMALL)
>                 table->hash = alloc_large_system_hash(name, .. &table->mask);
>         /*
>          * Make sure hash table has the minimum size
>          */
> 
> Since CONFIG_BASE_SMALL is 0, we are allocating the hash using
> alloc_large_system
> Then:
>         if (CONFIG_BASE_SMALL || table->mask < UDP_HTABLE_SIZE_MIN - 1) {
>                 table->hash = kmalloc();
> 
> table->mask is 127, and UDP_HTABLE_SIZE_MIN is 256, so we are allocating again
> table->hash without freeing already allocated memory.

Indeed (on my ARM system the reported UDP hash table entries is 512, so
I don't get the memory leak).

> We could free table->hash, before allocating the memory with kmalloc.
> I don't fully understand the condition table->mask < UDP_HTABLE_SIZE_MIN - 1.

We don't have the equivalent of free_large_system_hash(). Reordering the
'if' blocks may be better.

-- 
Catalin


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